ICU for global collation

From 0b520194ed164feaeac94af25ddf1429cf4ab24f Mon Sep 17 00:00:00 2001
From: Peter Eisentraut <peter@eisentraut.org>
Date: Mon, 7 Oct 2019 12:21:36 +0200
Subject: [PATCH v1.2] Add option to use ICU as global collation provider

This adds the option to use ICU as the default collation provider for
either the whole cluster or a database.  New options for initdb,
createdb, and CREATE DATABASE are used to select this.
---
 doc/src/sgml/ref/createdb.sgml       |   9 ++
 doc/src/sgml/ref/initdb.sgml         |  23 ++++
 src/backend/access/hash/hashfunc.c   |  18 ++-
 src/backend/commands/dbcommands.c    |  52 ++++++++-
 src/backend/regex/regc_pg_locale.c   |   7 +-
 src/backend/utils/adt/formatting.c   |   6 +
 src/backend/utils/adt/like.c         |  20 +++-
 src/backend/utils/adt/like_support.c |   2 +
 src/backend/utils/adt/pg_locale.c    | 168 ++++++++++++++++-----------
 src/backend/utils/adt/varchar.c      |  22 +++-
 src/backend/utils/adt/varlena.c      |  26 ++++-
 src/backend/utils/init/postinit.c    |  21 ++++
 src/bin/initdb/Makefile              |   2 +
 src/bin/initdb/initdb.c              |  63 ++++++++--
 src/bin/initdb/t/001_initdb.pl       |  18 ++-
 src/bin/pg_dump/pg_dump.c            |  16 +++
 src/bin/psql/describe.c              |   8 ++
 src/bin/scripts/Makefile             |   2 +
 src/bin/scripts/createdb.c           |   9 ++
 src/bin/scripts/t/020_createdb.pl    |  19 ++-
 src/include/catalog/pg_database.dat  |   2 +-
 src/include/catalog/pg_database.h    |   3 +
 src/include/utils/pg_locale.h        |   6 +
 23 files changed, 417 insertions(+), 105 deletions(-)

diff --git a/doc/src/sgml/ref/createdb.sgml b/doc/src/sgml/ref/createdb.sgml
index 8fc8128bf9..5b73afad91 100644
--- a/doc/src/sgml/ref/createdb.sgml
+++ b/doc/src/sgml/ref/createdb.sgml
@@ -85,6 +85,15 @@ PostgreSQL documentation
       </listitem>
      </varlistentry>
 
+     <varlistentry>
+      <term><option>--collation-provider={<literal>libc</literal>|<literal>icu</literal>}</option></term>
+      <listitem>
+       <para>
+        Specifies the collation provider for the database.
+       </para>
+      </listitem>
+     </varlistentry>
+
      <varlistentry>
       <term><option>-D <replaceable class="parameter">tablespace</replaceable></option></term>
       <term><option>--tablespace=<replaceable class="parameter">tablespace</replaceable></option></term>
diff --git a/doc/src/sgml/ref/initdb.sgml b/doc/src/sgml/ref/initdb.sgml
index da5c8f5307..9ad7b2e112 100644
--- a/doc/src/sgml/ref/initdb.sgml
+++ b/doc/src/sgml/ref/initdb.sgml
@@ -165,6 +165,18 @@ PostgreSQL documentation
       </listitem>
      </varlistentry>
 
+     <varlistentry>
+      <term><option>--collation-provider={<literal>libc</literal>|<literal>icu</literal>}</option></term>
+      <listitem>
+       <para>
+        This option sets the collation provider for databases created in the
+        new cluster.  It can be overridden in the <command>CREATE
+        DATABASE</command> command when new databases are subsequently
+        created.  The default is <literal>libc</literal>.
+       </para>
+      </listitem>
+     </varlistentry>
+
      <varlistentry>
       <term><option>-D <replaceable class="parameter">directory</replaceable></option></term>
       <term><option>--pgdata=<replaceable class="parameter">directory</replaceable></option></term>
@@ -209,6 +221,17 @@ PostgreSQL documentation
       </listitem>
      </varlistentry>
 
+     <varlistentry>
+      <term><option>--icu-locale=<replaceable>locale</replaceable></option></term>
+      <listitem>
+       <para>
+        Specifies the ICU locale if the ICU collation provider is used.  If
+        this is not specified, the value from the <option>--locale</option>
+        option is used.
+       </para>
+      </listitem>
+     </varlistentry>
+
      <varlistentry id="app-initdb-data-checksums" xreflabel="data checksums">
       <term><option>-k</option></term>
       <term><option>--data-checksums</option></term>
diff --git a/src/backend/access/hash/hashfunc.c b/src/backend/access/hash/hashfunc.c
index 6ec1ec3df3..2f8f220549 100644
--- a/src/backend/access/hash/hashfunc.c
+++ b/src/backend/access/hash/hashfunc.c
@@ -255,8 +255,13 @@ hashtext(PG_FUNCTION_ARGS)
 				 errmsg("could not determine which collation to use for string hashing"),
 				 errhint("Use the COLLATE clause to set the collation explicitly.")));
 
-	if (!lc_collate_is_c(collid) && collid != DEFAULT_COLLATION_OID)
-		mylocale = pg_newlocale_from_collation(collid);
+	if (!lc_collate_is_c(collid))
+	{
+		if (collid != DEFAULT_COLLATION_OID)
+			mylocale = pg_newlocale_from_collation(collid);
+		else if (global_locale.provider == COLLPROVIDER_ICU)
+			mylocale = &global_locale;
+	}
 
 	if (!mylocale || mylocale->deterministic)
 	{
@@ -311,8 +316,13 @@ hashtextextended(PG_FUNCTION_ARGS)
 				 errmsg("could not determine which collation to use for string hashing"),
 				 errhint("Use the COLLATE clause to set the collation explicitly.")));
 
-	if (!lc_collate_is_c(collid) && collid != DEFAULT_COLLATION_OID)
-		mylocale = pg_newlocale_from_collation(collid);
+	if (!lc_collate_is_c(collid))
+	{
+		if (collid != DEFAULT_COLLATION_OID)
+			mylocale = pg_newlocale_from_collation(collid);
+		else if (global_locale.provider == COLLPROVIDER_ICU)
+			mylocale = &global_locale;
+	}
 
 	if (!mylocale || mylocale->deterministic)
 	{
diff --git a/src/backend/commands/dbcommands.c b/src/backend/commands/dbcommands.c
index 01d66212e9..e068c02d18 100644
--- a/src/backend/commands/dbcommands.c
+++ b/src/backend/commands/dbcommands.c
@@ -36,6 +36,7 @@
 #include "catalog/indexing.h"
 #include "catalog/objectaccess.h"
 #include "catalog/pg_authid.h"
+#include "catalog/pg_collation.h"
 #include "catalog/pg_database.h"
 #include "catalog/pg_db_role_setting.h"
 #include "catalog/pg_subscription.h"
@@ -87,7 +88,8 @@ static bool get_db_info(const char *name, LOCKMODE lockmode,
 						int *encodingP, bool *dbIsTemplateP, bool *dbAllowConnP,
 						Oid *dbLastSysOidP, TransactionId *dbFrozenXidP,
 						MultiXactId *dbMinMultiP,
-						Oid *dbTablespace, char **dbCollate, char **dbCtype);
+						Oid *dbTablespace, char **dbCollate, char **dbCtype,
+						char *dbCollProvider);
 static bool have_createdb_privilege(void);
 static void remove_dbtablespaces(Oid db_id);
 static bool check_db_file_conflict(Oid db_id);
@@ -107,6 +109,7 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 	int			src_encoding = -1;
 	char	   *src_collate = NULL;
 	char	   *src_ctype = NULL;
+	char		src_collprovider;
 	bool		src_istemplate;
 	bool		src_allowconn;
 	Oid			src_lastsysoid = InvalidOid;
@@ -128,6 +131,7 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 	DefElem    *dlocale = NULL;
 	DefElem    *dcollate = NULL;
 	DefElem    *dctype = NULL;
+	DefElem	   *dcollprovider = NULL;
 	DefElem    *distemplate = NULL;
 	DefElem    *dallowconnections = NULL;
 	DefElem    *dconnlimit = NULL;
@@ -136,6 +140,7 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 	const char *dbtemplate = NULL;
 	char	   *dbcollate = NULL;
 	char	   *dbctype = NULL;
+	char		dbcollprovider = '\0';
 	char	   *canonname;
 	int			encoding = -1;
 	bool		dbistemplate = false;
@@ -213,6 +218,15 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 						 parser_errposition(pstate, defel->location)));
 			dctype = defel;
 		}
+		else if (strcmp(defel->defname, "collation_provider") == 0)
+		{
+			if (dcollprovider)
+				ereport(ERROR,
+						(errcode(ERRCODE_SYNTAX_ERROR),
+						 errmsg("conflicting or redundant options"),
+						 parser_errposition(pstate, defel->location)));
+			dcollprovider = defel;
+		}
 		else if (strcmp(defel->defname, "is_template") == 0)
 		{
 			if (distemplate)
@@ -302,6 +316,23 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 		dbcollate = defGetString(dcollate);
 	if (dctype && dctype->arg)
 		dbctype = defGetString(dctype);
+	if (dcollprovider && dcollprovider->arg)
+	{
+		char	   *collproviderstr = defGetString(dcollprovider);
+
+#ifdef USE_ICU
+		if (pg_strcasecmp(collproviderstr, "icu") == 0)
+			dbcollprovider = COLLPROVIDER_ICU;
+		else
+#endif
+		if (pg_strcasecmp(collproviderstr, "libc") == 0)
+			dbcollprovider = COLLPROVIDER_LIBC;
+		else
+			ereport(ERROR,
+					(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
+					 errmsg("unrecognized collation provider: %s",
+							collproviderstr)));
+	}
 	if (distemplate && distemplate->arg)
 		dbistemplate = defGetBoolean(distemplate);
 	if (dallowconnections && dallowconnections->arg)
@@ -351,7 +382,7 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 					 &src_dboid, &src_owner, &src_encoding,
 					 &src_istemplate, &src_allowconn, &src_lastsysoid,
 					 &src_frozenxid, &src_minmxid, &src_deftablespace,
-					 &src_collate, &src_ctype))
+					 &src_collate, &src_ctype, &src_collprovider))
 		ereport(ERROR,
 				(errcode(ERRCODE_UNDEFINED_DATABASE),
 				 errmsg("template database \"%s\" does not exist",
@@ -377,6 +408,8 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 		dbcollate = src_collate;
 	if (dbctype == NULL)
 		dbctype = src_ctype;
+	if (dbcollprovider == '\0')
+		dbcollprovider = src_collprovider;
 
 	/* Some encodings are client only */
 	if (!PG_VALID_BE_ENCODING(encoding))
@@ -384,6 +417,8 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 				(errcode(ERRCODE_WRONG_OBJECT_TYPE),
 				 errmsg("invalid server encoding %d", encoding)));
 
+	if (dbcollprovider == COLLPROVIDER_LIBC)
+	{
 	/* Check that the chosen locales are valid, and get canonical spellings */
 	if (!check_locale(LC_COLLATE, dbcollate, &canonname))
 		ereport(ERROR,
@@ -397,6 +432,7 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 	dbctype = canonname;
 
 	check_encoding_locale_matches(encoding, dbcollate, dbctype);
+	}
 
 	/*
 	 * Check that the new encoding and locale settings match the source
@@ -560,6 +596,7 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 		DirectFunctionCall1(namein, CStringGetDatum(dbcollate));
 	new_record[Anum_pg_database_datctype - 1] =
 		DirectFunctionCall1(namein, CStringGetDatum(dbctype));
+	new_record[Anum_pg_database_datcollprovider - 1] = CharGetDatum(dbcollprovider);
 	new_record[Anum_pg_database_datistemplate - 1] = BoolGetDatum(dbistemplate);
 	new_record[Anum_pg_database_datallowconn - 1] = BoolGetDatum(dballowconnections);
 	new_record[Anum_pg_database_datconnlimit - 1] = Int32GetDatum(dbconnlimit);
@@ -833,7 +870,7 @@ dropdb(const char *dbname, bool missing_ok)
 	pgdbrel = table_open(DatabaseRelationId, RowExclusiveLock);
 
 	if (!get_db_info(dbname, AccessExclusiveLock, &db_id, NULL, NULL,
-					 &db_istemplate, NULL, NULL, NULL, NULL, NULL, NULL, NULL))
+					 &db_istemplate, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL))
 	{
 		if (!missing_ok)
 		{
@@ -1024,7 +1061,7 @@ RenameDatabase(const char *oldname, const char *newname)
 	rel = table_open(DatabaseRelationId, RowExclusiveLock);
 
 	if (!get_db_info(oldname, AccessExclusiveLock, &db_id, NULL, NULL,
-					 NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL))
+					 NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL))
 		ereport(ERROR,
 				(errcode(ERRCODE_UNDEFINED_DATABASE),
 				 errmsg("database \"%s\" does not exist", oldname)));
@@ -1137,7 +1174,7 @@ movedb(const char *dbname, const char *tblspcname)
 	pgdbrel = table_open(DatabaseRelationId, RowExclusiveLock);
 
 	if (!get_db_info(dbname, AccessExclusiveLock, &db_id, NULL, NULL,
-					 NULL, NULL, NULL, NULL, NULL, &src_tblspcoid, NULL, NULL))
+					 NULL, NULL, NULL, NULL, NULL, &src_tblspcoid, NULL, NULL, NULL))
 		ereport(ERROR,
 				(errcode(ERRCODE_UNDEFINED_DATABASE),
 				 errmsg("database \"%s\" does not exist", dbname)));
@@ -1769,7 +1806,8 @@ get_db_info(const char *name, LOCKMODE lockmode,
 			int *encodingP, bool *dbIsTemplateP, bool *dbAllowConnP,
 			Oid *dbLastSysOidP, TransactionId *dbFrozenXidP,
 			MultiXactId *dbMinMultiP,
-			Oid *dbTablespace, char **dbCollate, char **dbCtype)
+			Oid *dbTablespace, char **dbCollate, char **dbCtype,
+			char *dbCollProvider)
 {
 	bool		result = false;
 	Relation	relation;
@@ -1866,6 +1904,8 @@ get_db_info(const char *name, LOCKMODE lockmode,
 					*dbCollate = pstrdup(NameStr(dbform->datcollate));
 				if (dbCtype)
 					*dbCtype = pstrdup(NameStr(dbform->datctype));
+				if (dbCollProvider)
+					*dbCollProvider = dbform->datcollprovider;
 				ReleaseSysCache(tuple);
 				result = true;
 				break;
diff --git a/src/backend/regex/regc_pg_locale.c b/src/backend/regex/regc_pg_locale.c
index 4a808b7606..510bd71371 100644
--- a/src/backend/regex/regc_pg_locale.c
+++ b/src/backend/regex/regc_pg_locale.c
@@ -241,7 +241,12 @@ pg_set_regex_collation(Oid collation)
 	else
 	{
 		if (collation == DEFAULT_COLLATION_OID)
-			pg_regex_locale = 0;
+		{
+			if (global_locale.provider == COLLPROVIDER_ICU)
+				pg_regex_locale = &global_locale;
+			else
+				pg_regex_locale = 0;
+		}
 		else if (OidIsValid(collation))
 		{
 			/*
diff --git a/src/backend/utils/adt/formatting.c b/src/backend/utils/adt/formatting.c
index f7175df8da..dca8ca566f 100644
--- a/src/backend/utils/adt/formatting.c
+++ b/src/backend/utils/adt/formatting.c
@@ -1674,6 +1674,8 @@ str_tolower(const char *buff, size_t nbytes, Oid collid)
 			}
 			mylocale = pg_newlocale_from_collation(collid);
 		}
+		else if (global_locale.provider == COLLPROVIDER_ICU)
+			mylocale = &global_locale;
 
 #ifdef USE_ICU
 		if (mylocale && mylocale->provider == COLLPROVIDER_ICU)
@@ -1798,6 +1800,8 @@ str_toupper(const char *buff, size_t nbytes, Oid collid)
 			}
 			mylocale = pg_newlocale_from_collation(collid);
 		}
+		else if (global_locale.provider == COLLPROVIDER_ICU)
+			mylocale = &global_locale;
 
 #ifdef USE_ICU
 		if (mylocale && mylocale->provider == COLLPROVIDER_ICU)
@@ -1923,6 +1927,8 @@ str_initcap(const char *buff, size_t nbytes, Oid collid)
 			}
 			mylocale = pg_newlocale_from_collation(collid);
 		}
+		else if (global_locale.provider == COLLPROVIDER_ICU)
+			mylocale = &global_locale;
 
 #ifdef USE_ICU
 		if (mylocale && mylocale->provider == COLLPROVIDER_ICU)
diff --git a/src/backend/utils/adt/like.c b/src/backend/utils/adt/like.c
index 13d5cb083c..57dd3fe59d 100644
--- a/src/backend/utils/adt/like.c
+++ b/src/backend/utils/adt/like.c
@@ -150,9 +150,14 @@ SB_lower_char(unsigned char c, pg_locale_t locale, bool locale_is_c)
 static inline int
 GenericMatchText(const char *s, int slen, const char *p, int plen, Oid collation)
 {
-	if (collation && !lc_ctype_is_c(collation) && collation != DEFAULT_COLLATION_OID)
+	if (collation && !lc_ctype_is_c(collation))
 	{
-		pg_locale_t locale = pg_newlocale_from_collation(collation);
+		pg_locale_t locale = 0;
+
+		if (collation != DEFAULT_COLLATION_OID)
+			locale = pg_newlocale_from_collation(collation);
+		else if (global_locale.provider == COLLPROVIDER_ICU)
+			locale = &global_locale;
 
 		if (locale && !locale->deterministic)
 			ereport(ERROR,
@@ -195,11 +200,14 @@ Generic_Text_IC_like(text *str, text *pat, Oid collation)
 		}
 		locale = pg_newlocale_from_collation(collation);
 
-		if (locale && !locale->deterministic)
-			ereport(ERROR,
-					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-					 errmsg("nondeterministic collations are not supported for ILIKE")));
 	}
+	else if (global_locale.provider == COLLPROVIDER_ICU)
+		locale = &global_locale;
+
+	if (locale && !locale->deterministic)
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				 errmsg("nondeterministic collations are not supported for ILIKE")));
 
 	/*
 	 * For efficiency reasons, in the single byte case we don't call lower()
diff --git a/src/backend/utils/adt/like_support.c b/src/backend/utils/adt/like_support.c
index c8fec7863f..09a28aab8e 100644
--- a/src/backend/utils/adt/like_support.c
+++ b/src/backend/utils/adt/like_support.c
@@ -966,6 +966,8 @@ like_fixed_prefix(Const *patt_const, bool case_insensitive, Oid collation,
 			}
 			locale = pg_newlocale_from_collation(collation);
 		}
+		else if (global_locale.provider == COLLPROVIDER_ICU)
+			locale = &global_locale;
 	}
 
 	if (typeid != BYTEAOID)
diff --git a/src/backend/utils/adt/pg_locale.c b/src/backend/utils/adt/pg_locale.c
index b2f08ead45..168890b6f6 100644
--- a/src/backend/utils/adt/pg_locale.c
+++ b/src/backend/utils/adt/pg_locale.c
@@ -1206,6 +1206,9 @@ lc_collate_is_c(Oid collation)
 		static int	result = -1;
 		char	   *localeptr;
 
+		if (global_locale.provider == COLLPROVIDER_ICU)
+			return false;
+
 		if (result >= 0)
 			return (bool) result;
 		localeptr = setlocale(LC_COLLATE, NULL);
@@ -1256,6 +1259,9 @@ lc_ctype_is_c(Oid collation)
 		static int	result = -1;
 		char	   *localeptr;
 
+		if (global_locale.provider == COLLPROVIDER_ICU)
+			return false;
+
 		if (result >= 0)
 			return (bool) result;
 		localeptr = setlocale(LC_CTYPE, NULL);
@@ -1284,6 +1290,89 @@ lc_ctype_is_c(Oid collation)
 	return (lookup_collation_cache(collation, true))->ctype_is_c;
 }
 
+struct pg_locale_struct global_locale;
+
+void
+make_icu_collator(const char *collcollate, const char *collctype,
+				  struct pg_locale_struct *resultp)
+{
+#ifdef USE_ICU
+	UCollator  *collator;
+	UErrorCode	status;
+
+	if (strcmp(collcollate, collctype) != 0)
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				 errmsg("collations with different collate and ctype values are not supported by ICU")));
+
+	status = U_ZERO_ERROR;
+	collator = ucol_open(collcollate, &status);
+	if (U_FAILURE(status))
+		ereport(ERROR,
+				(errmsg("could not open collator for locale \"%s\": %s",
+						collcollate, u_errorName(status))));
+
+	if (U_ICU_VERSION_MAJOR_NUM < 54)
+		icu_set_collation_attributes(collator, collcollate);
+
+	/* We will leak this string if we get an error below :-( */
+	resultp->info.icu.locale = MemoryContextStrdup(TopMemoryContext,
+														   collcollate);
+	resultp->info.icu.ucol = collator;
+#else							/* not USE_ICU */
+	/* could get here if a collation was created by a build with ICU */
+	ereport(ERROR,
+			(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+			 errmsg("ICU is not supported in this build"), \
+			 errhint("You need to rebuild PostgreSQL using --with-icu.")));
+#endif							/* not USE_ICU */
+}
+
+void
+check_collation_version(HeapTuple colltuple)
+{
+	Form_pg_collation collform;
+	Datum		collversion;
+	bool		isnull;
+
+	collform = (Form_pg_collation) GETSTRUCT(colltuple);
+
+	collversion = SysCacheGetAttr(COLLOID, colltuple, Anum_pg_collation_collversion,
+								  &isnull);
+	if (!isnull)
+	{
+		char	   *actual_versionstr;
+		char	   *collversionstr;
+
+		actual_versionstr = get_collation_actual_version(collform->collprovider,
+														 NameStr(collform->collcollate));
+		if (!actual_versionstr)
+		{
+			/*
+			 * This could happen when specifying a version in CREATE
+			 * COLLATION for a libc locale, or manually creating a mess in
+			 * the catalogs.
+			 */
+			ereport(ERROR,
+					(errmsg("collation \"%s\" has no actual version, but a version was specified",
+							NameStr(collform->collname))));
+		}
+		collversionstr = TextDatumGetCString(collversion);
+
+		if (strcmp(actual_versionstr, collversionstr) != 0)
+			ereport(WARNING,
+					(errmsg("collation \"%s\" has version mismatch",
+							NameStr(collform->collname)),
+					 errdetail("The collation in the database was created using version %s, "
+							   "but the operating system provides version %s.",
+							   collversionstr, actual_versionstr),
+					 errhint("Rebuild all objects affected by this collation and run "
+							 "ALTER COLLATION %s REFRESH VERSION, "
+							 "or build PostgreSQL with the right library version.",
+							 quote_qualified_identifier(get_namespace_name(collform->collnamespace),
+														NameStr(collform->collname)))));
+	}
+}
 
 /* simple subroutine for reporting errors from newlocale() */
 #ifdef HAVE_LOCALE_T
@@ -1357,8 +1446,6 @@ pg_newlocale_from_collation(Oid collid)
 		const char *collctype pg_attribute_unused();
 		struct pg_locale_struct result;
 		pg_locale_t resultp;
-		Datum		collversion;
-		bool		isnull;
 
 		tp = SearchSysCache1(COLLOID, ObjectIdGetDatum(collid));
 		if (!HeapTupleIsValid(tp))
@@ -1428,72 +1515,10 @@ pg_newlocale_from_collation(Oid collid)
 		}
 		else if (collform->collprovider == COLLPROVIDER_ICU)
 		{
-#ifdef USE_ICU
-			UCollator  *collator;
-			UErrorCode	status;
-
-			if (strcmp(collcollate, collctype) != 0)
-				ereport(ERROR,
-						(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-						 errmsg("collations with different collate and ctype values are not supported by ICU")));
-
-			status = U_ZERO_ERROR;
-			collator = ucol_open(collcollate, &status);
-			if (U_FAILURE(status))
-				ereport(ERROR,
-						(errmsg("could not open collator for locale \"%s\": %s",
-								collcollate, u_errorName(status))));
-
-			if (U_ICU_VERSION_MAJOR_NUM < 54)
-				icu_set_collation_attributes(collator, collcollate);
-
-			/* We will leak this string if we get an error below :-( */
-			result.info.icu.locale = MemoryContextStrdup(TopMemoryContext,
-														 collcollate);
-			result.info.icu.ucol = collator;
-#else							/* not USE_ICU */
-			/* could get here if a collation was created by a build with ICU */
-			ereport(ERROR,
-					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-					 errmsg("ICU is not supported in this build"), \
-					 errhint("You need to rebuild PostgreSQL using --with-icu.")));
-#endif							/* not USE_ICU */
+			make_icu_collator(collcollate, collctype, &result);
 		}
 
-		collversion = SysCacheGetAttr(COLLOID, tp, Anum_pg_collation_collversion,
-									  &isnull);
-		if (!isnull)
-		{
-			char	   *actual_versionstr;
-			char	   *collversionstr;
-
-			actual_versionstr = get_collation_actual_version(collform->collprovider, collcollate);
-			if (!actual_versionstr)
-			{
-				/*
-				 * This could happen when specifying a version in CREATE
-				 * COLLATION for a libc locale, or manually creating a mess in
-				 * the catalogs.
-				 */
-				ereport(ERROR,
-						(errmsg("collation \"%s\" has no actual version, but a version was specified",
-								NameStr(collform->collname))));
-			}
-			collversionstr = TextDatumGetCString(collversion);
-
-			if (strcmp(actual_versionstr, collversionstr) != 0)
-				ereport(WARNING,
-						(errmsg("collation \"%s\" has version mismatch",
-								NameStr(collform->collname)),
-						 errdetail("The collation in the database was created using version %s, "
-								   "but the operating system provides version %s.",
-								   collversionstr, actual_versionstr),
-						 errhint("Rebuild all objects affected by this collation and run "
-								 "ALTER COLLATION %s REFRESH VERSION, "
-								 "or build PostgreSQL with the right library version.",
-								 quote_qualified_identifier(get_namespace_name(collform->collnamespace),
-															NameStr(collform->collname)))));
-		}
+		check_collation_version(tp);
 
 		ReleaseSysCache(tp);
 
@@ -1520,6 +1545,17 @@ get_collation_actual_version(char collprovider, const char *collcollate)
 {
 	char	   *collversion;
 
+	if (collprovider == COLLPROVIDER_DEFAULT)
+	{
+#ifdef USE_ICU
+		if (global_locale.provider == COLLPROVIDER_ICU)
+			collversion = get_collation_actual_version(global_locale.provider,
+													   global_locale.info.icu.locale);
+		else
+#endif
+			collversion = NULL;
+	}
+	else
 #ifdef USE_ICU
 	if (collprovider == COLLPROVIDER_ICU)
 	{
diff --git a/src/backend/utils/adt/varchar.c b/src/backend/utils/adt/varchar.c
index e63a4e553b..d1b6ccc6a3 100644
--- a/src/backend/utils/adt/varchar.c
+++ b/src/backend/utils/adt/varchar.c
@@ -751,7 +751,7 @@ bpchareq(PG_FUNCTION_ARGS)
 	len2 = bcTruelen(arg2);
 
 	if (lc_collate_is_c(collid) ||
-		collid == DEFAULT_COLLATION_OID ||
+		(collid == DEFAULT_COLLATION_OID && global_locale.deterministic) ||
 		pg_newlocale_from_collation(collid)->deterministic)
 	{
 		/*
@@ -789,7 +789,7 @@ bpcharne(PG_FUNCTION_ARGS)
 	len2 = bcTruelen(arg2);
 
 	if (lc_collate_is_c(collid) ||
-		collid == DEFAULT_COLLATION_OID ||
+		(collid == DEFAULT_COLLATION_OID && global_locale.deterministic) ||
 		pg_newlocale_from_collation(collid)->deterministic)
 	{
 		/*
@@ -995,8 +995,13 @@ hashbpchar(PG_FUNCTION_ARGS)
 	keydata = VARDATA_ANY(key);
 	keylen = bcTruelen(key);
 
-	if (!lc_collate_is_c(collid) && collid != DEFAULT_COLLATION_OID)
-		mylocale = pg_newlocale_from_collation(collid);
+	if (!lc_collate_is_c(collid))
+	{
+		if (collid != DEFAULT_COLLATION_OID)
+			mylocale = pg_newlocale_from_collation(collid);
+		else if (global_locale.provider == COLLPROVIDER_ICU)
+			mylocale = &global_locale;
+	}
 
 	if (!mylocale || mylocale->deterministic)
 	{
@@ -1055,8 +1060,13 @@ hashbpcharextended(PG_FUNCTION_ARGS)
 	keydata = VARDATA_ANY(key);
 	keylen = bcTruelen(key);
 
-	if (!lc_collate_is_c(collid) && collid != DEFAULT_COLLATION_OID)
-		mylocale = pg_newlocale_from_collation(collid);
+	if (!lc_collate_is_c(collid))
+	{
+		if (collid != DEFAULT_COLLATION_OID)
+			mylocale = pg_newlocale_from_collation(collid);
+		else if (global_locale.provider == COLLPROVIDER_ICU)
+			mylocale = &global_locale;
+	}
 
 	if (!mylocale || mylocale->deterministic)
 	{
diff --git a/src/backend/utils/adt/varlena.c b/src/backend/utils/adt/varlena.c
index 722b2c722d..0543a0688c 100644
--- a/src/backend/utils/adt/varlena.c
+++ b/src/backend/utils/adt/varlena.c
@@ -1156,8 +1156,13 @@ text_position_setup(text *t1, text *t2, Oid collid, TextPositionState *state)
 
 	check_collation_set(collid);
 
-	if (!lc_collate_is_c(collid) && collid != DEFAULT_COLLATION_OID)
-		mylocale = pg_newlocale_from_collation(collid);
+	if (!lc_collate_is_c(collid))
+	{
+		if (collid != DEFAULT_COLLATION_OID)
+			mylocale = pg_newlocale_from_collation(collid);
+		else if (global_locale.provider == COLLPROVIDER_ICU)
+			mylocale = &global_locale;
+	}
 
 	if (mylocale && !mylocale->deterministic)
 		ereport(ERROR,
@@ -1499,6 +1504,8 @@ varstr_cmp(const char *arg1, int len1, const char *arg2, int len2, Oid collid)
 
 		if (collid != DEFAULT_COLLATION_OID)
 			mylocale = pg_newlocale_from_collation(collid);
+		else if (global_locale.provider == COLLPROVIDER_ICU)
+			mylocale = &global_locale;
 
 		/*
 		 * memcmp() can't tell us which of two unequal strings sorts first,
@@ -1720,7 +1727,7 @@ texteq(PG_FUNCTION_ARGS)
 	check_collation_set(collid);
 
 	if (lc_collate_is_c(collid) ||
-		collid == DEFAULT_COLLATION_OID ||
+		(collid == DEFAULT_COLLATION_OID && global_locale.deterministic) ||
 		pg_newlocale_from_collation(collid)->deterministic)
 	{
 		Datum		arg1 = PG_GETARG_DATUM(0);
@@ -1774,7 +1781,7 @@ textne(PG_FUNCTION_ARGS)
 	check_collation_set(collid);
 
 	if (lc_collate_is_c(collid) ||
-		collid == DEFAULT_COLLATION_OID ||
+		(collid == DEFAULT_COLLATION_OID && global_locale.deterministic) ||
 		pg_newlocale_from_collation(collid)->deterministic)
 	{
 		Datum		arg1 = PG_GETARG_DATUM(0);
@@ -1886,8 +1893,13 @@ text_starts_with(PG_FUNCTION_ARGS)
 
 	check_collation_set(collid);
 
-	if (!lc_collate_is_c(collid) && collid != DEFAULT_COLLATION_OID)
-		mylocale = pg_newlocale_from_collation(collid);
+	if (!lc_collate_is_c(collid))
+	{
+		if (collid != DEFAULT_COLLATION_OID)
+			mylocale = pg_newlocale_from_collation(collid);
+		else if (global_locale.provider == COLLPROVIDER_ICU)
+			mylocale = &global_locale;
+	}
 
 	if (mylocale && !mylocale->deterministic)
 		ereport(ERROR,
@@ -2002,6 +2014,8 @@ varstr_sortsupport(SortSupport ssup, Oid typid, Oid collid)
 		 */
 		if (collid != DEFAULT_COLLATION_OID)
 			locale = pg_newlocale_from_collation(collid);
+		else if (global_locale.provider == COLLPROVIDER_ICU)
+			locale = &global_locale;
 
 		/*
 		 * There is a further exception on Windows.  When the database
diff --git a/src/backend/utils/init/postinit.c b/src/backend/utils/init/postinit.c
index 29c5ec7b58..1a91b42798 100644
--- a/src/backend/utils/init/postinit.c
+++ b/src/backend/utils/init/postinit.c
@@ -31,6 +31,7 @@
 #include "catalog/indexing.h"
 #include "catalog/namespace.h"
 #include "catalog/pg_authid.h"
+#include "catalog/pg_collation.h"
 #include "catalog/pg_database.h"
 #include "catalog/pg_db_role_setting.h"
 #include "catalog/pg_tablespace.h"
@@ -404,6 +405,8 @@ CheckMyDatabase(const char *name, bool am_superuser, bool override_allow_connect
 	collate = NameStr(dbform->datcollate);
 	ctype = NameStr(dbform->datctype);
 
+	if (dbform->datcollprovider == COLLPROVIDER_LIBC)
+	{
 	if (pg_perm_setlocale(LC_COLLATE, collate) == NULL)
 		ereport(FATAL,
 				(errmsg("database locale is incompatible with operating system"),
@@ -417,6 +420,24 @@ CheckMyDatabase(const char *name, bool am_superuser, bool override_allow_connect
 				 errdetail("The database was initialized with LC_CTYPE \"%s\", "
 						   " which is not recognized by setlocale().", ctype),
 				 errhint("Recreate the database with another locale or install the missing locale.")));
+	}
+	else if (dbform->datcollprovider == COLLPROVIDER_ICU)
+	{
+		make_icu_collator(collate, ctype, &global_locale);
+	}
+
+	global_locale.provider = dbform->datcollprovider;
+	global_locale.deterministic = true;	// TODO
+
+	{
+		HeapTuple	tp;
+
+		tp = SearchSysCache1(COLLOID, ObjectIdGetDatum(DEFAULT_COLLATION_OID));
+		if (!HeapTupleIsValid(tp))
+			elog(ERROR, "cache lookup failed for collation %u", DEFAULT_COLLATION_OID);
+		check_collation_version(tp);
+		ReleaseSysCache(tp);
+	}
 
 	/* Make the locale settings visible as GUC variables, too */
 	SetConfigOption("lc_collate", collate, PGC_INTERNAL, PGC_S_OVERRIDE);
diff --git a/src/bin/initdb/Makefile b/src/bin/initdb/Makefile
index 7c404430a9..a9335a8ba6 100644
--- a/src/bin/initdb/Makefile
+++ b/src/bin/initdb/Makefile
@@ -61,6 +61,8 @@ clean distclean maintainer-clean:
 # ensure that changes in datadir propagate into object file
 initdb.o: initdb.c $(top_builddir)/src/Makefile.global
 
+export with_icu
+
 check:
 	$(prove_check)
 
diff --git a/src/bin/initdb/initdb.c b/src/bin/initdb/initdb.c
index 88a261d9bd..62c310040a 100644
--- a/src/bin/initdb/initdb.c
+++ b/src/bin/initdb/initdb.c
@@ -129,6 +129,8 @@ static char *lc_monetary = NULL;
 static char *lc_numeric = NULL;
 static char *lc_time = NULL;
 static char *lc_messages = NULL;
+static char collation_provider[] = {COLLPROVIDER_LIBC, '\0'};
+static char *icu_locale = NULL;
 static const char *default_text_search_config = NULL;
 static char *username = NULL;
 static bool pwprompt = false;
@@ -1412,10 +1414,13 @@ bootstrap_template1(void)
 							  encodingid_to_string(encodingid));
 
 	bki_lines = replace_token(bki_lines, "LC_COLLATE",
-							  escape_quotes_bki(lc_collate));
+							  escape_quotes_bki(collation_provider[0] == COLLPROVIDER_ICU ? icu_locale : lc_collate));
 
 	bki_lines = replace_token(bki_lines, "LC_CTYPE",
-							  escape_quotes_bki(lc_ctype));
+							  escape_quotes_bki(collation_provider[0] == COLLPROVIDER_ICU ? icu_locale : lc_ctype));
+
+	bki_lines = replace_token(bki_lines, "COLLPROVIDER",
+							  collation_provider);
 
 	/* Also ensure backend isn't confused by this environment var: */
 	unsetenv("PGCLIENTENCODING");
@@ -1707,6 +1712,12 @@ setup_description(FILE *cmdfd)
 static void
 setup_collation(FILE *cmdfd)
 {
+	/*
+	 * Set version of the default collation.
+	 */
+	PG_CMD_PRINTF("UPDATE pg_collation SET collversion = pg_collation_actual_version(oid) WHERE oid = %d;\n\n",
+				  DEFAULT_COLLATION_OID);
+
 	/*
 	 * Add an SQL-standard name.  We don't want to pin this, so it doesn't go
 	 * in pg_collation.h.  But add it before reading system collations, so
@@ -1995,8 +2006,6 @@ make_template0(FILE *cmdfd)
 {
 	const char *const *line;
 	static const char *const template0_setup[] = {
-		"CREATE DATABASE template0 IS_TEMPLATE = true ALLOW_CONNECTIONS = false;\n\n",
-
 		/*
 		 * We use the OID of template0 to determine datlastsysoid
 		 */
@@ -2021,6 +2030,9 @@ make_template0(FILE *cmdfd)
 		NULL
 	};
 
+	PG_CMD_PRINTF("CREATE DATABASE template0 IS_TEMPLATE = true ALLOW_CONNECTIONS = false COLLATION_PROVIDER = %s;\n\n",
+				  collation_provider[0] == COLLPROVIDER_ICU ? "icu" : "libc");
+
 	for (line = template0_setup; *line; line++)
 		PG_CMD_PUTS(*line);
 }
@@ -2293,13 +2305,14 @@ setlocales(void)
 			lc_monetary = locale;
 		if (!lc_messages)
 			lc_messages = locale;
+		if (!icu_locale)
+			icu_locale = locale;
 	}
 
 	/*
 	 * canonicalize locale names, and obtain any missing values from our
 	 * current environment
 	 */
-
 	check_locale_name(LC_CTYPE, lc_ctype, &canonname);
 	lc_ctype = canonname;
 	check_locale_name(LC_COLLATE, lc_collate, &canonname);
@@ -2318,6 +2331,18 @@ setlocales(void)
 	check_locale_name(LC_CTYPE, lc_messages, &canonname);
 	lc_messages = canonname;
 #endif
+
+	/*
+	 * If ICU is selected but no ICU locale has been given, take the
+	 * lc_collate locale and chop off any encoding suffix.  This should give
+	 * the user a configuration that resembles their operating system's locale
+	 * setup.
+	 */
+	if (collation_provider[0] == COLLPROVIDER_ICU && !icu_locale)
+	{
+		icu_locale = pg_strdup(lc_collate);
+		icu_locale[strcspn(icu_locale, ".")] = '\0';
+	}
 }
 
 /*
@@ -2333,9 +2358,12 @@ usage(const char *progname)
 	printf(_("  -A, --auth=METHOD         default authentication method for local connections\n"));
 	printf(_("      --auth-host=METHOD    default authentication method for local TCP/IP connections\n"));
 	printf(_("      --auth-local=METHOD   default authentication method for local-socket connections\n"));
+	printf(_("      --collation-provider={libc|icu}\n"
+			 "                            set default collation provider for new databases\n"));
 	printf(_(" [-D, --pgdata=]DATADIR     location for this database cluster\n"));
 	printf(_("  -E, --encoding=ENCODING   set default encoding for new databases\n"));
 	printf(_("  -g, --allow-group-access  allow group read/execute on data directory\n"));
+	printf(_("      --icu-locale          set ICU locale for new databases\n"));
 	printf(_("      --locale=LOCALE       set default locale for new databases\n"));
 	printf(_("      --lc-collate=, --lc-ctype=, --lc-messages=LOCALE\n"
 			 "      --lc-monetary=, --lc-numeric=, --lc-time=LOCALE\n"
@@ -2510,7 +2538,8 @@ setup_locale_encoding(void)
 		strcmp(lc_ctype, lc_time) == 0 &&
 		strcmp(lc_ctype, lc_numeric) == 0 &&
 		strcmp(lc_ctype, lc_monetary) == 0 &&
-		strcmp(lc_ctype, lc_messages) == 0)
+		strcmp(lc_ctype, lc_messages) == 0 &&
+		(!icu_locale || strcmp(lc_ctype, icu_locale) == 0))
 		printf(_("The database cluster will be initialized with locale \"%s\".\n"), lc_ctype);
 	else
 	{
@@ -2527,9 +2556,13 @@ setup_locale_encoding(void)
 			   lc_monetary,
 			   lc_numeric,
 			   lc_time);
+		if (icu_locale)
+			printf(_("  ICU:      %s\n"), icu_locale);
 	}
 
-	if (!encoding)
+	if (!encoding && collation_provider[0] == COLLPROVIDER_ICU)
+		encodingid = PG_UTF8;
+	else if (!encoding)
 	{
 		int			ctype_enc;
 
@@ -3029,6 +3062,8 @@ main(int argc, char *argv[])
 		{"wal-segsize", required_argument, NULL, 12},
 		{"data-checksums", no_argument, NULL, 'k'},
 		{"allow-group-access", no_argument, NULL, 'g'},
+		{"collation-provider", required_argument, NULL, 13},
+		{"icu-locale", required_argument, NULL, 14},
 		{NULL, 0, NULL, 0}
 	};
 
@@ -3167,6 +3202,20 @@ main(int argc, char *argv[])
 			case 'g':
 				SetDataDirectoryCreatePerm(PG_DIR_MODE_GROUP);
 				break;
+			case 13:
+				if (strcmp(optarg, "icu") == 0)
+					collation_provider[0] = COLLPROVIDER_ICU;
+				else if (strcmp(optarg, "libc") == 0)
+					collation_provider[0] = COLLPROVIDER_LIBC;
+				else
+				{
+					pg_log_error("unrecognized collation provider: %s", optarg);
+					exit(1);
+				}
+				break;
+			case 14:
+				icu_locale = pg_strdup(optarg);
+				break;
 			default:
 				/* getopt_long already emitted a complaint */
 				fprintf(stderr, _("Try \"%s --help\" for more information.\n"),
diff --git a/src/bin/initdb/t/001_initdb.pl b/src/bin/initdb/t/001_initdb.pl
index 8387b945d3..90f6fc8f14 100644
--- a/src/bin/initdb/t/001_initdb.pl
+++ b/src/bin/initdb/t/001_initdb.pl
@@ -8,7 +8,7 @@ use Fcntl ':mode';
 use File::stat qw{lstat};
 use PostgresNode;
 use TestLib;
-use Test::More tests => 22;
+use Test::More tests => 24;
 
 my $tempdir = TestLib::tempdir;
 my $xlogdir = "$tempdir/pgxlog";
@@ -89,3 +89,19 @@ SKIP:
 	ok(check_mode_recursive($datadir_group, 0750, 0640),
 		'check PGDATA permissions');
 }
+
+# Collation provider tests
+
+if ($ENV{with_icu} eq 'yes')
+{
+	command_ok(['initdb', '--no-sync', '--collation-provider=icu', "$tempdir/data2"],
+			   'collation provider ICU');
+}
+else
+{
+	command_fails(['initdb', '--no-sync', '--collation-provider=icu', "$tempdir/data2"],
+				  'collation provider ICU fails since no ICU support');
+}
+
+command_fails(['initdb', '--no-sync', '--collation-provider=xyz', "$tempdir/dataX"],
+			  'fails for invalid collation provider');
diff --git a/src/bin/pg_dump/pg_dump.c b/src/bin/pg_dump/pg_dump.c
index f01fea5b91..9d7842583b 100644
--- a/src/bin/pg_dump/pg_dump.c
+++ b/src/bin/pg_dump/pg_dump.c
@@ -2638,6 +2638,7 @@ dumpDatabase(Archive *fout)
 				i_datname,
 				i_dba,
 				i_encoding,
+				i_datcollprovider,
 				i_collate,
 				i_ctype,
 				i_frozenxid,
@@ -2652,6 +2653,7 @@ dumpDatabase(Archive *fout)
 	const char *datname,
 			   *dba,
 			   *encoding,
+			   *datcollprovider,
 			   *collate,
 			   *ctype,
 			   *datacl,
@@ -2680,6 +2682,7 @@ dumpDatabase(Archive *fout)
 		appendPQExpBuffer(dbQry, "SELECT tableoid, oid, datname, "
 						  "(%s datdba) AS dba, "
 						  "pg_encoding_to_char(encoding) AS encoding, "
+						  "datcollprovider, "
 						  "datcollate, datctype, datfrozenxid, datminmxid, "
 						  "(SELECT array_agg(acl ORDER BY row_n) FROM "
 						  "  (SELECT acl, row_n FROM "
@@ -2772,6 +2775,7 @@ dumpDatabase(Archive *fout)
 	i_datname = PQfnumber(res, "datname");
 	i_dba = PQfnumber(res, "dba");
 	i_encoding = PQfnumber(res, "encoding");
+	i_datcollprovider = PQfnumber(res, "datcollprovider");
 	i_collate = PQfnumber(res, "datcollate");
 	i_ctype = PQfnumber(res, "datctype");
 	i_frozenxid = PQfnumber(res, "datfrozenxid");
@@ -2787,6 +2791,7 @@ dumpDatabase(Archive *fout)
 	datname = PQgetvalue(res, 0, i_datname);
 	dba = PQgetvalue(res, 0, i_dba);
 	encoding = PQgetvalue(res, 0, i_encoding);
+	datcollprovider = PQgetvalue(res, 0, i_datcollprovider);
 	collate = PQgetvalue(res, 0, i_collate);
 	ctype = PQgetvalue(res, 0, i_ctype);
 	frozenxid = atooid(PQgetvalue(res, 0, i_frozenxid));
@@ -2812,6 +2817,17 @@ dumpDatabase(Archive *fout)
 		appendPQExpBufferStr(creaQry, " ENCODING = ");
 		appendStringLiteralAH(creaQry, encoding, fout);
 	}
+	if (strlen(datcollprovider) > 0)
+	{
+		appendPQExpBufferStr(creaQry, " COLLATION_PROVIDER = ");
+		if (datcollprovider[0] == 'c')
+			appendPQExpBufferStr(creaQry, "libc");
+		else if (datcollprovider[0] == 'i')
+			appendPQExpBufferStr(creaQry, "icu");
+		else
+			fatal("unrecognized collation provider: %s",
+				  datcollprovider);
+	}
 	if (strlen(collate) > 0 && strcmp(collate, ctype) == 0)
 	{
 		appendPQExpBufferStr(creaQry, " LOCALE = ");
diff --git a/src/bin/psql/describe.c b/src/bin/psql/describe.c
index d7c0fc0c1e..23fdbb92ae 100644
--- a/src/bin/psql/describe.c
+++ b/src/bin/psql/describe.c
@@ -880,6 +880,14 @@ listAllDbs(const char *pattern, bool verbose)
 						  "       d.datctype as \"%s\",\n",
 						  gettext_noop("Collate"),
 						  gettext_noop("Ctype"));
+	if (pset.sversion >= 130000)
+		appendPQExpBuffer(&buf,
+						  "       CASE d.datcollprovider WHEN 'c' THEN 'libc' WHEN 'i' THEN 'icu' END AS \"%s\",\n",
+						  gettext_noop("Provider"));
+	else
+		appendPQExpBuffer(&buf,
+						  "       'libc' AS \"%s\",\n",
+						  gettext_noop("Provider"));
 	appendPQExpBufferStr(&buf, "       ");
 	printACLColumn(&buf, "d.datacl");
 	if (verbose && pset.sversion >= 80200)
diff --git a/src/bin/scripts/Makefile b/src/bin/scripts/Makefile
index ede665090f..ef4f8593dc 100644
--- a/src/bin/scripts/Makefile
+++ b/src/bin/scripts/Makefile
@@ -53,6 +53,8 @@ clean distclean maintainer-clean:
 	rm -f common.o scripts_parallel.o $(WIN32RES)
 	rm -rf tmp_check
 
+export with_icu
+
 check:
 	$(prove_check)
 
diff --git a/src/bin/scripts/createdb.c b/src/bin/scripts/createdb.c
index 64bcc20cb4..5944fd3f63 100644
--- a/src/bin/scripts/createdb.c
+++ b/src/bin/scripts/createdb.c
@@ -37,6 +37,7 @@ main(int argc, char *argv[])
 		{"lc-ctype", required_argument, NULL, 2},
 		{"locale", required_argument, NULL, 'l'},
 		{"maintenance-db", required_argument, NULL, 3},
+		{"collation-provider", required_argument, NULL, 4},
 		{NULL, 0, NULL, 0}
 	};
 
@@ -59,6 +60,7 @@ main(int argc, char *argv[])
 	char	   *lc_collate = NULL;
 	char	   *lc_ctype = NULL;
 	char	   *locale = NULL;
+	char	   *collation_provider = NULL;
 
 	PQExpBufferData sql;
 
@@ -117,6 +119,9 @@ main(int argc, char *argv[])
 			case 3:
 				maintenance_db = pg_strdup(optarg);
 				break;
+			case 4:
+				collation_provider = pg_strdup(optarg);
+				break;
 			default:
 				fprintf(stderr, _("Try \"%s --help\" for more information.\n"), progname);
 				exit(1);
@@ -193,6 +198,8 @@ main(int argc, char *argv[])
 		appendPQExpBuffer(&sql, " LC_COLLATE '%s'", lc_collate);
 	if (lc_ctype)
 		appendPQExpBuffer(&sql, " LC_CTYPE '%s'", lc_ctype);
+	if (collation_provider)
+		appendPQExpBuffer(&sql, " COLLATION_PROVIDER %s", collation_provider);
 
 	appendPQExpBufferChar(&sql, ';');
 
@@ -250,6 +257,8 @@ help(const char *progname)
 	printf(_("Usage:\n"));
 	printf(_("  %s [OPTION]... [DBNAME] [DESCRIPTION]\n"), progname);
 	printf(_("\nOptions:\n"));
+	printf(_("      --collation-provider={libc|icu}\n"
+			 "                               collation provider for the database\n"));
 	printf(_("  -D, --tablespace=TABLESPACE  default tablespace for the database\n"));
 	printf(_("  -e, --echo                   show the commands being sent to the server\n"));
 	printf(_("  -E, --encoding=ENCODING      encoding for the database\n"));
diff --git a/src/bin/scripts/t/020_createdb.pl b/src/bin/scripts/t/020_createdb.pl
index c0f6067a92..9e8220335f 100644
--- a/src/bin/scripts/t/020_createdb.pl
+++ b/src/bin/scripts/t/020_createdb.pl
@@ -3,7 +3,7 @@ use warnings;
 
 use PostgresNode;
 use TestLib;
-use Test::More tests => 13;
+use Test::More tests => 16;
 
 program_help_ok('createdb');
 program_version_ok('createdb');
@@ -22,5 +22,22 @@ $node->issues_sql_like(
 	qr/statement: CREATE DATABASE foobar2 ENCODING 'LATIN1'/,
 	'create database with encoding');
 
+if ($ENV{with_icu} eq 'yes')
+{
+	$node->issues_sql_like(
+		[ 'createdb', '-T', 'template0', '--collation-provider=icu', 'foobar3' ],
+		qr/statement: CREATE DATABASE foobar3 .* COLLATION_PROVIDER icu/,
+		'create database with ICU');
+}
+else
+{
+	$node->command_fails(
+		[ 'createdb', '-T', 'template0', '--collation-provider=icu', 'foobar3' ],
+		'create database with ICU fails since no ICU support');
+	pass;
+}
+
 $node->command_fails([ 'createdb', 'foobar1' ],
 	'fails if database already exists');
+$node->command_fails([ 'createdb', '-T', 'template0', '--collation-provider=xyz', 'foobarX' ],
+	'fails for invalid collation provider');
diff --git a/src/include/catalog/pg_database.dat b/src/include/catalog/pg_database.dat
index 89bd75d024..f261cdd838 100644
--- a/src/include/catalog/pg_database.dat
+++ b/src/include/catalog/pg_database.dat
@@ -15,7 +15,7 @@
 { oid => '1', oid_symbol => 'TemplateDbOid',
   descr => 'default template for new databases',
   datname => 'template1', encoding => 'ENCODING', datcollate => 'LC_COLLATE',
-  datctype => 'LC_CTYPE', datistemplate => 't', datallowconn => 't',
+  datctype => 'LC_CTYPE', datcollprovider => 'COLLPROVIDER', datistemplate => 't', datallowconn => 't',
   datconnlimit => '-1', datlastsysoid => '0', datfrozenxid => '0',
   datminmxid => '1', dattablespace => 'pg_default', datacl => '_null_' },
 
diff --git a/src/include/catalog/pg_database.h b/src/include/catalog/pg_database.h
index 06fea45f53..ab3c0951df 100644
--- a/src/include/catalog/pg_database.h
+++ b/src/include/catalog/pg_database.h
@@ -46,6 +46,9 @@ CATALOG(pg_database,1262,DatabaseRelationId) BKI_SHARED_RELATION BKI_ROWTYPE_OID
 	/* LC_CTYPE setting */
 	NameData	datctype;
 
+	/* see pg_collation.collprovider */
+	char		datcollprovider;
+
 	/* allowed as CREATE DATABASE template? */
 	bool		datistemplate;
 
diff --git a/src/include/utils/pg_locale.h b/src/include/utils/pg_locale.h
index b4b3aa5843..17fcee1e89 100644
--- a/src/include/utils/pg_locale.h
+++ b/src/include/utils/pg_locale.h
@@ -101,6 +101,12 @@ struct pg_locale_struct
 
 typedef struct pg_locale_struct *pg_locale_t;
 
+extern struct pg_locale_struct global_locale;
+
+extern void make_icu_collator(const char *collcollate, const char *collctype,
+							  struct pg_locale_struct *resultp);
+extern void check_collation_version(HeapTuple colltuple);
+
 extern pg_locale_t pg_newlocale_from_collation(Oid collid);
 
 extern char *get_collation_actual_version(char collprovider, const char *collcollate);
-- 
2.20.1

From 90fad2d7524620dca35d667aa3266cdb8fb16cac Mon Sep 17 00:00:00 2001
From: Peter Eisentraut <peter@eisentraut.org>
Date: Mon, 7 Oct 2019 12:21:36 +0200
Subject: [PATCH v2] Add option to use ICU as global collation provider

This adds the option to use ICU as the default collation provider for
either the whole cluster or a database.  New options for initdb,
createdb, and CREATE DATABASE are used to select this.
---
 doc/src/sgml/ref/createdb.sgml       |   9 ++
 doc/src/sgml/ref/initdb.sgml         |  23 ++++
 src/backend/access/hash/hashfunc.c   |  18 ++-
 src/backend/commands/dbcommands.c    |  52 ++++++++-
 src/backend/regex/regc_pg_locale.c   |   7 +-
 src/backend/utils/adt/formatting.c   |   6 +
 src/backend/utils/adt/like.c         |  20 +++-
 src/backend/utils/adt/like_support.c |   2 +
 src/backend/utils/adt/pg_locale.c    | 164 ++++++++++++++++-----------
 src/backend/utils/adt/varchar.c      |  22 +++-
 src/backend/utils/adt/varlena.c      |  26 ++++-
 src/backend/utils/init/postinit.c    |  21 ++++
 src/bin/initdb/Makefile              |   2 +
 src/bin/initdb/initdb.c              |  63 ++++++++--
 src/bin/initdb/t/001_initdb.pl       |  18 ++-
 src/bin/pg_dump/pg_dump.c            |  16 +++
 src/bin/psql/describe.c              |   8 ++
 src/bin/scripts/Makefile             |   2 +
 src/bin/scripts/createdb.c           |   9 ++
 src/bin/scripts/t/020_createdb.pl    |  19 +++-
 src/include/catalog/pg_database.dat  |   2 +-
 src/include/catalog/pg_database.h    |   3 +
 src/include/utils/pg_locale.h        |   6 +
 23 files changed, 413 insertions(+), 105 deletions(-)

diff --git a/doc/src/sgml/ref/createdb.sgml b/doc/src/sgml/ref/createdb.sgml
index 8fc8128bf9..5b73afad91 100644
--- a/doc/src/sgml/ref/createdb.sgml
+++ b/doc/src/sgml/ref/createdb.sgml
@@ -85,6 +85,15 @@ PostgreSQL documentation
       </listitem>
      </varlistentry>
 
+     <varlistentry>
+      <term><option>--collation-provider={<literal>libc</literal>|<literal>icu</literal>}</option></term>
+      <listitem>
+       <para>
+        Specifies the collation provider for the database.
+       </para>
+      </listitem>
+     </varlistentry>
+
      <varlistentry>
       <term><option>-D <replaceable class="parameter">tablespace</replaceable></option></term>
       <term><option>--tablespace=<replaceable class="parameter">tablespace</replaceable></option></term>
diff --git a/doc/src/sgml/ref/initdb.sgml b/doc/src/sgml/ref/initdb.sgml
index da5c8f5307..9ad7b2e112 100644
--- a/doc/src/sgml/ref/initdb.sgml
+++ b/doc/src/sgml/ref/initdb.sgml
@@ -165,6 +165,18 @@ PostgreSQL documentation
       </listitem>
      </varlistentry>
 
+     <varlistentry>
+      <term><option>--collation-provider={<literal>libc</literal>|<literal>icu</literal>}</option></term>
+      <listitem>
+       <para>
+        This option sets the collation provider for databases created in the
+        new cluster.  It can be overridden in the <command>CREATE
+        DATABASE</command> command when new databases are subsequently
+        created.  The default is <literal>libc</literal>.
+       </para>
+      </listitem>
+     </varlistentry>
+
      <varlistentry>
       <term><option>-D <replaceable class="parameter">directory</replaceable></option></term>
       <term><option>--pgdata=<replaceable class="parameter">directory</replaceable></option></term>
@@ -209,6 +221,17 @@ PostgreSQL documentation
       </listitem>
      </varlistentry>
 
+     <varlistentry>
+      <term><option>--icu-locale=<replaceable>locale</replaceable></option></term>
+      <listitem>
+       <para>
+        Specifies the ICU locale if the ICU collation provider is used.  If
+        this is not specified, the value from the <option>--locale</option>
+        option is used.
+       </para>
+      </listitem>
+     </varlistentry>
+
      <varlistentry id="app-initdb-data-checksums" xreflabel="data checksums">
       <term><option>-k</option></term>
       <term><option>--data-checksums</option></term>
diff --git a/src/backend/access/hash/hashfunc.c b/src/backend/access/hash/hashfunc.c
index 6ec1ec3df3..2f8f220549 100644
--- a/src/backend/access/hash/hashfunc.c
+++ b/src/backend/access/hash/hashfunc.c
@@ -255,8 +255,13 @@ hashtext(PG_FUNCTION_ARGS)
 				 errmsg("could not determine which collation to use for string hashing"),
 				 errhint("Use the COLLATE clause to set the collation explicitly.")));
 
-	if (!lc_collate_is_c(collid) && collid != DEFAULT_COLLATION_OID)
-		mylocale = pg_newlocale_from_collation(collid);
+	if (!lc_collate_is_c(collid))
+	{
+		if (collid != DEFAULT_COLLATION_OID)
+			mylocale = pg_newlocale_from_collation(collid);
+		else if (global_locale.provider == COLLPROVIDER_ICU)
+			mylocale = &global_locale;
+	}
 
 	if (!mylocale || mylocale->deterministic)
 	{
@@ -311,8 +316,13 @@ hashtextextended(PG_FUNCTION_ARGS)
 				 errmsg("could not determine which collation to use for string hashing"),
 				 errhint("Use the COLLATE clause to set the collation explicitly.")));
 
-	if (!lc_collate_is_c(collid) && collid != DEFAULT_COLLATION_OID)
-		mylocale = pg_newlocale_from_collation(collid);
+	if (!lc_collate_is_c(collid))
+	{
+		if (collid != DEFAULT_COLLATION_OID)
+			mylocale = pg_newlocale_from_collation(collid);
+		else if (global_locale.provider == COLLPROVIDER_ICU)
+			mylocale = &global_locale;
+	}
 
 	if (!mylocale || mylocale->deterministic)
 	{
diff --git a/src/backend/commands/dbcommands.c b/src/backend/commands/dbcommands.c
index 01d66212e9..e068c02d18 100644
--- a/src/backend/commands/dbcommands.c
+++ b/src/backend/commands/dbcommands.c
@@ -36,6 +36,7 @@
 #include "catalog/indexing.h"
 #include "catalog/objectaccess.h"
 #include "catalog/pg_authid.h"
+#include "catalog/pg_collation.h"
 #include "catalog/pg_database.h"
 #include "catalog/pg_db_role_setting.h"
 #include "catalog/pg_subscription.h"
@@ -87,7 +88,8 @@ static bool get_db_info(const char *name, LOCKMODE lockmode,
 						int *encodingP, bool *dbIsTemplateP, bool *dbAllowConnP,
 						Oid *dbLastSysOidP, TransactionId *dbFrozenXidP,
 						MultiXactId *dbMinMultiP,
-						Oid *dbTablespace, char **dbCollate, char **dbCtype);
+						Oid *dbTablespace, char **dbCollate, char **dbCtype,
+						char *dbCollProvider);
 static bool have_createdb_privilege(void);
 static void remove_dbtablespaces(Oid db_id);
 static bool check_db_file_conflict(Oid db_id);
@@ -107,6 +109,7 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 	int			src_encoding = -1;
 	char	   *src_collate = NULL;
 	char	   *src_ctype = NULL;
+	char		src_collprovider;
 	bool		src_istemplate;
 	bool		src_allowconn;
 	Oid			src_lastsysoid = InvalidOid;
@@ -128,6 +131,7 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 	DefElem    *dlocale = NULL;
 	DefElem    *dcollate = NULL;
 	DefElem    *dctype = NULL;
+	DefElem	   *dcollprovider = NULL;
 	DefElem    *distemplate = NULL;
 	DefElem    *dallowconnections = NULL;
 	DefElem    *dconnlimit = NULL;
@@ -136,6 +140,7 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 	const char *dbtemplate = NULL;
 	char	   *dbcollate = NULL;
 	char	   *dbctype = NULL;
+	char		dbcollprovider = '\0';
 	char	   *canonname;
 	int			encoding = -1;
 	bool		dbistemplate = false;
@@ -213,6 +218,15 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 						 parser_errposition(pstate, defel->location)));
 			dctype = defel;
 		}
+		else if (strcmp(defel->defname, "collation_provider") == 0)
+		{
+			if (dcollprovider)
+				ereport(ERROR,
+						(errcode(ERRCODE_SYNTAX_ERROR),
+						 errmsg("conflicting or redundant options"),
+						 parser_errposition(pstate, defel->location)));
+			dcollprovider = defel;
+		}
 		else if (strcmp(defel->defname, "is_template") == 0)
 		{
 			if (distemplate)
@@ -302,6 +316,23 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 		dbcollate = defGetString(dcollate);
 	if (dctype && dctype->arg)
 		dbctype = defGetString(dctype);
+	if (dcollprovider && dcollprovider->arg)
+	{
+		char	   *collproviderstr = defGetString(dcollprovider);
+
+#ifdef USE_ICU
+		if (pg_strcasecmp(collproviderstr, "icu") == 0)
+			dbcollprovider = COLLPROVIDER_ICU;
+		else
+#endif
+		if (pg_strcasecmp(collproviderstr, "libc") == 0)
+			dbcollprovider = COLLPROVIDER_LIBC;
+		else
+			ereport(ERROR,
+					(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
+					 errmsg("unrecognized collation provider: %s",
+							collproviderstr)));
+	}
 	if (distemplate && distemplate->arg)
 		dbistemplate = defGetBoolean(distemplate);
 	if (dallowconnections && dallowconnections->arg)
@@ -351,7 +382,7 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 					 &src_dboid, &src_owner, &src_encoding,
 					 &src_istemplate, &src_allowconn, &src_lastsysoid,
 					 &src_frozenxid, &src_minmxid, &src_deftablespace,
-					 &src_collate, &src_ctype))
+					 &src_collate, &src_ctype, &src_collprovider))
 		ereport(ERROR,
 				(errcode(ERRCODE_UNDEFINED_DATABASE),
 				 errmsg("template database \"%s\" does not exist",
@@ -377,6 +408,8 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 		dbcollate = src_collate;
 	if (dbctype == NULL)
 		dbctype = src_ctype;
+	if (dbcollprovider == '\0')
+		dbcollprovider = src_collprovider;
 
 	/* Some encodings are client only */
 	if (!PG_VALID_BE_ENCODING(encoding))
@@ -384,6 +417,8 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 				(errcode(ERRCODE_WRONG_OBJECT_TYPE),
 				 errmsg("invalid server encoding %d", encoding)));
 
+	if (dbcollprovider == COLLPROVIDER_LIBC)
+	{
 	/* Check that the chosen locales are valid, and get canonical spellings */
 	if (!check_locale(LC_COLLATE, dbcollate, &canonname))
 		ereport(ERROR,
@@ -397,6 +432,7 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 	dbctype = canonname;
 
 	check_encoding_locale_matches(encoding, dbcollate, dbctype);
+	}
 
 	/*
 	 * Check that the new encoding and locale settings match the source
@@ -560,6 +596,7 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 		DirectFunctionCall1(namein, CStringGetDatum(dbcollate));
 	new_record[Anum_pg_database_datctype - 1] =
 		DirectFunctionCall1(namein, CStringGetDatum(dbctype));
+	new_record[Anum_pg_database_datcollprovider - 1] = CharGetDatum(dbcollprovider);
 	new_record[Anum_pg_database_datistemplate - 1] = BoolGetDatum(dbistemplate);
 	new_record[Anum_pg_database_datallowconn - 1] = BoolGetDatum(dballowconnections);
 	new_record[Anum_pg_database_datconnlimit - 1] = Int32GetDatum(dbconnlimit);
@@ -833,7 +870,7 @@ dropdb(const char *dbname, bool missing_ok)
 	pgdbrel = table_open(DatabaseRelationId, RowExclusiveLock);
 
 	if (!get_db_info(dbname, AccessExclusiveLock, &db_id, NULL, NULL,
-					 &db_istemplate, NULL, NULL, NULL, NULL, NULL, NULL, NULL))
+					 &db_istemplate, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL))
 	{
 		if (!missing_ok)
 		{
@@ -1024,7 +1061,7 @@ RenameDatabase(const char *oldname, const char *newname)
 	rel = table_open(DatabaseRelationId, RowExclusiveLock);
 
 	if (!get_db_info(oldname, AccessExclusiveLock, &db_id, NULL, NULL,
-					 NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL))
+					 NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL))
 		ereport(ERROR,
 				(errcode(ERRCODE_UNDEFINED_DATABASE),
 				 errmsg("database \"%s\" does not exist", oldname)));
@@ -1137,7 +1174,7 @@ movedb(const char *dbname, const char *tblspcname)
 	pgdbrel = table_open(DatabaseRelationId, RowExclusiveLock);
 
 	if (!get_db_info(dbname, AccessExclusiveLock, &db_id, NULL, NULL,
-					 NULL, NULL, NULL, NULL, NULL, &src_tblspcoid, NULL, NULL))
+					 NULL, NULL, NULL, NULL, NULL, &src_tblspcoid, NULL, NULL, NULL))
 		ereport(ERROR,
 				(errcode(ERRCODE_UNDEFINED_DATABASE),
 				 errmsg("database \"%s\" does not exist", dbname)));
@@ -1769,7 +1806,8 @@ get_db_info(const char *name, LOCKMODE lockmode,
 			int *encodingP, bool *dbIsTemplateP, bool *dbAllowConnP,
 			Oid *dbLastSysOidP, TransactionId *dbFrozenXidP,
 			MultiXactId *dbMinMultiP,
-			Oid *dbTablespace, char **dbCollate, char **dbCtype)
+			Oid *dbTablespace, char **dbCollate, char **dbCtype,
+			char *dbCollProvider)
 {
 	bool		result = false;
 	Relation	relation;
@@ -1866,6 +1904,8 @@ get_db_info(const char *name, LOCKMODE lockmode,
 					*dbCollate = pstrdup(NameStr(dbform->datcollate));
 				if (dbCtype)
 					*dbCtype = pstrdup(NameStr(dbform->datctype));
+				if (dbCollProvider)
+					*dbCollProvider = dbform->datcollprovider;
 				ReleaseSysCache(tuple);
 				result = true;
 				break;
diff --git a/src/backend/regex/regc_pg_locale.c b/src/backend/regex/regc_pg_locale.c
index 4a808b7606..510bd71371 100644
--- a/src/backend/regex/regc_pg_locale.c
+++ b/src/backend/regex/regc_pg_locale.c
@@ -241,7 +241,12 @@ pg_set_regex_collation(Oid collation)
 	else
 	{
 		if (collation == DEFAULT_COLLATION_OID)
-			pg_regex_locale = 0;
+		{
+			if (global_locale.provider == COLLPROVIDER_ICU)
+				pg_regex_locale = &global_locale;
+			else
+				pg_regex_locale = 0;
+		}
 		else if (OidIsValid(collation))
 		{
 			/*
diff --git a/src/backend/utils/adt/formatting.c b/src/backend/utils/adt/formatting.c
index f7175df8da..dca8ca566f 100644
--- a/src/backend/utils/adt/formatting.c
+++ b/src/backend/utils/adt/formatting.c
@@ -1674,6 +1674,8 @@ str_tolower(const char *buff, size_t nbytes, Oid collid)
 			}
 			mylocale = pg_newlocale_from_collation(collid);
 		}
+		else if (global_locale.provider == COLLPROVIDER_ICU)
+			mylocale = &global_locale;
 
 #ifdef USE_ICU
 		if (mylocale && mylocale->provider == COLLPROVIDER_ICU)
@@ -1798,6 +1800,8 @@ str_toupper(const char *buff, size_t nbytes, Oid collid)
 			}
 			mylocale = pg_newlocale_from_collation(collid);
 		}
+		else if (global_locale.provider == COLLPROVIDER_ICU)
+			mylocale = &global_locale;
 
 #ifdef USE_ICU
 		if (mylocale && mylocale->provider == COLLPROVIDER_ICU)
@@ -1923,6 +1927,8 @@ str_initcap(const char *buff, size_t nbytes, Oid collid)
 			}
 			mylocale = pg_newlocale_from_collation(collid);
 		}
+		else if (global_locale.provider == COLLPROVIDER_ICU)
+			mylocale = &global_locale;
 
 #ifdef USE_ICU
 		if (mylocale && mylocale->provider == COLLPROVIDER_ICU)
diff --git a/src/backend/utils/adt/like.c b/src/backend/utils/adt/like.c
index 13d5cb083c..57dd3fe59d 100644
--- a/src/backend/utils/adt/like.c
+++ b/src/backend/utils/adt/like.c
@@ -150,9 +150,14 @@ SB_lower_char(unsigned char c, pg_locale_t locale, bool locale_is_c)
 static inline int
 GenericMatchText(const char *s, int slen, const char *p, int plen, Oid collation)
 {
-	if (collation && !lc_ctype_is_c(collation) && collation != DEFAULT_COLLATION_OID)
+	if (collation && !lc_ctype_is_c(collation))
 	{
-		pg_locale_t locale = pg_newlocale_from_collation(collation);
+		pg_locale_t locale = 0;
+
+		if (collation != DEFAULT_COLLATION_OID)
+			locale = pg_newlocale_from_collation(collation);
+		else if (global_locale.provider == COLLPROVIDER_ICU)
+			locale = &global_locale;
 
 		if (locale && !locale->deterministic)
 			ereport(ERROR,
@@ -195,11 +200,14 @@ Generic_Text_IC_like(text *str, text *pat, Oid collation)
 		}
 		locale = pg_newlocale_from_collation(collation);
 
-		if (locale && !locale->deterministic)
-			ereport(ERROR,
-					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-					 errmsg("nondeterministic collations are not supported for ILIKE")));
 	}
+	else if (global_locale.provider == COLLPROVIDER_ICU)
+		locale = &global_locale;
+
+	if (locale && !locale->deterministic)
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				 errmsg("nondeterministic collations are not supported for ILIKE")));
 
 	/*
 	 * For efficiency reasons, in the single byte case we don't call lower()
diff --git a/src/backend/utils/adt/like_support.c b/src/backend/utils/adt/like_support.c
index c8fec7863f..09a28aab8e 100644
--- a/src/backend/utils/adt/like_support.c
+++ b/src/backend/utils/adt/like_support.c
@@ -966,6 +966,8 @@ like_fixed_prefix(Const *patt_const, bool case_insensitive, Oid collation,
 			}
 			locale = pg_newlocale_from_collation(collation);
 		}
+		else if (global_locale.provider == COLLPROVIDER_ICU)
+			locale = &global_locale;
 	}
 
 	if (typeid != BYTEAOID)
diff --git a/src/backend/utils/adt/pg_locale.c b/src/backend/utils/adt/pg_locale.c
index fcdbaae37b..5a2cbc7dfb 100644
--- a/src/backend/utils/adt/pg_locale.c
+++ b/src/backend/utils/adt/pg_locale.c
@@ -1191,6 +1191,9 @@ lc_collate_is_c(Oid collation)
 		static int	result = -1;
 		char	   *localeptr;
 
+		if (global_locale.provider == COLLPROVIDER_ICU)
+			return false;
+
 		if (result >= 0)
 			return (bool) result;
 		localeptr = setlocale(LC_COLLATE, NULL);
@@ -1241,6 +1244,9 @@ lc_ctype_is_c(Oid collation)
 		static int	result = -1;
 		char	   *localeptr;
 
+		if (global_locale.provider == COLLPROVIDER_ICU)
+			return false;
+
 		if (result >= 0)
 			return (bool) result;
 		localeptr = setlocale(LC_CTYPE, NULL);
@@ -1269,6 +1275,89 @@ lc_ctype_is_c(Oid collation)
 	return (lookup_collation_cache(collation, true))->ctype_is_c;
 }
 
+struct pg_locale_struct global_locale;
+
+void
+make_icu_collator(const char *collcollate, const char *collctype,
+				  struct pg_locale_struct *resultp)
+{
+#ifdef USE_ICU
+	UCollator  *collator;
+	UErrorCode	status;
+
+	if (strcmp(collcollate, collctype) != 0)
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				 errmsg("collations with different collate and ctype values are not supported by ICU")));
+
+	status = U_ZERO_ERROR;
+	collator = ucol_open(collcollate, &status);
+	if (U_FAILURE(status))
+		ereport(ERROR,
+				(errmsg("could not open collator for locale \"%s\": %s",
+						collcollate, u_errorName(status))));
+
+	if (U_ICU_VERSION_MAJOR_NUM < 54)
+		icu_set_collation_attributes(collator, collcollate);
+
+	/* We will leak this string if we get an error below :-( */
+	resultp->info.icu.locale = MemoryContextStrdup(TopMemoryContext,
+														   collcollate);
+	resultp->info.icu.ucol = collator;
+#else							/* not USE_ICU */
+	/* could get here if a collation was created by a build with ICU */
+	ereport(ERROR,
+			(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+			 errmsg("ICU is not supported in this build"), \
+			 errhint("You need to rebuild PostgreSQL using --with-icu.")));
+#endif							/* not USE_ICU */
+}
+
+void
+check_collation_version(HeapTuple colltuple)
+{
+	Form_pg_collation collform;
+	Datum		collversion;
+	bool		isnull;
+
+	collform = (Form_pg_collation) GETSTRUCT(colltuple);
+
+	collversion = SysCacheGetAttr(COLLOID, colltuple, Anum_pg_collation_collversion,
+								  &isnull);
+	if (!isnull)
+	{
+		char	   *actual_versionstr;
+		char	   *collversionstr;
+
+		actual_versionstr = get_collation_actual_version(collform->collprovider,
+														 NameStr(collform->collcollate));
+		if (!actual_versionstr)
+		{
+			/*
+			 * This could happen when specifying a version in CREATE
+			 * COLLATION for a libc locale, or manually creating a mess in
+			 * the catalogs.
+			 */
+			ereport(ERROR,
+					(errmsg("collation \"%s\" has no actual version, but a version was specified",
+							NameStr(collform->collname))));
+		}
+		collversionstr = TextDatumGetCString(collversion);
+
+		if (strcmp(actual_versionstr, collversionstr) != 0)
+			ereport(WARNING,
+					(errmsg("collation \"%s\" has version mismatch",
+							NameStr(collform->collname)),
+					 errdetail("The collation in the database was created using version %s, "
+							   "but the operating system provides version %s.",
+							   collversionstr, actual_versionstr),
+					 errhint("Rebuild all objects affected by this collation and run "
+							 "ALTER COLLATION %s REFRESH VERSION, "
+							 "or build PostgreSQL with the right library version.",
+							 quote_qualified_identifier(get_namespace_name(collform->collnamespace),
+														NameStr(collform->collname)))));
+	}
+}
 
 /* simple subroutine for reporting errors from newlocale() */
 #ifdef HAVE_LOCALE_T
@@ -1342,8 +1431,6 @@ pg_newlocale_from_collation(Oid collid)
 		const char *collctype pg_attribute_unused();
 		struct pg_locale_struct result;
 		pg_locale_t resultp;
-		Datum		collversion;
-		bool		isnull;
 
 		tp = SearchSysCache1(COLLOID, ObjectIdGetDatum(collid));
 		if (!HeapTupleIsValid(tp))
@@ -1413,72 +1500,10 @@ pg_newlocale_from_collation(Oid collid)
 		}
 		else if (collform->collprovider == COLLPROVIDER_ICU)
 		{
-#ifdef USE_ICU
-			UCollator  *collator;
-			UErrorCode	status;
-
-			if (strcmp(collcollate, collctype) != 0)
-				ereport(ERROR,
-						(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-						 errmsg("collations with different collate and ctype values are not supported by ICU")));
-
-			status = U_ZERO_ERROR;
-			collator = ucol_open(collcollate, &status);
-			if (U_FAILURE(status))
-				ereport(ERROR,
-						(errmsg("could not open collator for locale \"%s\": %s",
-								collcollate, u_errorName(status))));
-
-			if (U_ICU_VERSION_MAJOR_NUM < 54)
-				icu_set_collation_attributes(collator, collcollate);
-
-			/* We will leak this string if we get an error below :-( */
-			result.info.icu.locale = MemoryContextStrdup(TopMemoryContext,
-														 collcollate);
-			result.info.icu.ucol = collator;
-#else							/* not USE_ICU */
-			/* could get here if a collation was created by a build with ICU */
-			ereport(ERROR,
-					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-					 errmsg("ICU is not supported in this build"), \
-					 errhint("You need to rebuild PostgreSQL using --with-icu.")));
-#endif							/* not USE_ICU */
+			make_icu_collator(collcollate, collctype, &result);
 		}
 
-		collversion = SysCacheGetAttr(COLLOID, tp, Anum_pg_collation_collversion,
-									  &isnull);
-		if (!isnull)
-		{
-			char	   *actual_versionstr;
-			char	   *collversionstr;
-
-			actual_versionstr = get_collation_actual_version(collform->collprovider, collcollate);
-			if (!actual_versionstr)
-			{
-				/*
-				 * This could happen when specifying a version in CREATE
-				 * COLLATION for a libc locale, or manually creating a mess in
-				 * the catalogs.
-				 */
-				ereport(ERROR,
-						(errmsg("collation \"%s\" has no actual version, but a version was specified",
-								NameStr(collform->collname))));
-			}
-			collversionstr = TextDatumGetCString(collversion);
-
-			if (strcmp(actual_versionstr, collversionstr) != 0)
-				ereport(WARNING,
-						(errmsg("collation \"%s\" has version mismatch",
-								NameStr(collform->collname)),
-						 errdetail("The collation in the database was created using version %s, "
-								   "but the operating system provides version %s.",
-								   collversionstr, actual_versionstr),
-						 errhint("Rebuild all objects affected by this collation and run "
-								 "ALTER COLLATION %s REFRESH VERSION, "
-								 "or build PostgreSQL with the right library version.",
-								 quote_qualified_identifier(get_namespace_name(collform->collnamespace),
-															NameStr(collform->collname)))));
-		}
+		check_collation_version(tp);
 
 		ReleaseSysCache(tp);
 
@@ -1505,6 +1530,13 @@ get_collation_actual_version(char collprovider, const char *collcollate)
 {
 	char	   *collversion = NULL;
 
+	if (collprovider == COLLPROVIDER_DEFAULT)
+	{
+		/* Recurse to the real provider. */
+		collversion = get_collation_actual_version(global_locale.provider,
+												   global_locale.info.icu.locale);
+	}
+	else
 #ifdef USE_ICU
 	if (collprovider == COLLPROVIDER_ICU)
 	{
diff --git a/src/backend/utils/adt/varchar.c b/src/backend/utils/adt/varchar.c
index e63a4e553b..d1b6ccc6a3 100644
--- a/src/backend/utils/adt/varchar.c
+++ b/src/backend/utils/adt/varchar.c
@@ -751,7 +751,7 @@ bpchareq(PG_FUNCTION_ARGS)
 	len2 = bcTruelen(arg2);
 
 	if (lc_collate_is_c(collid) ||
-		collid == DEFAULT_COLLATION_OID ||
+		(collid == DEFAULT_COLLATION_OID && global_locale.deterministic) ||
 		pg_newlocale_from_collation(collid)->deterministic)
 	{
 		/*
@@ -789,7 +789,7 @@ bpcharne(PG_FUNCTION_ARGS)
 	len2 = bcTruelen(arg2);
 
 	if (lc_collate_is_c(collid) ||
-		collid == DEFAULT_COLLATION_OID ||
+		(collid == DEFAULT_COLLATION_OID && global_locale.deterministic) ||
 		pg_newlocale_from_collation(collid)->deterministic)
 	{
 		/*
@@ -995,8 +995,13 @@ hashbpchar(PG_FUNCTION_ARGS)
 	keydata = VARDATA_ANY(key);
 	keylen = bcTruelen(key);
 
-	if (!lc_collate_is_c(collid) && collid != DEFAULT_COLLATION_OID)
-		mylocale = pg_newlocale_from_collation(collid);
+	if (!lc_collate_is_c(collid))
+	{
+		if (collid != DEFAULT_COLLATION_OID)
+			mylocale = pg_newlocale_from_collation(collid);
+		else if (global_locale.provider == COLLPROVIDER_ICU)
+			mylocale = &global_locale;
+	}
 
 	if (!mylocale || mylocale->deterministic)
 	{
@@ -1055,8 +1060,13 @@ hashbpcharextended(PG_FUNCTION_ARGS)
 	keydata = VARDATA_ANY(key);
 	keylen = bcTruelen(key);
 
-	if (!lc_collate_is_c(collid) && collid != DEFAULT_COLLATION_OID)
-		mylocale = pg_newlocale_from_collation(collid);
+	if (!lc_collate_is_c(collid))
+	{
+		if (collid != DEFAULT_COLLATION_OID)
+			mylocale = pg_newlocale_from_collation(collid);
+		else if (global_locale.provider == COLLPROVIDER_ICU)
+			mylocale = &global_locale;
+	}
 
 	if (!mylocale || mylocale->deterministic)
 	{
diff --git a/src/backend/utils/adt/varlena.c b/src/backend/utils/adt/varlena.c
index 722b2c722d..0543a0688c 100644
--- a/src/backend/utils/adt/varlena.c
+++ b/src/backend/utils/adt/varlena.c
@@ -1156,8 +1156,13 @@ text_position_setup(text *t1, text *t2, Oid collid, TextPositionState *state)
 
 	check_collation_set(collid);
 
-	if (!lc_collate_is_c(collid) && collid != DEFAULT_COLLATION_OID)
-		mylocale = pg_newlocale_from_collation(collid);
+	if (!lc_collate_is_c(collid))
+	{
+		if (collid != DEFAULT_COLLATION_OID)
+			mylocale = pg_newlocale_from_collation(collid);
+		else if (global_locale.provider == COLLPROVIDER_ICU)
+			mylocale = &global_locale;
+	}
 
 	if (mylocale && !mylocale->deterministic)
 		ereport(ERROR,
@@ -1499,6 +1504,8 @@ varstr_cmp(const char *arg1, int len1, const char *arg2, int len2, Oid collid)
 
 		if (collid != DEFAULT_COLLATION_OID)
 			mylocale = pg_newlocale_from_collation(collid);
+		else if (global_locale.provider == COLLPROVIDER_ICU)
+			mylocale = &global_locale;
 
 		/*
 		 * memcmp() can't tell us which of two unequal strings sorts first,
@@ -1720,7 +1727,7 @@ texteq(PG_FUNCTION_ARGS)
 	check_collation_set(collid);
 
 	if (lc_collate_is_c(collid) ||
-		collid == DEFAULT_COLLATION_OID ||
+		(collid == DEFAULT_COLLATION_OID && global_locale.deterministic) ||
 		pg_newlocale_from_collation(collid)->deterministic)
 	{
 		Datum		arg1 = PG_GETARG_DATUM(0);
@@ -1774,7 +1781,7 @@ textne(PG_FUNCTION_ARGS)
 	check_collation_set(collid);
 
 	if (lc_collate_is_c(collid) ||
-		collid == DEFAULT_COLLATION_OID ||
+		(collid == DEFAULT_COLLATION_OID && global_locale.deterministic) ||
 		pg_newlocale_from_collation(collid)->deterministic)
 	{
 		Datum		arg1 = PG_GETARG_DATUM(0);
@@ -1886,8 +1893,13 @@ text_starts_with(PG_FUNCTION_ARGS)
 
 	check_collation_set(collid);
 
-	if (!lc_collate_is_c(collid) && collid != DEFAULT_COLLATION_OID)
-		mylocale = pg_newlocale_from_collation(collid);
+	if (!lc_collate_is_c(collid))
+	{
+		if (collid != DEFAULT_COLLATION_OID)
+			mylocale = pg_newlocale_from_collation(collid);
+		else if (global_locale.provider == COLLPROVIDER_ICU)
+			mylocale = &global_locale;
+	}
 
 	if (mylocale && !mylocale->deterministic)
 		ereport(ERROR,
@@ -2002,6 +2014,8 @@ varstr_sortsupport(SortSupport ssup, Oid typid, Oid collid)
 		 */
 		if (collid != DEFAULT_COLLATION_OID)
 			locale = pg_newlocale_from_collation(collid);
+		else if (global_locale.provider == COLLPROVIDER_ICU)
+			locale = &global_locale;
 
 		/*
 		 * There is a further exception on Windows.  When the database
diff --git a/src/backend/utils/init/postinit.c b/src/backend/utils/init/postinit.c
index 29c5ec7b58..1a91b42798 100644
--- a/src/backend/utils/init/postinit.c
+++ b/src/backend/utils/init/postinit.c
@@ -31,6 +31,7 @@
 #include "catalog/indexing.h"
 #include "catalog/namespace.h"
 #include "catalog/pg_authid.h"
+#include "catalog/pg_collation.h"
 #include "catalog/pg_database.h"
 #include "catalog/pg_db_role_setting.h"
 #include "catalog/pg_tablespace.h"
@@ -404,6 +405,8 @@ CheckMyDatabase(const char *name, bool am_superuser, bool override_allow_connect
 	collate = NameStr(dbform->datcollate);
 	ctype = NameStr(dbform->datctype);
 
+	if (dbform->datcollprovider == COLLPROVIDER_LIBC)
+	{
 	if (pg_perm_setlocale(LC_COLLATE, collate) == NULL)
 		ereport(FATAL,
 				(errmsg("database locale is incompatible with operating system"),
@@ -417,6 +420,24 @@ CheckMyDatabase(const char *name, bool am_superuser, bool override_allow_connect
 				 errdetail("The database was initialized with LC_CTYPE \"%s\", "
 						   " which is not recognized by setlocale().", ctype),
 				 errhint("Recreate the database with another locale or install the missing locale.")));
+	}
+	else if (dbform->datcollprovider == COLLPROVIDER_ICU)
+	{
+		make_icu_collator(collate, ctype, &global_locale);
+	}
+
+	global_locale.provider = dbform->datcollprovider;
+	global_locale.deterministic = true;	// TODO
+
+	{
+		HeapTuple	tp;
+
+		tp = SearchSysCache1(COLLOID, ObjectIdGetDatum(DEFAULT_COLLATION_OID));
+		if (!HeapTupleIsValid(tp))
+			elog(ERROR, "cache lookup failed for collation %u", DEFAULT_COLLATION_OID);
+		check_collation_version(tp);
+		ReleaseSysCache(tp);
+	}
 
 	/* Make the locale settings visible as GUC variables, too */
 	SetConfigOption("lc_collate", collate, PGC_INTERNAL, PGC_S_OVERRIDE);
diff --git a/src/bin/initdb/Makefile b/src/bin/initdb/Makefile
index 7c404430a9..a9335a8ba6 100644
--- a/src/bin/initdb/Makefile
+++ b/src/bin/initdb/Makefile
@@ -61,6 +61,8 @@ clean distclean maintainer-clean:
 # ensure that changes in datadir propagate into object file
 initdb.o: initdb.c $(top_builddir)/src/Makefile.global
 
+export with_icu
+
 check:
 	$(prove_check)
 
diff --git a/src/bin/initdb/initdb.c b/src/bin/initdb/initdb.c
index 88a261d9bd..62c310040a 100644
--- a/src/bin/initdb/initdb.c
+++ b/src/bin/initdb/initdb.c
@@ -129,6 +129,8 @@ static char *lc_monetary = NULL;
 static char *lc_numeric = NULL;
 static char *lc_time = NULL;
 static char *lc_messages = NULL;
+static char collation_provider[] = {COLLPROVIDER_LIBC, '\0'};
+static char *icu_locale = NULL;
 static const char *default_text_search_config = NULL;
 static char *username = NULL;
 static bool pwprompt = false;
@@ -1412,10 +1414,13 @@ bootstrap_template1(void)
 							  encodingid_to_string(encodingid));
 
 	bki_lines = replace_token(bki_lines, "LC_COLLATE",
-							  escape_quotes_bki(lc_collate));
+							  escape_quotes_bki(collation_provider[0] == COLLPROVIDER_ICU ? icu_locale : lc_collate));
 
 	bki_lines = replace_token(bki_lines, "LC_CTYPE",
-							  escape_quotes_bki(lc_ctype));
+							  escape_quotes_bki(collation_provider[0] == COLLPROVIDER_ICU ? icu_locale : lc_ctype));
+
+	bki_lines = replace_token(bki_lines, "COLLPROVIDER",
+							  collation_provider);
 
 	/* Also ensure backend isn't confused by this environment var: */
 	unsetenv("PGCLIENTENCODING");
@@ -1707,6 +1712,12 @@ setup_description(FILE *cmdfd)
 static void
 setup_collation(FILE *cmdfd)
 {
+	/*
+	 * Set version of the default collation.
+	 */
+	PG_CMD_PRINTF("UPDATE pg_collation SET collversion = pg_collation_actual_version(oid) WHERE oid = %d;\n\n",
+				  DEFAULT_COLLATION_OID);
+
 	/*
 	 * Add an SQL-standard name.  We don't want to pin this, so it doesn't go
 	 * in pg_collation.h.  But add it before reading system collations, so
@@ -1995,8 +2006,6 @@ make_template0(FILE *cmdfd)
 {
 	const char *const *line;
 	static const char *const template0_setup[] = {
-		"CREATE DATABASE template0 IS_TEMPLATE = true ALLOW_CONNECTIONS = false;\n\n",
-
 		/*
 		 * We use the OID of template0 to determine datlastsysoid
 		 */
@@ -2021,6 +2030,9 @@ make_template0(FILE *cmdfd)
 		NULL
 	};
 
+	PG_CMD_PRINTF("CREATE DATABASE template0 IS_TEMPLATE = true ALLOW_CONNECTIONS = false COLLATION_PROVIDER = %s;\n\n",
+				  collation_provider[0] == COLLPROVIDER_ICU ? "icu" : "libc");
+
 	for (line = template0_setup; *line; line++)
 		PG_CMD_PUTS(*line);
 }
@@ -2293,13 +2305,14 @@ setlocales(void)
 			lc_monetary = locale;
 		if (!lc_messages)
 			lc_messages = locale;
+		if (!icu_locale)
+			icu_locale = locale;
 	}
 
 	/*
 	 * canonicalize locale names, and obtain any missing values from our
 	 * current environment
 	 */
-
 	check_locale_name(LC_CTYPE, lc_ctype, &canonname);
 	lc_ctype = canonname;
 	check_locale_name(LC_COLLATE, lc_collate, &canonname);
@@ -2318,6 +2331,18 @@ setlocales(void)
 	check_locale_name(LC_CTYPE, lc_messages, &canonname);
 	lc_messages = canonname;
 #endif
+
+	/*
+	 * If ICU is selected but no ICU locale has been given, take the
+	 * lc_collate locale and chop off any encoding suffix.  This should give
+	 * the user a configuration that resembles their operating system's locale
+	 * setup.
+	 */
+	if (collation_provider[0] == COLLPROVIDER_ICU && !icu_locale)
+	{
+		icu_locale = pg_strdup(lc_collate);
+		icu_locale[strcspn(icu_locale, ".")] = '\0';
+	}
 }
 
 /*
@@ -2333,9 +2358,12 @@ usage(const char *progname)
 	printf(_("  -A, --auth=METHOD         default authentication method for local connections\n"));
 	printf(_("      --auth-host=METHOD    default authentication method for local TCP/IP connections\n"));
 	printf(_("      --auth-local=METHOD   default authentication method for local-socket connections\n"));
+	printf(_("      --collation-provider={libc|icu}\n"
+			 "                            set default collation provider for new databases\n"));
 	printf(_(" [-D, --pgdata=]DATADIR     location for this database cluster\n"));
 	printf(_("  -E, --encoding=ENCODING   set default encoding for new databases\n"));
 	printf(_("  -g, --allow-group-access  allow group read/execute on data directory\n"));
+	printf(_("      --icu-locale          set ICU locale for new databases\n"));
 	printf(_("      --locale=LOCALE       set default locale for new databases\n"));
 	printf(_("      --lc-collate=, --lc-ctype=, --lc-messages=LOCALE\n"
 			 "      --lc-monetary=, --lc-numeric=, --lc-time=LOCALE\n"
@@ -2510,7 +2538,8 @@ setup_locale_encoding(void)
 		strcmp(lc_ctype, lc_time) == 0 &&
 		strcmp(lc_ctype, lc_numeric) == 0 &&
 		strcmp(lc_ctype, lc_monetary) == 0 &&
-		strcmp(lc_ctype, lc_messages) == 0)
+		strcmp(lc_ctype, lc_messages) == 0 &&
+		(!icu_locale || strcmp(lc_ctype, icu_locale) == 0))
 		printf(_("The database cluster will be initialized with locale \"%s\".\n"), lc_ctype);
 	else
 	{
@@ -2527,9 +2556,13 @@ setup_locale_encoding(void)
 			   lc_monetary,
 			   lc_numeric,
 			   lc_time);
+		if (icu_locale)
+			printf(_("  ICU:      %s\n"), icu_locale);
 	}
 
-	if (!encoding)
+	if (!encoding && collation_provider[0] == COLLPROVIDER_ICU)
+		encodingid = PG_UTF8;
+	else if (!encoding)
 	{
 		int			ctype_enc;
 
@@ -3029,6 +3062,8 @@ main(int argc, char *argv[])
 		{"wal-segsize", required_argument, NULL, 12},
 		{"data-checksums", no_argument, NULL, 'k'},
 		{"allow-group-access", no_argument, NULL, 'g'},
+		{"collation-provider", required_argument, NULL, 13},
+		{"icu-locale", required_argument, NULL, 14},
 		{NULL, 0, NULL, 0}
 	};
 
@@ -3167,6 +3202,20 @@ main(int argc, char *argv[])
 			case 'g':
 				SetDataDirectoryCreatePerm(PG_DIR_MODE_GROUP);
 				break;
+			case 13:
+				if (strcmp(optarg, "icu") == 0)
+					collation_provider[0] = COLLPROVIDER_ICU;
+				else if (strcmp(optarg, "libc") == 0)
+					collation_provider[0] = COLLPROVIDER_LIBC;
+				else
+				{
+					pg_log_error("unrecognized collation provider: %s", optarg);
+					exit(1);
+				}
+				break;
+			case 14:
+				icu_locale = pg_strdup(optarg);
+				break;
 			default:
 				/* getopt_long already emitted a complaint */
 				fprintf(stderr, _("Try \"%s --help\" for more information.\n"),
diff --git a/src/bin/initdb/t/001_initdb.pl b/src/bin/initdb/t/001_initdb.pl
index 8387b945d3..90f6fc8f14 100644
--- a/src/bin/initdb/t/001_initdb.pl
+++ b/src/bin/initdb/t/001_initdb.pl
@@ -8,7 +8,7 @@ use Fcntl ':mode';
 use File::stat qw{lstat};
 use PostgresNode;
 use TestLib;
-use Test::More tests => 22;
+use Test::More tests => 24;
 
 my $tempdir = TestLib::tempdir;
 my $xlogdir = "$tempdir/pgxlog";
@@ -89,3 +89,19 @@ SKIP:
 	ok(check_mode_recursive($datadir_group, 0750, 0640),
 		'check PGDATA permissions');
 }
+
+# Collation provider tests
+
+if ($ENV{with_icu} eq 'yes')
+{
+	command_ok(['initdb', '--no-sync', '--collation-provider=icu', "$tempdir/data2"],
+			   'collation provider ICU');
+}
+else
+{
+	command_fails(['initdb', '--no-sync', '--collation-provider=icu', "$tempdir/data2"],
+				  'collation provider ICU fails since no ICU support');
+}
+
+command_fails(['initdb', '--no-sync', '--collation-provider=xyz', "$tempdir/dataX"],
+			  'fails for invalid collation provider');
diff --git a/src/bin/pg_dump/pg_dump.c b/src/bin/pg_dump/pg_dump.c
index f01fea5b91..9d7842583b 100644
--- a/src/bin/pg_dump/pg_dump.c
+++ b/src/bin/pg_dump/pg_dump.c
@@ -2638,6 +2638,7 @@ dumpDatabase(Archive *fout)
 				i_datname,
 				i_dba,
 				i_encoding,
+				i_datcollprovider,
 				i_collate,
 				i_ctype,
 				i_frozenxid,
@@ -2652,6 +2653,7 @@ dumpDatabase(Archive *fout)
 	const char *datname,
 			   *dba,
 			   *encoding,
+			   *datcollprovider,
 			   *collate,
 			   *ctype,
 			   *datacl,
@@ -2680,6 +2682,7 @@ dumpDatabase(Archive *fout)
 		appendPQExpBuffer(dbQry, "SELECT tableoid, oid, datname, "
 						  "(%s datdba) AS dba, "
 						  "pg_encoding_to_char(encoding) AS encoding, "
+						  "datcollprovider, "
 						  "datcollate, datctype, datfrozenxid, datminmxid, "
 						  "(SELECT array_agg(acl ORDER BY row_n) FROM "
 						  "  (SELECT acl, row_n FROM "
@@ -2772,6 +2775,7 @@ dumpDatabase(Archive *fout)
 	i_datname = PQfnumber(res, "datname");
 	i_dba = PQfnumber(res, "dba");
 	i_encoding = PQfnumber(res, "encoding");
+	i_datcollprovider = PQfnumber(res, "datcollprovider");
 	i_collate = PQfnumber(res, "datcollate");
 	i_ctype = PQfnumber(res, "datctype");
 	i_frozenxid = PQfnumber(res, "datfrozenxid");
@@ -2787,6 +2791,7 @@ dumpDatabase(Archive *fout)
 	datname = PQgetvalue(res, 0, i_datname);
 	dba = PQgetvalue(res, 0, i_dba);
 	encoding = PQgetvalue(res, 0, i_encoding);
+	datcollprovider = PQgetvalue(res, 0, i_datcollprovider);
 	collate = PQgetvalue(res, 0, i_collate);
 	ctype = PQgetvalue(res, 0, i_ctype);
 	frozenxid = atooid(PQgetvalue(res, 0, i_frozenxid));
@@ -2812,6 +2817,17 @@ dumpDatabase(Archive *fout)
 		appendPQExpBufferStr(creaQry, " ENCODING = ");
 		appendStringLiteralAH(creaQry, encoding, fout);
 	}
+	if (strlen(datcollprovider) > 0)
+	{
+		appendPQExpBufferStr(creaQry, " COLLATION_PROVIDER = ");
+		if (datcollprovider[0] == 'c')
+			appendPQExpBufferStr(creaQry, "libc");
+		else if (datcollprovider[0] == 'i')
+			appendPQExpBufferStr(creaQry, "icu");
+		else
+			fatal("unrecognized collation provider: %s",
+				  datcollprovider);
+	}
 	if (strlen(collate) > 0 && strcmp(collate, ctype) == 0)
 	{
 		appendPQExpBufferStr(creaQry, " LOCALE = ");
diff --git a/src/bin/psql/describe.c b/src/bin/psql/describe.c
index d7c0fc0c1e..23fdbb92ae 100644
--- a/src/bin/psql/describe.c
+++ b/src/bin/psql/describe.c
@@ -880,6 +880,14 @@ listAllDbs(const char *pattern, bool verbose)
 						  "       d.datctype as \"%s\",\n",
 						  gettext_noop("Collate"),
 						  gettext_noop("Ctype"));
+	if (pset.sversion >= 130000)
+		appendPQExpBuffer(&buf,
+						  "       CASE d.datcollprovider WHEN 'c' THEN 'libc' WHEN 'i' THEN 'icu' END AS \"%s\",\n",
+						  gettext_noop("Provider"));
+	else
+		appendPQExpBuffer(&buf,
+						  "       'libc' AS \"%s\",\n",
+						  gettext_noop("Provider"));
 	appendPQExpBufferStr(&buf, "       ");
 	printACLColumn(&buf, "d.datacl");
 	if (verbose && pset.sversion >= 80200)
diff --git a/src/bin/scripts/Makefile b/src/bin/scripts/Makefile
index ede665090f..ef4f8593dc 100644
--- a/src/bin/scripts/Makefile
+++ b/src/bin/scripts/Makefile
@@ -53,6 +53,8 @@ clean distclean maintainer-clean:
 	rm -f common.o scripts_parallel.o $(WIN32RES)
 	rm -rf tmp_check
 
+export with_icu
+
 check:
 	$(prove_check)
 
diff --git a/src/bin/scripts/createdb.c b/src/bin/scripts/createdb.c
index 64bcc20cb4..5944fd3f63 100644
--- a/src/bin/scripts/createdb.c
+++ b/src/bin/scripts/createdb.c
@@ -37,6 +37,7 @@ main(int argc, char *argv[])
 		{"lc-ctype", required_argument, NULL, 2},
 		{"locale", required_argument, NULL, 'l'},
 		{"maintenance-db", required_argument, NULL, 3},
+		{"collation-provider", required_argument, NULL, 4},
 		{NULL, 0, NULL, 0}
 	};
 
@@ -59,6 +60,7 @@ main(int argc, char *argv[])
 	char	   *lc_collate = NULL;
 	char	   *lc_ctype = NULL;
 	char	   *locale = NULL;
+	char	   *collation_provider = NULL;
 
 	PQExpBufferData sql;
 
@@ -117,6 +119,9 @@ main(int argc, char *argv[])
 			case 3:
 				maintenance_db = pg_strdup(optarg);
 				break;
+			case 4:
+				collation_provider = pg_strdup(optarg);
+				break;
 			default:
 				fprintf(stderr, _("Try \"%s --help\" for more information.\n"), progname);
 				exit(1);
@@ -193,6 +198,8 @@ main(int argc, char *argv[])
 		appendPQExpBuffer(&sql, " LC_COLLATE '%s'", lc_collate);
 	if (lc_ctype)
 		appendPQExpBuffer(&sql, " LC_CTYPE '%s'", lc_ctype);
+	if (collation_provider)
+		appendPQExpBuffer(&sql, " COLLATION_PROVIDER %s", collation_provider);
 
 	appendPQExpBufferChar(&sql, ';');
 
@@ -250,6 +257,8 @@ help(const char *progname)
 	printf(_("Usage:\n"));
 	printf(_("  %s [OPTION]... [DBNAME] [DESCRIPTION]\n"), progname);
 	printf(_("\nOptions:\n"));
+	printf(_("      --collation-provider={libc|icu}\n"
+			 "                               collation provider for the database\n"));
 	printf(_("  -D, --tablespace=TABLESPACE  default tablespace for the database\n"));
 	printf(_("  -e, --echo                   show the commands being sent to the server\n"));
 	printf(_("  -E, --encoding=ENCODING      encoding for the database\n"));
diff --git a/src/bin/scripts/t/020_createdb.pl b/src/bin/scripts/t/020_createdb.pl
index c0f6067a92..9e8220335f 100644
--- a/src/bin/scripts/t/020_createdb.pl
+++ b/src/bin/scripts/t/020_createdb.pl
@@ -3,7 +3,7 @@ use warnings;
 
 use PostgresNode;
 use TestLib;
-use Test::More tests => 13;
+use Test::More tests => 16;
 
 program_help_ok('createdb');
 program_version_ok('createdb');
@@ -22,5 +22,22 @@ $node->issues_sql_like(
 	qr/statement: CREATE DATABASE foobar2 ENCODING 'LATIN1'/,
 	'create database with encoding');
 
+if ($ENV{with_icu} eq 'yes')
+{
+	$node->issues_sql_like(
+		[ 'createdb', '-T', 'template0', '--collation-provider=icu', 'foobar3' ],
+		qr/statement: CREATE DATABASE foobar3 .* COLLATION_PROVIDER icu/,
+		'create database with ICU');
+}
+else
+{
+	$node->command_fails(
+		[ 'createdb', '-T', 'template0', '--collation-provider=icu', 'foobar3' ],
+		'create database with ICU fails since no ICU support');
+	pass;
+}
+
 $node->command_fails([ 'createdb', 'foobar1' ],
 	'fails if database already exists');
+$node->command_fails([ 'createdb', '-T', 'template0', '--collation-provider=xyz', 'foobarX' ],
+	'fails for invalid collation provider');
diff --git a/src/include/catalog/pg_database.dat b/src/include/catalog/pg_database.dat
index 89bd75d024..f261cdd838 100644
--- a/src/include/catalog/pg_database.dat
+++ b/src/include/catalog/pg_database.dat
@@ -15,7 +15,7 @@
 { oid => '1', oid_symbol => 'TemplateDbOid',
   descr => 'default template for new databases',
   datname => 'template1', encoding => 'ENCODING', datcollate => 'LC_COLLATE',
-  datctype => 'LC_CTYPE', datistemplate => 't', datallowconn => 't',
+  datctype => 'LC_CTYPE', datcollprovider => 'COLLPROVIDER', datistemplate => 't', datallowconn => 't',
   datconnlimit => '-1', datlastsysoid => '0', datfrozenxid => '0',
   datminmxid => '1', dattablespace => 'pg_default', datacl => '_null_' },
 
diff --git a/src/include/catalog/pg_database.h b/src/include/catalog/pg_database.h
index 06fea45f53..ab3c0951df 100644
--- a/src/include/catalog/pg_database.h
+++ b/src/include/catalog/pg_database.h
@@ -46,6 +46,9 @@ CATALOG(pg_database,1262,DatabaseRelationId) BKI_SHARED_RELATION BKI_ROWTYPE_OID
 	/* LC_CTYPE setting */
 	NameData	datctype;
 
+	/* see pg_collation.collprovider */
+	char		datcollprovider;
+
 	/* allowed as CREATE DATABASE template? */
 	bool		datistemplate;
 
diff --git a/src/include/utils/pg_locale.h b/src/include/utils/pg_locale.h
index b4b3aa5843..17fcee1e89 100644
--- a/src/include/utils/pg_locale.h
+++ b/src/include/utils/pg_locale.h
@@ -101,6 +101,12 @@ struct pg_locale_struct
 
 typedef struct pg_locale_struct *pg_locale_t;
 
+extern struct pg_locale_struct global_locale;
+
+extern void make_icu_collator(const char *collcollate, const char *collctype,
+							  struct pg_locale_struct *resultp);
+extern void check_collation_version(HeapTuple colltuple);
+
 extern pg_locale_t pg_newlocale_from_collation(Oid collid);
 
 extern char *get_collation_actual_version(char collprovider, const char *collcollate);
-- 
2.20.1

From 4eb9fbac238c1abf481fa43431ecc22e782a5290 Mon Sep 17 00:00:00 2001
From: Peter Eisentraut <peter@eisentraut.org>
Date: Thu, 30 Dec 2021 12:47:24 +0100
Subject: [PATCH v3] Add option to use ICU as global collation provider

This adds the option to use ICU as the default collation provider for
either the whole cluster or a database.  New options for initdb,
createdb, and CREATE DATABASE are used to select this.

Discussion: https://www.postgresql.org/message-id/flat/5e756dd6-0e91-d778-96fd-b1bcb06c161a%402ndquadrant.com
---
 doc/src/sgml/catalogs.sgml                    |  13 +-
 doc/src/sgml/ref/create_database.sgml         |  16 ++
 doc/src/sgml/ref/createdb.sgml                |   9 +
 doc/src/sgml/ref/initdb.sgml                  |  23 ++
 src/backend/access/hash/hashfunc.c            |  18 +-
 src/backend/catalog/pg_collation.c            |  24 +-
 src/backend/commands/collationcmds.c          | 120 +++++++---
 src/backend/commands/dbcommands.c             |  93 ++++++--
 src/backend/regex/regc_pg_locale.c            |   7 +-
 src/backend/utils/adt/formatting.c            |   6 +
 src/backend/utils/adt/like.c                  |  20 +-
 src/backend/utils/adt/like_support.c          |   2 +
 src/backend/utils/adt/pg_locale.c             | 223 +++++++++++-------
 src/backend/utils/adt/varchar.c               |  22 +-
 src/backend/utils/adt/varlena.c               |  26 +-
 src/backend/utils/init/postinit.c             |  37 ++-
 src/bin/initdb/Makefile                       |   2 +
 src/bin/initdb/initdb.c                       |  62 ++++-
 src/bin/initdb/t/001_initdb.pl                |  18 +-
 src/bin/pg_dump/pg_dump.c                     |  16 ++
 src/bin/psql/describe.c                       |  23 +-
 src/bin/psql/tab-complete.c                   |   2 +-
 src/bin/scripts/Makefile                      |   2 +
 src/bin/scripts/createdb.c                    |   9 +
 src/bin/scripts/t/020_createdb.pl             |  20 +-
 src/include/catalog/pg_collation.dat          |   3 +-
 src/include/catalog/pg_collation.h            |   6 +-
 src/include/catalog/pg_database.dat           |   2 +-
 src/include/catalog/pg_database.h             |  16 +-
 src/include/utils/pg_locale.h                 |   6 +
 .../regress/expected/collate.icu.utf8.out     |  10 +-
 src/test/regress/sql/collate.icu.utf8.sql     |   8 +-
 32 files changed, 665 insertions(+), 199 deletions(-)

diff --git a/doc/src/sgml/catalogs.sgml b/doc/src/sgml/catalogs.sgml
index 03e2537b07..89e7279030 100644
--- a/doc/src/sgml/catalogs.sgml
+++ b/doc/src/sgml/catalogs.sgml
@@ -2368,7 +2368,7 @@ <title><structname>pg_collation</structname> Columns</title>
 
      <row>
       <entry role="catalog_table_entry"><para role="column_definition">
-       <structfield>collcollate</structfield> <type>name</type>
+       <structfield>collcollate</structfield> <type>text</type>
       </para>
       <para>
        <symbol>LC_COLLATE</symbol> for this collation object
@@ -2377,13 +2377,22 @@ <title><structname>pg_collation</structname> Columns</title>
 
      <row>
       <entry role="catalog_table_entry"><para role="column_definition">
-       <structfield>collctype</structfield> <type>name</type>
+       <structfield>collctype</structfield> <type>text</type>
       </para>
       <para>
        <symbol>LC_CTYPE</symbol> for this collation object
       </para></entry>
      </row>
 
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
+       <structfield>collicucoll</structfield> <type>text</type>
+      </para>
+      <para>
+       ICU collation string
+      </para></entry>
+     </row>
+
      <row>
       <entry role="catalog_table_entry"><para role="column_definition">
        <structfield>collversion</structfield> <type>text</type>
diff --git a/doc/src/sgml/ref/create_database.sgml b/doc/src/sgml/ref/create_database.sgml
index 41cb4068ec..7374a9fad5 100644
--- a/doc/src/sgml/ref/create_database.sgml
+++ b/doc/src/sgml/ref/create_database.sgml
@@ -28,6 +28,7 @@
            [ LOCALE [=] <replaceable class="parameter">locale</replaceable> ]
            [ LC_COLLATE [=] <replaceable class="parameter">lc_collate</replaceable> ]
            [ LC_CTYPE [=] <replaceable class="parameter">lc_ctype</replaceable> ]
+           [ COLLATION_PROVIDER [=] <replaceable class="parameter">collation_provider</replaceable> ]
            [ TABLESPACE [=] <replaceable class="parameter">tablespace_name</replaceable> ]
            [ ALLOW_CONNECTIONS [=] <replaceable class="parameter">allowconn</replaceable> ]
            [ CONNECTION LIMIT [=] <replaceable class="parameter">connlimit</replaceable> ]
@@ -157,6 +158,21 @@ <title>Parameters</title>
        </para>
       </listitem>
      </varlistentry>
+
+     <varlistentry>
+      <term><replaceable>collation_provider</replaceable></term>
+
+      <listitem>
+       <para>
+        Specifies the provider to use for the default collation in this
+        database.  Possible values are:
+        <literal>icu</literal>,<indexterm><primary>ICU</primary></indexterm>
+        <literal>libc</literal>.  <literal>libc</literal> is the default.  The
+        available choices depend on the operating system and build options.
+       </para>
+      </listitem>
+     </varlistentry>
+
      <varlistentry>
       <term><replaceable class="parameter">tablespace_name</replaceable></term>
       <listitem>
diff --git a/doc/src/sgml/ref/createdb.sgml b/doc/src/sgml/ref/createdb.sgml
index 86473455c9..4b07363fcc 100644
--- a/doc/src/sgml/ref/createdb.sgml
+++ b/doc/src/sgml/ref/createdb.sgml
@@ -83,6 +83,15 @@ <title>Options</title>
       </listitem>
      </varlistentry>
 
+     <varlistentry>
+      <term><option>--collation-provider={<literal>libc</literal>|<literal>icu</literal>}</option></term>
+      <listitem>
+       <para>
+        Specifies the collation provider for the database's default collation.
+       </para>
+      </listitem>
+     </varlistentry>
+
      <varlistentry>
       <term><option>-D <replaceable class="parameter">tablespace</replaceable></option></term>
       <term><option>--tablespace=<replaceable class="parameter">tablespace</replaceable></option></term>
diff --git a/doc/src/sgml/ref/initdb.sgml b/doc/src/sgml/ref/initdb.sgml
index 8f71c7c962..77618d9a7a 100644
--- a/doc/src/sgml/ref/initdb.sgml
+++ b/doc/src/sgml/ref/initdb.sgml
@@ -166,6 +166,18 @@ <title>Options</title>
       </listitem>
      </varlistentry>
 
+     <varlistentry>
+      <term><option>--collation-provider={<literal>libc</literal>|<literal>icu</literal>}</option></term>
+      <listitem>
+       <para>
+        This option sets the collation provider for databases created in the
+        new cluster.  It can be overridden in the <command>CREATE
+        DATABASE</command> command when new databases are subsequently
+        created.  The default is <literal>libc</literal>.
+       </para>
+      </listitem>
+     </varlistentry>
+
      <varlistentry>
       <term><option>-D <replaceable class="parameter">directory</replaceable></option></term>
       <term><option>--pgdata=<replaceable class="parameter">directory</replaceable></option></term>
@@ -210,6 +222,17 @@ <title>Options</title>
       </listitem>
      </varlistentry>
 
+     <varlistentry>
+      <term><option>--icu-locale=<replaceable>locale</replaceable></option></term>
+      <listitem>
+       <para>
+        Specifies the ICU locale if the ICU collation provider is used.  If
+        this is not specified, the value from the <option>--locale</option>
+        option is used.
+       </para>
+      </listitem>
+     </varlistentry>
+
      <varlistentry id="app-initdb-data-checksums" xreflabel="data checksums">
       <term><option>-k</option></term>
       <term><option>--data-checksums</option></term>
diff --git a/src/backend/access/hash/hashfunc.c b/src/backend/access/hash/hashfunc.c
index 242333920e..6c29816193 100644
--- a/src/backend/access/hash/hashfunc.c
+++ b/src/backend/access/hash/hashfunc.c
@@ -278,8 +278,13 @@ hashtext(PG_FUNCTION_ARGS)
 				 errmsg("could not determine which collation to use for string hashing"),
 				 errhint("Use the COLLATE clause to set the collation explicitly.")));
 
-	if (!lc_collate_is_c(collid) && collid != DEFAULT_COLLATION_OID)
-		mylocale = pg_newlocale_from_collation(collid);
+	if (!lc_collate_is_c(collid))
+	{
+		if (collid != DEFAULT_COLLATION_OID)
+			mylocale = pg_newlocale_from_collation(collid);
+		else if (default_locale.provider == COLLPROVIDER_ICU)
+			mylocale = &default_locale;
+	}
 
 	if (!mylocale || mylocale->deterministic)
 	{
@@ -334,8 +339,13 @@ hashtextextended(PG_FUNCTION_ARGS)
 				 errmsg("could not determine which collation to use for string hashing"),
 				 errhint("Use the COLLATE clause to set the collation explicitly.")));
 
-	if (!lc_collate_is_c(collid) && collid != DEFAULT_COLLATION_OID)
-		mylocale = pg_newlocale_from_collation(collid);
+	if (!lc_collate_is_c(collid))
+	{
+		if (collid != DEFAULT_COLLATION_OID)
+			mylocale = pg_newlocale_from_collation(collid);
+		else if (default_locale.provider == COLLPROVIDER_ICU)
+			mylocale = &default_locale;
+	}
 
 	if (!mylocale || mylocale->deterministic)
 	{
diff --git a/src/backend/catalog/pg_collation.c b/src/backend/catalog/pg_collation.c
index 19068b652a..c3365e99c3 100644
--- a/src/backend/catalog/pg_collation.c
+++ b/src/backend/catalog/pg_collation.c
@@ -49,6 +49,7 @@ CollationCreate(const char *collname, Oid collnamespace,
 				bool collisdeterministic,
 				int32 collencoding,
 				const char *collcollate, const char *collctype,
+				const char *collicucoll,
 				const char *collversion,
 				bool if_not_exists,
 				bool quiet)
@@ -58,9 +59,7 @@ CollationCreate(const char *collname, Oid collnamespace,
 	HeapTuple	tup;
 	Datum		values[Natts_pg_collation];
 	bool		nulls[Natts_pg_collation];
-	NameData	name_name,
-				name_collate,
-				name_ctype;
+	NameData	name_name;
 	Oid			oid;
 	ObjectAddress myself,
 				referenced;
@@ -68,8 +67,7 @@ CollationCreate(const char *collname, Oid collnamespace,
 	AssertArg(collname);
 	AssertArg(collnamespace);
 	AssertArg(collowner);
-	AssertArg(collcollate);
-	AssertArg(collctype);
+	AssertArg((collcollate && collctype) || collicucoll);
 
 	/*
 	 * Make sure there is no existing collation of same name & encoding.
@@ -163,10 +161,18 @@ CollationCreate(const char *collname, Oid collnamespace,
 	values[Anum_pg_collation_collprovider - 1] = CharGetDatum(collprovider);
 	values[Anum_pg_collation_collisdeterministic - 1] = BoolGetDatum(collisdeterministic);
 	values[Anum_pg_collation_collencoding - 1] = Int32GetDatum(collencoding);
-	namestrcpy(&name_collate, collcollate);
-	values[Anum_pg_collation_collcollate - 1] = NameGetDatum(&name_collate);
-	namestrcpy(&name_ctype, collctype);
-	values[Anum_pg_collation_collctype - 1] = NameGetDatum(&name_ctype);
+	if (collcollate)
+		values[Anum_pg_collation_collcollate - 1] = CStringGetTextDatum(collcollate);
+	else
+		nulls[Anum_pg_collation_collcollate - 1] = true;
+	if (collctype)
+		values[Anum_pg_collation_collctype - 1] = CStringGetTextDatum(collctype);
+	else
+		nulls[Anum_pg_collation_collctype - 1] = true;
+	if (collicucoll)
+		values[Anum_pg_collation_collicucoll - 1] = CStringGetTextDatum(collicucoll);
+	else
+		nulls[Anum_pg_collation_collicucoll - 1] = true;
 	if (collversion)
 		values[Anum_pg_collation_collversion - 1] = CStringGetTextDatum(collversion);
 	else
diff --git a/src/backend/commands/collationcmds.c b/src/backend/commands/collationcmds.c
index 53fc579f37..7dd125705b 100644
--- a/src/backend/commands/collationcmds.c
+++ b/src/backend/commands/collationcmds.c
@@ -65,6 +65,7 @@ DefineCollation(ParseState *pstate, List *names, List *parameters, bool if_not_e
 	DefElem    *versionEl = NULL;
 	char	   *collcollate = NULL;
 	char	   *collctype = NULL;
+	char	   *collicucoll = NULL;
 	char	   *collproviderstr = NULL;
 	bool		collisdeterministic = true;
 	int			collencoding = 0;
@@ -129,18 +130,36 @@ DefineCollation(ParseState *pstate, List *names, List *parameters, bool if_not_e
 	{
 		Oid			collid;
 		HeapTuple	tp;
+		Datum		datum;
+		bool		isnull;
 
 		collid = get_collation_oid(defGetQualifiedName(fromEl), false);
 		tp = SearchSysCache1(COLLOID, ObjectIdGetDatum(collid));
 		if (!HeapTupleIsValid(tp))
 			elog(ERROR, "cache lookup failed for collation %u", collid);
 
-		collcollate = pstrdup(NameStr(((Form_pg_collation) GETSTRUCT(tp))->collcollate));
-		collctype = pstrdup(NameStr(((Form_pg_collation) GETSTRUCT(tp))->collctype));
 		collprovider = ((Form_pg_collation) GETSTRUCT(tp))->collprovider;
 		collisdeterministic = ((Form_pg_collation) GETSTRUCT(tp))->collisdeterministic;
 		collencoding = ((Form_pg_collation) GETSTRUCT(tp))->collencoding;
 
+		datum = SysCacheGetAttr(COLLOID, tp, Anum_pg_collation_collcollate, &isnull);
+		if (!isnull)
+			collcollate = TextDatumGetCString(datum);
+		else
+			collcollate = NULL;
+
+		datum = SysCacheGetAttr(COLLOID, tp, Anum_pg_collation_collctype, &isnull);
+		if (!isnull)
+			collctype = TextDatumGetCString(datum);
+		else
+			collctype = NULL;
+
+		datum = SysCacheGetAttr(COLLOID, tp, Anum_pg_collation_collicucoll, &isnull);
+		if (!isnull)
+			collicucoll = TextDatumGetCString(datum);
+		else
+			collicucoll = NULL;
+
 		ReleaseSysCache(tp);
 
 		/*
@@ -156,18 +175,6 @@ DefineCollation(ParseState *pstate, List *names, List *parameters, bool if_not_e
 					 errmsg("collation \"default\" cannot be copied")));
 	}
 
-	if (localeEl)
-	{
-		collcollate = defGetString(localeEl);
-		collctype = defGetString(localeEl);
-	}
-
-	if (lccollateEl)
-		collcollate = defGetString(lccollateEl);
-
-	if (lcctypeEl)
-		collctype = defGetString(lcctypeEl);
-
 	if (providerEl)
 		collproviderstr = defGetString(providerEl);
 
@@ -192,15 +199,43 @@ DefineCollation(ParseState *pstate, List *names, List *parameters, bool if_not_e
 	else if (!fromEl)
 		collprovider = COLLPROVIDER_LIBC;
 
-	if (!collcollate)
-		ereport(ERROR,
-				(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
-				 errmsg("parameter \"lc_collate\" must be specified")));
+	if (localeEl)
+	{
+		if (collprovider == COLLPROVIDER_LIBC)
+		{
+			collcollate = defGetString(localeEl);
+			collctype = defGetString(localeEl);
+		}
+		else
+			collicucoll = defGetString(localeEl);
+	}
 
-	if (!collctype)
-		ereport(ERROR,
-				(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
-				 errmsg("parameter \"lc_ctype\" must be specified")));
+	if (lccollateEl)
+		collcollate = defGetString(lccollateEl);
+
+	if (lcctypeEl)
+		collctype = defGetString(lcctypeEl);
+
+	if (collprovider == COLLPROVIDER_LIBC)
+	{
+		if (!collcollate)
+			ereport(ERROR,
+					(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
+					 errmsg("parameter \"lc_collate\" must be specified")));
+
+		if (!collctype)
+			ereport(ERROR,
+					(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
+					 errmsg("parameter \"lc_ctype\" must be specified")));
+	}
+
+	if (collprovider == COLLPROVIDER_ICU)
+	{
+		if (!collicucoll)
+			ereport(ERROR,
+					(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
+					 errmsg("parameter \"locale\" must be specified")));
+	}
 
 	/*
 	 * Nondeterministic collations are currently only supported with ICU
@@ -243,7 +278,7 @@ DefineCollation(ParseState *pstate, List *names, List *parameters, bool if_not_e
 	}
 
 	if (!collversion)
-		collversion = get_collation_actual_version(collprovider, collcollate);
+		collversion = get_collation_actual_version(collprovider, collprovider == COLLPROVIDER_ICU ? collicucoll : collcollate);
 
 	newoid = CollationCreate(collName,
 							 collNamespace,
@@ -253,6 +288,7 @@ DefineCollation(ParseState *pstate, List *names, List *parameters, bool if_not_e
 							 collencoding,
 							 collcollate,
 							 collctype,
+							 collicucoll,
 							 collversion,
 							 if_not_exists,
 							 false);	/* not quiet */
@@ -336,7 +372,13 @@ AlterCollation(AlterCollationStmt *stmt)
 								  &isnull);
 	oldversion = isnull ? NULL : TextDatumGetCString(collversion);
 
-	newversion = get_collation_actual_version(collForm->collprovider, NameStr(collForm->collcollate));
+	{
+		Datum	datum;
+
+		datum = SysCacheGetAttr(COLLOID, tup, collForm->collprovider == COLLPROVIDER_ICU ? Anum_pg_collation_collicucoll : Anum_pg_collation_collcollate, &isnull);
+		Assert(!isnull);
+		newversion = get_collation_actual_version(collForm->collprovider, TextDatumGetCString(datum));
+	}
 
 	/* cannot change from NULL to non-NULL or vice versa */
 	if ((!oldversion && newversion) || (oldversion && !newversion))
@@ -383,8 +425,9 @@ pg_collation_actual_version(PG_FUNCTION_ARGS)
 {
 	Oid			collid = PG_GETARG_OID(0);
 	HeapTuple	tp;
-	char	   *collcollate;
 	char		collprovider;
+	Datum		datum;
+	bool		isnull;
 	char	   *version;
 
 	tp = SearchSysCache1(COLLOID, ObjectIdGetDatum(collid));
@@ -393,12 +436,19 @@ pg_collation_actual_version(PG_FUNCTION_ARGS)
 				(errcode(ERRCODE_UNDEFINED_OBJECT),
 				 errmsg("collation with OID %u does not exist", collid)));
 
-	collcollate = pstrdup(NameStr(((Form_pg_collation) GETSTRUCT(tp))->collcollate));
 	collprovider = ((Form_pg_collation) GETSTRUCT(tp))->collprovider;
 
-	ReleaseSysCache(tp);
+	if (collprovider != COLLPROVIDER_DEFAULT)
+	{
+		datum = SysCacheGetAttr(COLLOID, tp, collprovider == COLLPROVIDER_ICU ? Anum_pg_collation_collicucoll : Anum_pg_collation_collcollate, &isnull);
+		Assert(!isnull);
+
+		version = get_collation_actual_version(collprovider, TextDatumGetCString(datum));
+	}
+	else
+		version = NULL;
 
-	version = get_collation_actual_version(collprovider, collcollate);
+	ReleaseSysCache(tp);
 
 	if (version)
 		PG_RETURN_TEXT_P(cstring_to_text(version));
@@ -623,7 +673,7 @@ pg_import_system_collations(PG_FUNCTION_ARGS)
 			 */
 			collid = CollationCreate(localebuf, nspid, GetUserId(),
 									 COLLPROVIDER_LIBC, true, enc,
-									 localebuf, localebuf,
+									 localebuf, localebuf, NULL,
 									 get_collation_actual_version(COLLPROVIDER_LIBC, localebuf),
 									 true, true);
 			if (OidIsValid(collid))
@@ -684,7 +734,7 @@ pg_import_system_collations(PG_FUNCTION_ARGS)
 
 			collid = CollationCreate(alias, nspid, GetUserId(),
 									 COLLPROVIDER_LIBC, true, enc,
-									 locale, locale,
+									 locale, locale, NULL,
 									 get_collation_actual_version(COLLPROVIDER_LIBC, locale),
 									 true, true);
 			if (OidIsValid(collid))
@@ -725,7 +775,7 @@ pg_import_system_collations(PG_FUNCTION_ARGS)
 			const char *name;
 			char	   *langtag;
 			char	   *icucomment;
-			const char *collcollate;
+			const char *icucollstr;
 			Oid			collid;
 
 			if (i == -1)
@@ -734,20 +784,20 @@ pg_import_system_collations(PG_FUNCTION_ARGS)
 				name = uloc_getAvailable(i);
 
 			langtag = get_icu_language_tag(name);
-			collcollate = U_ICU_VERSION_MAJOR_NUM >= 54 ? langtag : name;
+			icucollstr = U_ICU_VERSION_MAJOR_NUM >= 54 ? langtag : name;
 
 			/*
 			 * Be paranoid about not allowing any non-ASCII strings into
 			 * pg_collation
 			 */
-			if (!pg_is_ascii(langtag) || !pg_is_ascii(collcollate))
+			if (!pg_is_ascii(langtag) || !pg_is_ascii(icucollstr))
 				continue;
 
 			collid = CollationCreate(psprintf("%s-x-icu", langtag),
 									 nspid, GetUserId(),
 									 COLLPROVIDER_ICU, true, -1,
-									 collcollate, collcollate,
-									 get_collation_actual_version(COLLPROVIDER_ICU, collcollate),
+									 NULL, NULL, icucollstr,
+									 get_collation_actual_version(COLLPROVIDER_ICU, icucollstr),
 									 true, true);
 			if (OidIsValid(collid))
 			{
diff --git a/src/backend/commands/dbcommands.c b/src/backend/commands/dbcommands.c
index 029fab48df..7928790cc9 100644
--- a/src/backend/commands/dbcommands.c
+++ b/src/backend/commands/dbcommands.c
@@ -36,6 +36,7 @@
 #include "catalog/indexing.h"
 #include "catalog/objectaccess.h"
 #include "catalog/pg_authid.h"
+#include "catalog/pg_collation.h"
 #include "catalog/pg_database.h"
 #include "catalog/pg_db_role_setting.h"
 #include "catalog/pg_subscription.h"
@@ -86,7 +87,8 @@ static bool get_db_info(const char *name, LOCKMODE lockmode,
 						int *encodingP, bool *dbIsTemplateP, bool *dbAllowConnP,
 						Oid *dbLastSysOidP, TransactionId *dbFrozenXidP,
 						MultiXactId *dbMinMultiP,
-						Oid *dbTablespace, char **dbCollate, char **dbCtype);
+						Oid *dbTablespace, char **dbCollate, char **dbCtype, char **dbIcucoll,
+						char *dbCollProvider);
 static bool have_createdb_privilege(void);
 static void remove_dbtablespaces(Oid db_id);
 static bool check_db_file_conflict(Oid db_id);
@@ -106,6 +108,8 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 	int			src_encoding = -1;
 	char	   *src_collate = NULL;
 	char	   *src_ctype = NULL;
+	char	   *src_icucoll = NULL;
+	char		src_collprovider;
 	bool		src_istemplate;
 	bool		src_allowconn;
 	Oid			src_lastsysoid = InvalidOid;
@@ -127,6 +131,7 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 	DefElem    *dlocale = NULL;
 	DefElem    *dcollate = NULL;
 	DefElem    *dctype = NULL;
+	DefElem	   *dcollprovider = NULL;
 	DefElem    *distemplate = NULL;
 	DefElem    *dallowconnections = NULL;
 	DefElem    *dconnlimit = NULL;
@@ -135,6 +140,8 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 	const char *dbtemplate = NULL;
 	char	   *dbcollate = NULL;
 	char	   *dbctype = NULL;
+	char	   *dbicucoll = NULL;
+	char		dbcollprovider = '\0';
 	char	   *canonname;
 	int			encoding = -1;
 	bool		dbistemplate = false;
@@ -191,6 +198,15 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 				errorConflictingDefElem(defel, pstate);
 			dctype = defel;
 		}
+		else if (strcmp(defel->defname, "collation_provider") == 0)
+		{
+			if (dcollprovider)
+				ereport(ERROR,
+						(errcode(ERRCODE_SYNTAX_ERROR),
+						 errmsg("conflicting or redundant options"),
+						 parser_errposition(pstate, defel->location)));
+			dcollprovider = defel;
+		}
 		else if (strcmp(defel->defname, "is_template") == 0)
 		{
 			if (distemplate)
@@ -224,12 +240,6 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 					 parser_errposition(pstate, defel->location)));
 	}
 
-	if (dlocale && (dcollate || dctype))
-		ereport(ERROR,
-				(errcode(ERRCODE_SYNTAX_ERROR),
-				 errmsg("conflicting or redundant options"),
-				 errdetail("LOCALE cannot be specified together with LC_COLLATE or LC_CTYPE.")));
-
 	if (downer && downer->arg)
 		dbowner = defGetString(downer);
 	if (dtemplate && dtemplate->arg)
@@ -266,11 +276,29 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 	{
 		dbcollate = defGetString(dlocale);
 		dbctype = defGetString(dlocale);
+		dbicucoll = defGetString(dlocale);
 	}
 	if (dcollate && dcollate->arg)
 		dbcollate = defGetString(dcollate);
 	if (dctype && dctype->arg)
 		dbctype = defGetString(dctype);
+	if (dcollprovider && dcollprovider->arg)
+	{
+		char	   *collproviderstr = defGetString(dcollprovider);
+
+#ifdef USE_ICU
+		if (pg_strcasecmp(collproviderstr, "icu") == 0)
+			dbcollprovider = COLLPROVIDER_ICU;
+		else
+#endif
+		if (pg_strcasecmp(collproviderstr, "libc") == 0)
+			dbcollprovider = COLLPROVIDER_LIBC;
+		else
+			ereport(ERROR,
+					(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
+					 errmsg("unrecognized collation provider: %s",
+							collproviderstr)));
+	}
 	if (distemplate && distemplate->arg)
 		dbistemplate = defGetBoolean(distemplate);
 	if (dallowconnections && dallowconnections->arg)
@@ -320,7 +348,7 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 					 &src_dboid, &src_owner, &src_encoding,
 					 &src_istemplate, &src_allowconn, &src_lastsysoid,
 					 &src_frozenxid, &src_minmxid, &src_deftablespace,
-					 &src_collate, &src_ctype))
+					 &src_collate, &src_ctype, &src_icucoll, &src_collprovider))
 		ereport(ERROR,
 				(errcode(ERRCODE_UNDEFINED_DATABASE),
 				 errmsg("template database \"%s\" does not exist",
@@ -346,6 +374,10 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 		dbcollate = src_collate;
 	if (dbctype == NULL)
 		dbctype = src_ctype;
+	if (dbicucoll == NULL)
+		dbicucoll = src_icucoll;
+	if (dbcollprovider == '\0')
+		dbcollprovider = src_collprovider;
 
 	/* Some encodings are client only */
 	if (!PG_VALID_BE_ENCODING(encoding))
@@ -525,10 +557,13 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 		DirectFunctionCall1(namein, CStringGetDatum(dbname));
 	new_record[Anum_pg_database_datdba - 1] = ObjectIdGetDatum(datdba);
 	new_record[Anum_pg_database_encoding - 1] = Int32GetDatum(encoding);
-	new_record[Anum_pg_database_datcollate - 1] =
-		DirectFunctionCall1(namein, CStringGetDatum(dbcollate));
-	new_record[Anum_pg_database_datctype - 1] =
-		DirectFunctionCall1(namein, CStringGetDatum(dbctype));
+	new_record[Anum_pg_database_datcollate - 1] = CStringGetTextDatum(dbcollate);
+	new_record[Anum_pg_database_datctype - 1] = CStringGetTextDatum(dbctype);
+	if (dbicucoll)
+		new_record[Anum_pg_database_daticucoll - 1] = CStringGetTextDatum(dbicucoll);
+	else
+		new_record_nulls[Anum_pg_database_daticucoll] = true;
+	new_record[Anum_pg_database_datcollprovider - 1] = CharGetDatum(dbcollprovider);
 	new_record[Anum_pg_database_datistemplate - 1] = BoolGetDatum(dbistemplate);
 	new_record[Anum_pg_database_datallowconn - 1] = BoolGetDatum(dballowconnections);
 	new_record[Anum_pg_database_datconnlimit - 1] = Int32GetDatum(dbconnlimit);
@@ -802,7 +837,7 @@ dropdb(const char *dbname, bool missing_ok, bool force)
 	pgdbrel = table_open(DatabaseRelationId, RowExclusiveLock);
 
 	if (!get_db_info(dbname, AccessExclusiveLock, &db_id, NULL, NULL,
-					 &db_istemplate, NULL, NULL, NULL, NULL, NULL, NULL, NULL))
+					 &db_istemplate, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL))
 	{
 		if (!missing_ok)
 		{
@@ -1001,7 +1036,7 @@ RenameDatabase(const char *oldname, const char *newname)
 	rel = table_open(DatabaseRelationId, RowExclusiveLock);
 
 	if (!get_db_info(oldname, AccessExclusiveLock, &db_id, NULL, NULL,
-					 NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL))
+					 NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL))
 		ereport(ERROR,
 				(errcode(ERRCODE_UNDEFINED_DATABASE),
 				 errmsg("database \"%s\" does not exist", oldname)));
@@ -1114,7 +1149,7 @@ movedb(const char *dbname, const char *tblspcname)
 	pgdbrel = table_open(DatabaseRelationId, RowExclusiveLock);
 
 	if (!get_db_info(dbname, AccessExclusiveLock, &db_id, NULL, NULL,
-					 NULL, NULL, NULL, NULL, NULL, &src_tblspcoid, NULL, NULL))
+					 NULL, NULL, NULL, NULL, NULL, &src_tblspcoid, NULL, NULL, NULL, NULL))
 		ereport(ERROR,
 				(errcode(ERRCODE_UNDEFINED_DATABASE),
 				 errmsg("database \"%s\" does not exist", dbname)));
@@ -1759,7 +1794,8 @@ get_db_info(const char *name, LOCKMODE lockmode,
 			int *encodingP, bool *dbIsTemplateP, bool *dbAllowConnP,
 			Oid *dbLastSysOidP, TransactionId *dbFrozenXidP,
 			MultiXactId *dbMinMultiP,
-			Oid *dbTablespace, char **dbCollate, char **dbCtype)
+			Oid *dbTablespace, char **dbCollate, char **dbCtype, char **dbIcucoll,
+			char *dbCollProvider)
 {
 	bool		result = false;
 	Relation	relation;
@@ -1824,6 +1860,9 @@ get_db_info(const char *name, LOCKMODE lockmode,
 
 			if (strcmp(name, NameStr(dbform->datname)) == 0)
 			{
+				Datum		datum;
+				bool		isnull;
+
 				/* oid of the database */
 				if (dbIdP)
 					*dbIdP = dbOid;
@@ -1852,10 +1891,28 @@ get_db_info(const char *name, LOCKMODE lockmode,
 				if (dbTablespace)
 					*dbTablespace = dbform->dattablespace;
 				/* default locale settings for this database */
+				if (dbCollProvider)
+					*dbCollProvider = dbform->datcollprovider;
 				if (dbCollate)
-					*dbCollate = pstrdup(NameStr(dbform->datcollate));
+				{
+					datum = SysCacheGetAttr(DATABASEOID, tuple, Anum_pg_database_datcollate, &isnull);
+					Assert(!isnull);
+					*dbCollate = TextDatumGetCString(datum);
+				}
 				if (dbCtype)
-					*dbCtype = pstrdup(NameStr(dbform->datctype));
+				{
+					datum = SysCacheGetAttr(DATABASEOID, tuple, Anum_pg_database_datctype, &isnull);
+					Assert(!isnull);
+					*dbCtype = TextDatumGetCString(datum);
+				}
+				if (dbIcucoll)
+				{
+					datum = SysCacheGetAttr(DATABASEOID, tuple, Anum_pg_database_daticucoll, &isnull);
+					if (isnull)
+						*dbIcucoll = NULL;
+					else
+						*dbIcucoll = TextDatumGetCString(datum);
+				}
 				ReleaseSysCache(tuple);
 				result = true;
 				break;
diff --git a/src/backend/regex/regc_pg_locale.c b/src/backend/regex/regc_pg_locale.c
index bbbd61c604..3fe0f1c386 100644
--- a/src/backend/regex/regc_pg_locale.c
+++ b/src/backend/regex/regc_pg_locale.c
@@ -241,7 +241,12 @@ pg_set_regex_collation(Oid collation)
 	else
 	{
 		if (collation == DEFAULT_COLLATION_OID)
-			pg_regex_locale = 0;
+		{
+			if (default_locale.provider == COLLPROVIDER_ICU)
+				pg_regex_locale = &default_locale;
+			else
+				pg_regex_locale = 0;
+		}
 		else if (OidIsValid(collation))
 		{
 			/*
diff --git a/src/backend/utils/adt/formatting.c b/src/backend/utils/adt/formatting.c
index 419469fab5..320047fbd0 100644
--- a/src/backend/utils/adt/formatting.c
+++ b/src/backend/utils/adt/formatting.c
@@ -1666,6 +1666,8 @@ str_tolower(const char *buff, size_t nbytes, Oid collid)
 			}
 			mylocale = pg_newlocale_from_collation(collid);
 		}
+		else if (default_locale.provider == COLLPROVIDER_ICU)
+			mylocale = &default_locale;
 
 #ifdef USE_ICU
 		if (mylocale && mylocale->provider == COLLPROVIDER_ICU)
@@ -1790,6 +1792,8 @@ str_toupper(const char *buff, size_t nbytes, Oid collid)
 			}
 			mylocale = pg_newlocale_from_collation(collid);
 		}
+		else if (default_locale.provider == COLLPROVIDER_ICU)
+			mylocale = &default_locale;
 
 #ifdef USE_ICU
 		if (mylocale && mylocale->provider == COLLPROVIDER_ICU)
@@ -1915,6 +1919,8 @@ str_initcap(const char *buff, size_t nbytes, Oid collid)
 			}
 			mylocale = pg_newlocale_from_collation(collid);
 		}
+		else if (default_locale.provider == COLLPROVIDER_ICU)
+			mylocale = &default_locale;
 
 #ifdef USE_ICU
 		if (mylocale && mylocale->provider == COLLPROVIDER_ICU)
diff --git a/src/backend/utils/adt/like.c b/src/backend/utils/adt/like.c
index eed183cd0d..85a668fa36 100644
--- a/src/backend/utils/adt/like.c
+++ b/src/backend/utils/adt/like.c
@@ -150,9 +150,14 @@ SB_lower_char(unsigned char c, pg_locale_t locale, bool locale_is_c)
 static inline int
 GenericMatchText(const char *s, int slen, const char *p, int plen, Oid collation)
 {
-	if (collation && !lc_ctype_is_c(collation) && collation != DEFAULT_COLLATION_OID)
+	if (collation && !lc_ctype_is_c(collation))
 	{
-		pg_locale_t locale = pg_newlocale_from_collation(collation);
+		pg_locale_t locale = 0;
+
+		if (collation != DEFAULT_COLLATION_OID)
+			locale = pg_newlocale_from_collation(collation);
+		else if (default_locale.provider == COLLPROVIDER_ICU)
+			locale = &default_locale;
 
 		if (locale && !locale->deterministic)
 			ereport(ERROR,
@@ -195,11 +200,14 @@ Generic_Text_IC_like(text *str, text *pat, Oid collation)
 		}
 		locale = pg_newlocale_from_collation(collation);
 
-		if (locale && !locale->deterministic)
-			ereport(ERROR,
-					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-					 errmsg("nondeterministic collations are not supported for ILIKE")));
 	}
+	else if (default_locale.provider == COLLPROVIDER_ICU)
+		locale = &default_locale;
+
+	if (locale && !locale->deterministic)
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				 errmsg("nondeterministic collations are not supported for ILIKE")));
 
 	/*
 	 * For efficiency reasons, in the single byte case we don't call lower()
diff --git a/src/backend/utils/adt/like_support.c b/src/backend/utils/adt/like_support.c
index 988568825e..6b82ad1d43 100644
--- a/src/backend/utils/adt/like_support.c
+++ b/src/backend/utils/adt/like_support.c
@@ -1030,6 +1030,8 @@ like_fixed_prefix(Const *patt_const, bool case_insensitive, Oid collation,
 			}
 			locale = pg_newlocale_from_collation(collation);
 		}
+		else if (default_locale.provider == COLLPROVIDER_ICU)
+			locale = &default_locale;
 	}
 
 	if (typeid != BYTEAOID)
diff --git a/src/backend/utils/adt/pg_locale.c b/src/backend/utils/adt/pg_locale.c
index cc2ab95535..8d32bc68d8 100644
--- a/src/backend/utils/adt/pg_locale.c
+++ b/src/backend/utils/adt/pg_locale.c
@@ -1289,21 +1289,36 @@ lookup_collation_cache(Oid collation, bool set_flags)
 		/* Attempt to set the flags */
 		HeapTuple	tp;
 		Form_pg_collation collform;
-		const char *collcollate;
-		const char *collctype;
 
 		tp = SearchSysCache1(COLLOID, ObjectIdGetDatum(collation));
 		if (!HeapTupleIsValid(tp))
 			elog(ERROR, "cache lookup failed for collation %u", collation);
 		collform = (Form_pg_collation) GETSTRUCT(tp);
 
-		collcollate = NameStr(collform->collcollate);
-		collctype = NameStr(collform->collctype);
-
-		cache_entry->collate_is_c = ((strcmp(collcollate, "C") == 0) ||
-									 (strcmp(collcollate, "POSIX") == 0));
-		cache_entry->ctype_is_c = ((strcmp(collctype, "C") == 0) ||
-								   (strcmp(collctype, "POSIX") == 0));
+		if (collform->collprovider == COLLPROVIDER_LIBC)
+		{
+			Datum		datum;
+			bool		isnull;
+			const char *collcollate;
+			const char *collctype;
+
+			datum = SysCacheGetAttr(COLLOID, tp, Anum_pg_collation_collcollate, &isnull);
+			Assert(!isnull);
+			collcollate = TextDatumGetCString(datum);
+			datum = SysCacheGetAttr(COLLOID, tp, Anum_pg_collation_collctype, &isnull);
+			Assert(!isnull);
+			collctype = TextDatumGetCString(datum);
+
+			cache_entry->collate_is_c = ((strcmp(collcollate, "C") == 0) ||
+										 (strcmp(collcollate, "POSIX") == 0));
+			cache_entry->ctype_is_c = ((strcmp(collctype, "C") == 0) ||
+									   (strcmp(collctype, "POSIX") == 0));
+		}
+		else
+		{
+			cache_entry->collate_is_c = false;
+			cache_entry->ctype_is_c = false;
+		}
 
 		cache_entry->flags_valid = true;
 
@@ -1336,6 +1351,9 @@ lc_collate_is_c(Oid collation)
 		static int	result = -1;
 		char	   *localeptr;
 
+		if (default_locale.provider == COLLPROVIDER_ICU)
+			return false;
+
 		if (result >= 0)
 			return (bool) result;
 		localeptr = setlocale(LC_COLLATE, NULL);
@@ -1386,6 +1404,9 @@ lc_ctype_is_c(Oid collation)
 		static int	result = -1;
 		char	   *localeptr;
 
+		if (default_locale.provider == COLLPROVIDER_ICU)
+			return false;
+
 		if (result >= 0)
 			return (bool) result;
 		localeptr = setlocale(LC_CTYPE, NULL);
@@ -1414,6 +1435,88 @@ lc_ctype_is_c(Oid collation)
 	return (lookup_collation_cache(collation, true))->ctype_is_c;
 }
 
+struct pg_locale_struct default_locale;
+
+void
+make_icu_collator(const char *icucollstr,
+				  struct pg_locale_struct *resultp)
+{
+#ifdef USE_ICU
+	UCollator  *collator;
+	UErrorCode	status;
+
+	status = U_ZERO_ERROR;
+	collator = ucol_open(icucollstr, &status);
+	if (U_FAILURE(status))
+		ereport(ERROR,
+				(errmsg("could not open collator for locale \"%s\": %s",
+						icucollstr, u_errorName(status))));
+
+	if (U_ICU_VERSION_MAJOR_NUM < 54)
+		icu_set_collation_attributes(collator, icucollstr);
+
+	/* We will leak this string if we get an error below :-( */
+	resultp->info.icu.locale = MemoryContextStrdup(TopMemoryContext, icucollstr);
+	resultp->info.icu.ucol = collator;
+#else							/* not USE_ICU */
+	/* could get here if a collation was created by a build with ICU */
+	ereport(ERROR,
+			(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+			 errmsg("ICU is not supported in this build"), \
+			 errhint("You need to rebuild PostgreSQL using %s.", "--with-icu")));
+#endif							/* not USE_ICU */
+}
+
+void
+check_collation_version(HeapTuple colltuple)
+{
+	Form_pg_collation collform;
+	Datum		collversion;
+	bool		isnull;
+
+	collform = (Form_pg_collation) GETSTRUCT(colltuple);
+
+	collversion = SysCacheGetAttr(COLLOID, colltuple, Anum_pg_collation_collversion,
+								  &isnull);
+	if (!isnull)
+	{
+		char	   *actual_versionstr;
+		char	   *collversionstr;
+		Datum		datum;
+		bool		isnull;
+
+		datum = SysCacheGetAttr(COLLOID, colltuple, collform->collprovider == COLLPROVIDER_ICU ? Anum_pg_collation_collicucoll : Anum_pg_collation_collcollate, &isnull);
+		Assert(!isnull);
+
+		actual_versionstr = get_collation_actual_version(collform->collprovider,
+														 TextDatumGetCString(datum));
+		if (!actual_versionstr)
+		{
+			/*
+			 * This could happen when specifying a version in CREATE
+			 * COLLATION for a libc locale, or manually creating a mess in
+			 * the catalogs.
+			 */
+			ereport(ERROR,
+					(errmsg("collation \"%s\" has no actual version, but a version was specified",
+							NameStr(collform->collname))));
+		}
+		collversionstr = TextDatumGetCString(collversion);
+
+		if (strcmp(actual_versionstr, collversionstr) != 0)
+			ereport(WARNING,
+					(errmsg("collation \"%s\" has version mismatch",
+							NameStr(collform->collname)),
+					 errdetail("The collation in the database was created using version %s, "
+							   "but the operating system provides version %s.",
+							   collversionstr, actual_versionstr),
+					 errhint("Rebuild all objects affected by this collation and run "
+							 "ALTER COLLATION %s REFRESH VERSION, "
+							 "or build PostgreSQL with the right library version.",
+							 quote_qualified_identifier(get_namespace_name(collform->collnamespace),
+														NameStr(collform->collname)))));
+	}
+}
 
 /* simple subroutine for reporting errors from newlocale() */
 #ifdef HAVE_LOCALE_T
@@ -1483,21 +1586,14 @@ pg_newlocale_from_collation(Oid collid)
 		/* We haven't computed this yet in this session, so do it */
 		HeapTuple	tp;
 		Form_pg_collation collform;
-		const char *collcollate;
-		const char *collctype pg_attribute_unused();
 		struct pg_locale_struct result;
 		pg_locale_t resultp;
-		Datum		collversion;
-		bool		isnull;
 
 		tp = SearchSysCache1(COLLOID, ObjectIdGetDatum(collid));
 		if (!HeapTupleIsValid(tp))
 			elog(ERROR, "cache lookup failed for collation %u", collid);
 		collform = (Form_pg_collation) GETSTRUCT(tp);
 
-		collcollate = NameStr(collform->collcollate);
-		collctype = NameStr(collform->collctype);
-
 		/* We'll fill in the result struct locally before allocating memory */
 		memset(&result, 0, sizeof(result));
 		result.provider = collform->collprovider;
@@ -1506,8 +1602,19 @@ pg_newlocale_from_collation(Oid collid)
 		if (collform->collprovider == COLLPROVIDER_LIBC)
 		{
 #ifdef HAVE_LOCALE_T
+			Datum		datum;
+			bool		isnull;
+			const char *collcollate;
+			const char *collctype pg_attribute_unused();
 			locale_t	loc;
 
+			datum = SysCacheGetAttr(COLLOID, tp, Anum_pg_collation_collcollate, &isnull);
+			Assert(!isnull);
+			collcollate = TextDatumGetCString(datum);
+			datum = SysCacheGetAttr(COLLOID, tp, Anum_pg_collation_collctype, &isnull);
+			Assert(!isnull);
+			collctype = TextDatumGetCString(datum);
+
 			if (strcmp(collcollate, collctype) == 0)
 			{
 				/* Normal case where they're the same */
@@ -1558,72 +1665,17 @@ pg_newlocale_from_collation(Oid collid)
 		}
 		else if (collform->collprovider == COLLPROVIDER_ICU)
 		{
-#ifdef USE_ICU
-			UCollator  *collator;
-			UErrorCode	status;
-
-			if (strcmp(collcollate, collctype) != 0)
-				ereport(ERROR,
-						(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-						 errmsg("collations with different collate and ctype values are not supported by ICU")));
-
-			status = U_ZERO_ERROR;
-			collator = ucol_open(collcollate, &status);
-			if (U_FAILURE(status))
-				ereport(ERROR,
-						(errmsg("could not open collator for locale \"%s\": %s",
-								collcollate, u_errorName(status))));
-
-			if (U_ICU_VERSION_MAJOR_NUM < 54)
-				icu_set_collation_attributes(collator, collcollate);
-
-			/* We will leak this string if we get an error below :-( */
-			result.info.icu.locale = MemoryContextStrdup(TopMemoryContext,
-														 collcollate);
-			result.info.icu.ucol = collator;
-#else							/* not USE_ICU */
-			/* could get here if a collation was created by a build with ICU */
-			ereport(ERROR,
-					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-					 errmsg("ICU is not supported in this build"), \
-					 errhint("You need to rebuild PostgreSQL using %s.", "--with-icu")));
-#endif							/* not USE_ICU */
+			Datum		datum;
+			bool		isnull;
+			const char *icucollstr;;
+
+			datum = SysCacheGetAttr(COLLOID, tp, Anum_pg_collation_collicucoll, &isnull);
+			Assert(!isnull);
+			icucollstr = TextDatumGetCString(datum);
+			make_icu_collator(icucollstr, &result);
 		}
 
-		collversion = SysCacheGetAttr(COLLOID, tp, Anum_pg_collation_collversion,
-									  &isnull);
-		if (!isnull)
-		{
-			char	   *actual_versionstr;
-			char	   *collversionstr;
-
-			actual_versionstr = get_collation_actual_version(collform->collprovider, collcollate);
-			if (!actual_versionstr)
-			{
-				/*
-				 * This could happen when specifying a version in CREATE
-				 * COLLATION for a libc locale, or manually creating a mess in
-				 * the catalogs.
-				 */
-				ereport(ERROR,
-						(errmsg("collation \"%s\" has no actual version, but a version was specified",
-								NameStr(collform->collname))));
-			}
-			collversionstr = TextDatumGetCString(collversion);
-
-			if (strcmp(actual_versionstr, collversionstr) != 0)
-				ereport(WARNING,
-						(errmsg("collation \"%s\" has version mismatch",
-								NameStr(collform->collname)),
-						 errdetail("The collation in the database was created using version %s, "
-								   "but the operating system provides version %s.",
-								   collversionstr, actual_versionstr),
-						 errhint("Rebuild all objects affected by this collation and run "
-								 "ALTER COLLATION %s REFRESH VERSION, "
-								 "or build PostgreSQL with the right library version.",
-								 quote_qualified_identifier(get_namespace_name(collform->collnamespace),
-															NameStr(collform->collname)))));
-		}
+		check_collation_version(tp);
 
 		ReleaseSysCache(tp);
 
@@ -1646,6 +1698,17 @@ get_collation_actual_version(char collprovider, const char *collcollate)
 {
 	char	   *collversion = NULL;
 
+	if (collprovider == COLLPROVIDER_DEFAULT)
+	{
+#ifdef USE_ICU
+		if (default_locale.provider == COLLPROVIDER_ICU)
+			collversion = get_collation_actual_version(default_locale.provider,
+													   default_locale.info.icu.locale);
+		else
+#endif
+			collversion = NULL;
+	}
+	else
 #ifdef USE_ICU
 	if (collprovider == COLLPROVIDER_ICU)
 	{
diff --git a/src/backend/utils/adt/varchar.c b/src/backend/utils/adt/varchar.c
index 8fc84649f1..7eb9e59a2c 100644
--- a/src/backend/utils/adt/varchar.c
+++ b/src/backend/utils/adt/varchar.c
@@ -750,7 +750,7 @@ bpchareq(PG_FUNCTION_ARGS)
 	len2 = bcTruelen(arg2);
 
 	if (lc_collate_is_c(collid) ||
-		collid == DEFAULT_COLLATION_OID ||
+		(collid == DEFAULT_COLLATION_OID && default_locale.deterministic) ||
 		pg_newlocale_from_collation(collid)->deterministic)
 	{
 		/*
@@ -790,7 +790,7 @@ bpcharne(PG_FUNCTION_ARGS)
 	len2 = bcTruelen(arg2);
 
 	if (lc_collate_is_c(collid) ||
-		collid == DEFAULT_COLLATION_OID ||
+		(collid == DEFAULT_COLLATION_OID && default_locale.deterministic) ||
 		pg_newlocale_from_collation(collid)->deterministic)
 	{
 		/*
@@ -996,8 +996,13 @@ hashbpchar(PG_FUNCTION_ARGS)
 	keydata = VARDATA_ANY(key);
 	keylen = bcTruelen(key);
 
-	if (!lc_collate_is_c(collid) && collid != DEFAULT_COLLATION_OID)
-		mylocale = pg_newlocale_from_collation(collid);
+	if (!lc_collate_is_c(collid))
+	{
+		if (collid != DEFAULT_COLLATION_OID)
+			mylocale = pg_newlocale_from_collation(collid);
+		else if (default_locale.provider == COLLPROVIDER_ICU)
+			mylocale = &default_locale;
+	}
 
 	if (!mylocale || mylocale->deterministic)
 	{
@@ -1056,8 +1061,13 @@ hashbpcharextended(PG_FUNCTION_ARGS)
 	keydata = VARDATA_ANY(key);
 	keylen = bcTruelen(key);
 
-	if (!lc_collate_is_c(collid) && collid != DEFAULT_COLLATION_OID)
-		mylocale = pg_newlocale_from_collation(collid);
+	if (!lc_collate_is_c(collid))
+	{
+		if (collid != DEFAULT_COLLATION_OID)
+			mylocale = pg_newlocale_from_collation(collid);
+		else if (default_locale.provider == COLLPROVIDER_ICU)
+			mylocale = &default_locale;
+	}
 
 	if (!mylocale || mylocale->deterministic)
 	{
diff --git a/src/backend/utils/adt/varlena.c b/src/backend/utils/adt/varlena.c
index bd3091bbfb..5492c85f36 100644
--- a/src/backend/utils/adt/varlena.c
+++ b/src/backend/utils/adt/varlena.c
@@ -1200,8 +1200,13 @@ text_position_setup(text *t1, text *t2, Oid collid, TextPositionState *state)
 
 	check_collation_set(collid);
 
-	if (!lc_collate_is_c(collid) && collid != DEFAULT_COLLATION_OID)
-		mylocale = pg_newlocale_from_collation(collid);
+	if (!lc_collate_is_c(collid))
+	{
+		if (collid != DEFAULT_COLLATION_OID)
+			mylocale = pg_newlocale_from_collation(collid);
+		else if (default_locale.provider == COLLPROVIDER_ICU)
+			mylocale = &default_locale;
+	}
 
 	if (mylocale && !mylocale->deterministic)
 		ereport(ERROR,
@@ -1560,6 +1565,8 @@ varstr_cmp(const char *arg1, int len1, const char *arg2, int len2, Oid collid)
 
 		if (collid != DEFAULT_COLLATION_OID)
 			mylocale = pg_newlocale_from_collation(collid);
+		else if (default_locale.provider == COLLPROVIDER_ICU)
+			mylocale = &default_locale;
 
 		/*
 		 * memcmp() can't tell us which of two unequal strings sorts first,
@@ -1781,7 +1788,7 @@ texteq(PG_FUNCTION_ARGS)
 	check_collation_set(collid);
 
 	if (lc_collate_is_c(collid) ||
-		collid == DEFAULT_COLLATION_OID ||
+		(collid == DEFAULT_COLLATION_OID && default_locale.deterministic) ||
 		pg_newlocale_from_collation(collid)->deterministic)
 	{
 		Datum		arg1 = PG_GETARG_DATUM(0);
@@ -1835,7 +1842,7 @@ textne(PG_FUNCTION_ARGS)
 	check_collation_set(collid);
 
 	if (lc_collate_is_c(collid) ||
-		collid == DEFAULT_COLLATION_OID ||
+		(collid == DEFAULT_COLLATION_OID && default_locale.deterministic) ||
 		pg_newlocale_from_collation(collid)->deterministic)
 	{
 		Datum		arg1 = PG_GETARG_DATUM(0);
@@ -1947,8 +1954,13 @@ text_starts_with(PG_FUNCTION_ARGS)
 
 	check_collation_set(collid);
 
-	if (!lc_collate_is_c(collid) && collid != DEFAULT_COLLATION_OID)
-		mylocale = pg_newlocale_from_collation(collid);
+	if (!lc_collate_is_c(collid))
+	{
+		if (collid != DEFAULT_COLLATION_OID)
+			mylocale = pg_newlocale_from_collation(collid);
+		else if (default_locale.provider == COLLPROVIDER_ICU)
+			mylocale = &default_locale;
+	}
 
 	if (mylocale && !mylocale->deterministic)
 		ereport(ERROR,
@@ -2063,6 +2075,8 @@ varstr_sortsupport(SortSupport ssup, Oid typid, Oid collid)
 		 */
 		if (collid != DEFAULT_COLLATION_OID)
 			locale = pg_newlocale_from_collation(collid);
+		else if (default_locale.provider == COLLPROVIDER_ICU)
+			locale = &default_locale;
 
 		/*
 		 * There is a further exception on Windows.  When the database
diff --git a/src/backend/utils/init/postinit.c b/src/backend/utils/init/postinit.c
index 7292e51f7d..2319166e91 100644
--- a/src/backend/utils/init/postinit.c
+++ b/src/backend/utils/init/postinit.c
@@ -30,6 +30,7 @@
 #include "catalog/catalog.h"
 #include "catalog/namespace.h"
 #include "catalog/pg_authid.h"
+#include "catalog/pg_collation.h"
 #include "catalog/pg_database.h"
 #include "catalog/pg_db_role_setting.h"
 #include "catalog/pg_tablespace.h"
@@ -53,6 +54,7 @@
 #include "storage/sync.h"
 #include "tcop/tcopprot.h"
 #include "utils/acl.h"
+#include "utils/builtins.h"
 #include "utils/fmgroids.h"
 #include "utils/guc.h"
 #include "utils/memutils.h"
@@ -306,6 +308,8 @@ CheckMyDatabase(const char *name, bool am_superuser, bool override_allow_connect
 {
 	HeapTuple	tup;
 	Form_pg_database dbform;
+	Datum		datum;
+	bool		isnull;
 	char	   *collate;
 	char	   *ctype;
 
@@ -389,8 +393,12 @@ CheckMyDatabase(const char *name, bool am_superuser, bool override_allow_connect
 					PGC_BACKEND, PGC_S_DYNAMIC_DEFAULT);
 
 	/* assign locale variables */
-	collate = NameStr(dbform->datcollate);
-	ctype = NameStr(dbform->datctype);
+	datum = SysCacheGetAttr(DATABASEOID, tup, Anum_pg_database_datcollate, &isnull);
+	Assert(!isnull);
+	collate = TextDatumGetCString(datum);
+	datum = SysCacheGetAttr(DATABASEOID, tup, Anum_pg_database_datctype, &isnull);
+	Assert(!isnull);
+	ctype = TextDatumGetCString(datum);
 
 	if (pg_perm_setlocale(LC_COLLATE, collate) == NULL)
 		ereport(FATAL,
@@ -406,6 +414,31 @@ CheckMyDatabase(const char *name, bool am_superuser, bool override_allow_connect
 						   " which is not recognized by setlocale().", ctype),
 				 errhint("Recreate the database with another locale or install the missing locale.")));
 
+	if (dbform->datcollprovider == COLLPROVIDER_ICU)
+	{
+		datum = SysCacheGetAttr(DATABASEOID, tup, Anum_pg_database_daticucoll, &isnull);
+		Assert(!isnull);
+		make_icu_collator(TextDatumGetCString(datum), &default_locale);
+	}
+
+	default_locale.provider = dbform->datcollprovider;
+	/*
+	 * Default locale is currently always deterministic.  Nondeterministic
+	 * locales currently don't support pattern matching, which would break a
+	 * lot of things if applied globally.
+	 */
+	default_locale.deterministic = true;
+
+	{
+		HeapTuple	tp;
+
+		tp = SearchSysCache1(COLLOID, ObjectIdGetDatum(DEFAULT_COLLATION_OID));
+		if (!HeapTupleIsValid(tp))
+			elog(ERROR, "cache lookup failed for collation %u", DEFAULT_COLLATION_OID);
+		check_collation_version(tp);
+		ReleaseSysCache(tp);
+	}
+
 	/* Make the locale settings visible as GUC variables, too */
 	SetConfigOption("lc_collate", collate, PGC_INTERNAL, PGC_S_OVERRIDE);
 	SetConfigOption("lc_ctype", ctype, PGC_INTERNAL, PGC_S_OVERRIDE);
diff --git a/src/bin/initdb/Makefile b/src/bin/initdb/Makefile
index a620a5bea0..993d2fa7a3 100644
--- a/src/bin/initdb/Makefile
+++ b/src/bin/initdb/Makefile
@@ -62,6 +62,8 @@ clean distclean maintainer-clean:
 # ensure that changes in datadir propagate into object file
 initdb.o: initdb.c $(top_builddir)/src/Makefile.global
 
+export with_icu
+
 check:
 	$(prove_check)
 
diff --git a/src/bin/initdb/initdb.c b/src/bin/initdb/initdb.c
index 03b80f9575..9ee0037d50 100644
--- a/src/bin/initdb/initdb.c
+++ b/src/bin/initdb/initdb.c
@@ -131,6 +131,8 @@ static char *lc_monetary = NULL;
 static char *lc_numeric = NULL;
 static char *lc_time = NULL;
 static char *lc_messages = NULL;
+static char collation_provider[] = {COLLPROVIDER_LIBC, '\0'};
+static char *icu_locale = NULL;
 static const char *default_text_search_config = NULL;
 static char *username = NULL;
 static bool pwprompt = false;
@@ -1404,6 +1406,12 @@ bootstrap_template1(void)
 	bki_lines = replace_token(bki_lines, "LC_CTYPE",
 							  escape_quotes_bki(lc_ctype));
 
+	bki_lines = replace_token(bki_lines, "ICUCOLL",
+							  escape_quotes_bki(collation_provider[0] == COLLPROVIDER_ICU ? icu_locale : "_null_"));
+
+	bki_lines = replace_token(bki_lines, "COLLPROVIDER",
+							  collation_provider);
+
 	/* Also ensure backend isn't confused by this environment var: */
 	unsetenv("PGCLIENTENCODING");
 
@@ -1586,6 +1594,12 @@ setup_description(FILE *cmdfd)
 static void
 setup_collation(FILE *cmdfd)
 {
+	/*
+	 * Set version of the default collation.
+	 */
+	PG_CMD_PRINTF("UPDATE pg_collation SET collversion = pg_collation_actual_version(oid) WHERE oid = %d;\n\n",
+				  DEFAULT_COLLATION_OID);
+
 	/*
 	 * Add an SQL-standard name.  We don't want to pin this, so it doesn't go
 	 * in pg_collation.h.  But add it before reading system collations, so
@@ -1839,8 +1853,6 @@ make_template0(FILE *cmdfd)
 {
 	const char *const *line;
 	static const char *const template0_setup[] = {
-		"CREATE DATABASE template0 IS_TEMPLATE = true ALLOW_CONNECTIONS = false;\n\n",
-
 		/*
 		 * We use the OID of template0 to determine datlastsysoid
 		 */
@@ -1865,6 +1877,9 @@ make_template0(FILE *cmdfd)
 		NULL
 	};
 
+	PG_CMD_PRINTF("CREATE DATABASE template0 IS_TEMPLATE = true ALLOW_CONNECTIONS = false COLLATION_PROVIDER = %s;\n\n",
+				  collation_provider[0] == COLLPROVIDER_ICU ? "icu" : "libc");
+
 	for (line = template0_setup; *line; line++)
 		PG_CMD_PUTS(*line);
 }
@@ -2136,13 +2151,14 @@ setlocales(void)
 			lc_monetary = locale;
 		if (!lc_messages)
 			lc_messages = locale;
+		if (!icu_locale)
+			icu_locale = locale;
 	}
 
 	/*
 	 * canonicalize locale names, and obtain any missing values from our
 	 * current environment
 	 */
-
 	check_locale_name(LC_CTYPE, lc_ctype, &canonname);
 	lc_ctype = canonname;
 	check_locale_name(LC_COLLATE, lc_collate, &canonname);
@@ -2161,6 +2177,18 @@ setlocales(void)
 	check_locale_name(LC_CTYPE, lc_messages, &canonname);
 	lc_messages = canonname;
 #endif
+
+	/*
+	 * If ICU is selected but no ICU locale has been given, take the
+	 * lc_collate locale and chop off any encoding suffix.  This should give
+	 * the user a configuration that resembles their operating system's locale
+	 * setup.
+	 */
+	if (collation_provider[0] == COLLPROVIDER_ICU && !icu_locale)
+	{
+		icu_locale = pg_strdup(lc_collate);
+		icu_locale[strcspn(icu_locale, ".")] = '\0';
+	}
 }
 
 /*
@@ -2176,9 +2204,12 @@ usage(const char *progname)
 	printf(_("  -A, --auth=METHOD         default authentication method for local connections\n"));
 	printf(_("      --auth-host=METHOD    default authentication method for local TCP/IP connections\n"));
 	printf(_("      --auth-local=METHOD   default authentication method for local-socket connections\n"));
+	printf(_("      --collation-provider={libc|icu}\n"
+			 "                            set default collation provider for new databases\n"));
 	printf(_(" [-D, --pgdata=]DATADIR     location for this database cluster\n"));
 	printf(_("  -E, --encoding=ENCODING   set default encoding for new databases\n"));
 	printf(_("  -g, --allow-group-access  allow group read/execute on data directory\n"));
+	printf(_("      --icu-locale          set ICU locale for new databases\n"));
 	printf(_("  -k, --data-checksums      use data page checksums\n"));
 	printf(_("      --locale=LOCALE       set default locale for new databases\n"));
 	printf(_("      --lc-collate=, --lc-ctype=, --lc-messages=LOCALE\n"
@@ -2353,7 +2384,8 @@ setup_locale_encoding(void)
 		strcmp(lc_ctype, lc_time) == 0 &&
 		strcmp(lc_ctype, lc_numeric) == 0 &&
 		strcmp(lc_ctype, lc_monetary) == 0 &&
-		strcmp(lc_ctype, lc_messages) == 0)
+		strcmp(lc_ctype, lc_messages) == 0 &&
+		(!icu_locale || strcmp(lc_ctype, icu_locale) == 0))
 		printf(_("The database cluster will be initialized with locale \"%s\".\n"), lc_ctype);
 	else
 	{
@@ -2370,9 +2402,13 @@ setup_locale_encoding(void)
 			   lc_monetary,
 			   lc_numeric,
 			   lc_time);
+		if (icu_locale)
+			printf(_("  ICU:      %s\n"), icu_locale);
 	}
 
-	if (!encoding)
+	if (!encoding && collation_provider[0] == COLLPROVIDER_ICU)
+		encodingid = PG_UTF8;
+	else if (!encoding)
 	{
 		int			ctype_enc;
 
@@ -2876,6 +2912,8 @@ main(int argc, char *argv[])
 		{"data-checksums", no_argument, NULL, 'k'},
 		{"allow-group-access", no_argument, NULL, 'g'},
 		{"discard-caches", no_argument, NULL, 14},
+		{"collation-provider", required_argument, NULL, 15},
+		{"icu-locale", required_argument, NULL, 16},
 		{NULL, 0, NULL, 0}
 	};
 
@@ -3022,6 +3060,20 @@ main(int argc, char *argv[])
 										 extra_options,
 										 "-c debug_discard_caches=1");
 				break;
+			case 15:
+				if (strcmp(optarg, "icu") == 0)
+					collation_provider[0] = COLLPROVIDER_ICU;
+				else if (strcmp(optarg, "libc") == 0)
+					collation_provider[0] = COLLPROVIDER_LIBC;
+				else
+				{
+					pg_log_error("unrecognized collation provider: %s", optarg);
+					exit(1);
+				}
+				break;
+			case 16:
+				icu_locale = pg_strdup(optarg);
+				break;
 			default:
 				/* getopt_long already emitted a complaint */
 				fprintf(stderr, _("Try \"%s --help\" for more information.\n"),
diff --git a/src/bin/initdb/t/001_initdb.pl b/src/bin/initdb/t/001_initdb.pl
index 6796d8520e..6b3208a03d 100644
--- a/src/bin/initdb/t/001_initdb.pl
+++ b/src/bin/initdb/t/001_initdb.pl
@@ -11,7 +11,7 @@
 use File::stat qw{lstat};
 use PostgreSQL::Test::Cluster;
 use PostgreSQL::Test::Utils;
-use Test::More tests => 22;
+use Test::More tests => 24;
 
 my $tempdir = PostgreSQL::Test::Utils::tempdir;
 my $xlogdir = "$tempdir/pgxlog";
@@ -92,3 +92,19 @@
 	ok(check_mode_recursive($datadir_group, 0750, 0640),
 		'check PGDATA permissions');
 }
+
+# Collation provider tests
+
+if ($ENV{with_icu} eq 'yes')
+{
+	command_ok(['initdb', '--no-sync', '--collation-provider=icu', "$tempdir/data2"],
+			   'collation provider ICU');
+}
+else
+{
+	command_fails(['initdb', '--no-sync', '--collation-provider=icu', "$tempdir/data2"],
+				  'collation provider ICU fails since no ICU support');
+}
+
+command_fails(['initdb', '--no-sync', '--collation-provider=xyz', "$tempdir/dataX"],
+			  'fails for invalid collation provider');
diff --git a/src/bin/pg_dump/pg_dump.c b/src/bin/pg_dump/pg_dump.c
index b52f3ccda2..7c6af8d2ef 100644
--- a/src/bin/pg_dump/pg_dump.c
+++ b/src/bin/pg_dump/pg_dump.c
@@ -2740,6 +2740,7 @@ dumpDatabase(Archive *fout)
 				i_datname,
 				i_dba,
 				i_encoding,
+				i_datcollprovider,
 				i_collate,
 				i_ctype,
 				i_frozenxid,
@@ -2755,6 +2756,7 @@ dumpDatabase(Archive *fout)
 	const char *datname,
 			   *dba,
 			   *encoding,
+			   *datcollprovider,
 			   *collate,
 			   *ctype,
 			   *datistemplate,
@@ -2774,6 +2776,7 @@ dumpDatabase(Archive *fout)
 		appendPQExpBuffer(dbQry, "SELECT tableoid, oid, datname, "
 						  "(%s datdba) AS dba, "
 						  "pg_encoding_to_char(encoding) AS encoding, "
+						  "datcollprovider, "
 						  "datcollate, datctype, datfrozenxid, datminmxid, "
 						  "datacl, acldefault('d', datdba) AS acldefault, "
 						  "datistemplate, datconnlimit, "
@@ -2807,6 +2810,7 @@ dumpDatabase(Archive *fout)
 	i_datname = PQfnumber(res, "datname");
 	i_dba = PQfnumber(res, "dba");
 	i_encoding = PQfnumber(res, "encoding");
+	i_datcollprovider = PQfnumber(res, "datcollprovider");
 	i_collate = PQfnumber(res, "datcollate");
 	i_ctype = PQfnumber(res, "datctype");
 	i_frozenxid = PQfnumber(res, "datfrozenxid");
@@ -2822,6 +2826,7 @@ dumpDatabase(Archive *fout)
 	datname = PQgetvalue(res, 0, i_datname);
 	dba = PQgetvalue(res, 0, i_dba);
 	encoding = PQgetvalue(res, 0, i_encoding);
+	datcollprovider = PQgetvalue(res, 0, i_datcollprovider);
 	collate = PQgetvalue(res, 0, i_collate);
 	ctype = PQgetvalue(res, 0, i_ctype);
 	frozenxid = atooid(PQgetvalue(res, 0, i_frozenxid));
@@ -2847,6 +2852,17 @@ dumpDatabase(Archive *fout)
 		appendPQExpBufferStr(creaQry, " ENCODING = ");
 		appendStringLiteralAH(creaQry, encoding, fout);
 	}
+	if (strlen(datcollprovider) > 0)
+	{
+		appendPQExpBufferStr(creaQry, " COLLATION_PROVIDER = ");
+		if (datcollprovider[0] == 'c')
+			appendPQExpBufferStr(creaQry, "libc");
+		else if (datcollprovider[0] == 'i')
+			appendPQExpBufferStr(creaQry, "icu");
+		else
+			fatal("unrecognized collation provider: %s",
+				  datcollprovider);
+	}
 	if (strlen(collate) > 0 && strcmp(collate, ctype) == 0)
 	{
 		appendPQExpBufferStr(creaQry, " LOCALE = ");
diff --git a/src/bin/psql/describe.c b/src/bin/psql/describe.c
index c28788e84f..0d710bd47e 100644
--- a/src/bin/psql/describe.c
+++ b/src/bin/psql/describe.c
@@ -896,6 +896,18 @@ listAllDbs(const char *pattern, bool verbose)
 					  gettext_noop("Encoding"),
 					  gettext_noop("Collate"),
 					  gettext_noop("Ctype"));
+	if (pset.sversion >= 150000)
+		appendPQExpBuffer(&buf,
+						  "       d.daticucoll as \"%s\",\n"
+						  "       CASE d.datcollprovider WHEN 'c' THEN 'libc' WHEN 'i' THEN 'icu' END AS \"%s\",\n",
+						  gettext_noop("ICU Collation"),
+						  gettext_noop("Coll. Provider"));
+	else
+		appendPQExpBuffer(&buf,
+						  "       d.datcollate as \"%s\",\n"
+						  "       'libc' AS \"%s\",\n",
+						  gettext_noop("ICU Collation"),
+						  gettext_noop("Coll. Provider"));
 	appendPQExpBufferStr(&buf, "       ");
 	printACLColumn(&buf, "d.datacl");
 	if (verbose)
@@ -4573,7 +4585,7 @@ listCollations(const char *pattern, bool verbose, bool showSystem)
 	PQExpBufferData buf;
 	PGresult   *res;
 	printQueryOpt myopt = pset.popt;
-	static const bool translate_columns[] = {false, false, false, false, false, true, false};
+	static const bool translate_columns[] = {false, false, false, false, false, false, true, false};
 
 	initPQExpBuffer(&buf);
 
@@ -4587,6 +4599,15 @@ listCollations(const char *pattern, bool verbose, bool showSystem)
 					  gettext_noop("Collate"),
 					  gettext_noop("Ctype"));
 
+	if (pset.sversion >= 150000)
+		appendPQExpBuffer(&buf,
+						  ",\n       c.collicucoll AS \"%s\"",
+						  gettext_noop("ICU Collation"));
+	else
+		appendPQExpBuffer(&buf,
+						  ",\n       c.collcollate AS \"%s\"",
+						  gettext_noop("ICU Collation"));
+
 	if (pset.sversion >= 100000)
 		appendPQExpBuffer(&buf,
 						  ",\n       CASE c.collprovider WHEN 'd' THEN 'default' WHEN 'c' THEN 'libc' WHEN 'i' THEN 'icu' END AS \"%s\"",
diff --git a/src/bin/psql/tab-complete.c b/src/bin/psql/tab-complete.c
index cf30239f6d..7db4a68df6 100644
--- a/src/bin/psql/tab-complete.c
+++ b/src/bin/psql/tab-complete.c
@@ -2587,7 +2587,7 @@ psql_completion(const char *text, int start, int end)
 		COMPLETE_WITH("OWNER", "TEMPLATE", "ENCODING", "TABLESPACE",
 					  "IS_TEMPLATE",
 					  "ALLOW_CONNECTIONS", "CONNECTION LIMIT",
-					  "LC_COLLATE", "LC_CTYPE", "LOCALE");
+					  "LC_COLLATE", "LC_CTYPE", "LOCALE", "COLLATION_PROVIDER");
 
 	else if (Matches("CREATE", "DATABASE", MatchAny, "TEMPLATE"))
 		COMPLETE_WITH_QUERY(Query_for_list_of_template_databases);
diff --git a/src/bin/scripts/Makefile b/src/bin/scripts/Makefile
index b8d7cf2f2d..342a57d71b 100644
--- a/src/bin/scripts/Makefile
+++ b/src/bin/scripts/Makefile
@@ -53,6 +53,8 @@ clean distclean maintainer-clean:
 	rm -f common.o $(WIN32RES)
 	rm -rf tmp_check
 
+export with_icu
+
 check:
 	$(prove_check)
 
diff --git a/src/bin/scripts/createdb.c b/src/bin/scripts/createdb.c
index 041454f075..1944580f36 100644
--- a/src/bin/scripts/createdb.c
+++ b/src/bin/scripts/createdb.c
@@ -38,6 +38,7 @@ main(int argc, char *argv[])
 		{"lc-ctype", required_argument, NULL, 2},
 		{"locale", required_argument, NULL, 'l'},
 		{"maintenance-db", required_argument, NULL, 3},
+		{"collation-provider", required_argument, NULL, 4},
 		{NULL, 0, NULL, 0}
 	};
 
@@ -61,6 +62,7 @@ main(int argc, char *argv[])
 	char	   *lc_collate = NULL;
 	char	   *lc_ctype = NULL;
 	char	   *locale = NULL;
+	char	   *collation_provider = NULL;
 
 	PQExpBufferData sql;
 
@@ -119,6 +121,9 @@ main(int argc, char *argv[])
 			case 3:
 				maintenance_db = pg_strdup(optarg);
 				break;
+			case 4:
+				collation_provider = pg_strdup(optarg);
+				break;
 			default:
 				fprintf(stderr, _("Try \"%s --help\" for more information.\n"), progname);
 				exit(1);
@@ -217,6 +222,8 @@ main(int argc, char *argv[])
 		appendPQExpBufferStr(&sql, " LC_CTYPE ");
 		appendStringLiteralConn(&sql, lc_ctype, conn);
 	}
+	if (collation_provider)
+		appendPQExpBuffer(&sql, " COLLATION_PROVIDER %s", collation_provider);
 
 	appendPQExpBufferChar(&sql, ';');
 
@@ -267,6 +274,8 @@ help(const char *progname)
 	printf(_("Usage:\n"));
 	printf(_("  %s [OPTION]... [DBNAME] [DESCRIPTION]\n"), progname);
 	printf(_("\nOptions:\n"));
+	printf(_("      --collation-provider={libc|icu}\n"
+			 "                               collation provider for the database's default collation\n"));
 	printf(_("  -D, --tablespace=TABLESPACE  default tablespace for the database\n"));
 	printf(_("  -e, --echo                   show the commands being sent to the server\n"));
 	printf(_("  -E, --encoding=ENCODING      encoding for the database\n"));
diff --git a/src/bin/scripts/t/020_createdb.pl b/src/bin/scripts/t/020_createdb.pl
index 6bcc59de08..e1a4af384c 100644
--- a/src/bin/scripts/t/020_createdb.pl
+++ b/src/bin/scripts/t/020_createdb.pl
@@ -6,7 +6,7 @@
 
 use PostgreSQL::Test::Cluster;
 use PostgreSQL::Test::Utils;
-use Test::More tests => 25;
+use Test::More tests => 28;
 
 program_help_ok('createdb');
 program_version_ok('createdb');
@@ -25,9 +25,27 @@
 	qr/statement: CREATE DATABASE foobar2 ENCODING 'LATIN1'/,
 	'create database with encoding');
 
+if ($ENV{with_icu} eq 'yes')
+{
+	$node->issues_sql_like(
+		[ 'createdb', '-T', 'template0', '--collation-provider=icu', 'foobar4' ],
+		qr/statement: CREATE DATABASE foobar4 .* COLLATION_PROVIDER icu/,
+		'create database with ICU');
+}
+else
+{
+	$node->command_fails(
+		[ 'createdb', '-T', 'template0', '--collation-provider=icu', 'foobar4' ],
+		'create database with ICU fails since no ICU support');
+	pass;
+}
+
 $node->command_fails([ 'createdb', 'foobar1' ],
 	'fails if database already exists');
 
+$node->command_fails([ 'createdb', '-T', 'template0', '--collation-provider=xyz', 'foobarX' ],
+	'fails for invalid collation provider');
+
 # Check use of templates with shared dependencies copied from the template.
 my ($ret, $stdout, $stderr) = $node->psql(
 	'foobar2',
diff --git a/src/include/catalog/pg_collation.dat b/src/include/catalog/pg_collation.dat
index 6e0ab1ab4b..2a8cf2be7c 100644
--- a/src/include/catalog/pg_collation.dat
+++ b/src/include/catalog/pg_collation.dat
@@ -14,8 +14,7 @@
 
 { oid => '100', oid_symbol => 'DEFAULT_COLLATION_OID',
   descr => 'database\'s default collation',
-  collname => 'default', collprovider => 'd', collencoding => '-1',
-  collcollate => '', collctype => '' },
+  collname => 'default', collprovider => 'd', collencoding => '-1' },
 { oid => '950', oid_symbol => 'C_COLLATION_OID',
   descr => 'standard C collation',
   collname => 'C', collprovider => 'c', collencoding => '-1',
diff --git a/src/include/catalog/pg_collation.h b/src/include/catalog/pg_collation.h
index 03bd4cb5d4..bff59abe92 100644
--- a/src/include/catalog/pg_collation.h
+++ b/src/include/catalog/pg_collation.h
@@ -39,9 +39,10 @@ CATALOG(pg_collation,3456,CollationRelationId)
 	char		collprovider;	/* see constants below */
 	bool		collisdeterministic BKI_DEFAULT(t);
 	int32		collencoding;	/* encoding for this collation; -1 = "all" */
-	NameData	collcollate;	/* LC_COLLATE setting */
-	NameData	collctype;		/* LC_CTYPE setting */
 #ifdef CATALOG_VARLEN			/* variable-length fields start here */
+	text		collcollate BKI_DEFAULT(_null_);	/* LC_COLLATE setting */
+	text		collctype BKI_DEFAULT(_null_);		/* LC_CTYPE setting */
+	text		collicucoll BKI_DEFAULT(_null_);	/* ICU collation string */
 	text		collversion BKI_DEFAULT(_null_);	/* provider-dependent
 													 * version of collation
 													 * data */
@@ -75,6 +76,7 @@ extern Oid	CollationCreate(const char *collname, Oid collnamespace,
 							bool collisdeterministic,
 							int32 collencoding,
 							const char *collcollate, const char *collctype,
+							const char *collicucoll,
 							const char *collversion,
 							bool if_not_exists,
 							bool quiet);
diff --git a/src/include/catalog/pg_database.dat b/src/include/catalog/pg_database.dat
index b8aa1364a0..6c62efcc54 100644
--- a/src/include/catalog/pg_database.dat
+++ b/src/include/catalog/pg_database.dat
@@ -15,7 +15,7 @@
 { oid => '1', oid_symbol => 'TemplateDbOid',
   descr => 'default template for new databases',
   datname => 'template1', encoding => 'ENCODING', datcollate => 'LC_COLLATE',
-  datctype => 'LC_CTYPE', datistemplate => 't', datallowconn => 't',
+  datctype => 'LC_CTYPE', daticucoll => 'ICUCOLL', datcollprovider => 'COLLPROVIDER', datistemplate => 't', datallowconn => 't',
   datconnlimit => '-1', datlastsysoid => '0', datfrozenxid => '0',
   datminmxid => '1', dattablespace => 'pg_default', datacl => '_null_' },
 
diff --git a/src/include/catalog/pg_database.h b/src/include/catalog/pg_database.h
index 43f3beb6a3..9280850185 100644
--- a/src/include/catalog/pg_database.h
+++ b/src/include/catalog/pg_database.h
@@ -40,11 +40,8 @@ CATALOG(pg_database,1262,DatabaseRelationId) BKI_SHARED_RELATION BKI_ROWTYPE_OID
 	/* character encoding */
 	int32		encoding;
 
-	/* LC_COLLATE setting */
-	NameData	datcollate;
-
-	/* LC_CTYPE setting */
-	NameData	datctype;
+	/* see pg_collation.collprovider */
+	char		datcollprovider;
 
 	/* allowed as CREATE DATABASE template? */
 	bool		datistemplate;
@@ -68,6 +65,15 @@ CATALOG(pg_database,1262,DatabaseRelationId) BKI_SHARED_RELATION BKI_ROWTYPE_OID
 	Oid			dattablespace BKI_LOOKUP(pg_tablespace);
 
 #ifdef CATALOG_VARLEN			/* variable-length fields start here */
+	/* LC_COLLATE setting */
+	text		datcollate BKI_FORCE_NOT_NULL;
+
+	/* LC_CTYPE setting */
+	text		datctype BKI_FORCE_NOT_NULL;
+
+	/* ICU collation */
+	text		daticucoll;
+
 	/* access permissions */
 	aclitem		datacl[1];
 #endif
diff --git a/src/include/utils/pg_locale.h b/src/include/utils/pg_locale.h
index 2946f46c76..19478e573f 100644
--- a/src/include/utils/pg_locale.h
+++ b/src/include/utils/pg_locale.h
@@ -101,6 +101,12 @@ struct pg_locale_struct
 
 typedef struct pg_locale_struct *pg_locale_t;
 
+extern struct pg_locale_struct default_locale;
+
+extern void make_icu_collator(const char *icucollstr,
+							  struct pg_locale_struct *resultp);
+extern void check_collation_version(HeapTuple colltuple);
+
 extern pg_locale_t pg_newlocale_from_collation(Oid collid);
 
 extern char *get_collation_actual_version(char collprovider, const char *collcollate);
diff --git a/src/test/regress/expected/collate.icu.utf8.out b/src/test/regress/expected/collate.icu.utf8.out
index 70133df804..3d9647b597 100644
--- a/src/test/regress/expected/collate.icu.utf8.out
+++ b/src/test/regress/expected/collate.icu.utf8.out
@@ -1029,14 +1029,12 @@ CREATE COLLATION test0 FROM "C"; -- fail, duplicate name
 ERROR:  collation "test0" already exists
 do $$
 BEGIN
-  EXECUTE 'CREATE COLLATION test1 (provider = icu, lc_collate = ' ||
-          quote_literal(current_setting('lc_collate')) ||
-          ', lc_ctype = ' ||
-          quote_literal(current_setting('lc_ctype')) || ');';
+  EXECUTE 'CREATE COLLATION test1 (provider = icu, locale = ' ||
+          quote_literal(current_setting('lc_collate')) || ');';
 END
 $$;
-CREATE COLLATION test3 (provider = icu, lc_collate = 'en_US.utf8'); -- fail, need lc_ctype
-ERROR:  parameter "lc_ctype" must be specified
+CREATE COLLATION test3 (provider = icu, lc_collate = 'en_US.utf8'); -- fail, needs "locale"
+ERROR:  parameter "locale" must be specified
 CREATE COLLATION testx (provider = icu, locale = 'nonsense'); /* never fails with ICU */  DROP COLLATION testx;
 CREATE COLLATION test4 FROM nonsense;
 ERROR:  collation "nonsense" for encoding "UTF8" does not exist
diff --git a/src/test/regress/sql/collate.icu.utf8.sql b/src/test/regress/sql/collate.icu.utf8.sql
index 9cee3d0042..0677ba56e4 100644
--- a/src/test/regress/sql/collate.icu.utf8.sql
+++ b/src/test/regress/sql/collate.icu.utf8.sql
@@ -366,13 +366,11 @@ CREATE SCHEMA test_schema;
 CREATE COLLATION test0 FROM "C"; -- fail, duplicate name
 do $$
 BEGIN
-  EXECUTE 'CREATE COLLATION test1 (provider = icu, lc_collate = ' ||
-          quote_literal(current_setting('lc_collate')) ||
-          ', lc_ctype = ' ||
-          quote_literal(current_setting('lc_ctype')) || ');';
+  EXECUTE 'CREATE COLLATION test1 (provider = icu, locale = ' ||
+          quote_literal(current_setting('lc_collate')) || ');';
 END
 $$;
-CREATE COLLATION test3 (provider = icu, lc_collate = 'en_US.utf8'); -- fail, need lc_ctype
+CREATE COLLATION test3 (provider = icu, lc_collate = 'en_US.utf8'); -- fail, needs "locale"
 CREATE COLLATION testx (provider = icu, locale = 'nonsense'); /* never fails with ICU */  DROP COLLATION testx;
 
 CREATE COLLATION test4 FROM nonsense;

base-commit: 8112bcf0cc602e00e95eab6c4bdc0eb73b5b547d
-- 
2.34.1

From 2ee4b77221020e81ec83cf37d36e3955bf619d80 Mon Sep 17 00:00:00 2001
From: Peter Eisentraut <peter@eisentraut.org>
Date: Thu, 13 Jan 2022 09:14:41 +0100
Subject: [PATCH] Call pg_newlocale_from_collation() also with default
 collation

Previously, callers of pg_newlocale_from_collation() did not call it
if the collation was DEFAULT_COLLATION_OID and instead proceeded with
a pg_locale_t of 0.  Instead, now we call it anyway and have it return
0 if the default collation was passed.  It already did this, so we
just have to adjust the callers.  This simplifies all the call sites
and also makes future enhancements easier.

After discussion and testing, the previous comment in pg_locale.c
about avoiding this for performance reasons may have been mistaken
since it was testing a very different patch version way back when.

Discussion: https://www.postgresql.org/message-id/ed3baa81-7fac-7788-cc12-41e3f7917e34@enterprisedb.com
---
 src/backend/access/hash/hashfunc.c   |  4 +-
 src/backend/regex/regc_pg_locale.c   | 40 ++++++------
 src/backend/utils/adt/formatting.c   | 96 +++++++++++++---------------
 src/backend/utils/adt/like.c         | 37 ++++++-----
 src/backend/utils/adt/like_support.c | 27 ++++----
 src/backend/utils/adt/pg_locale.c    |  3 -
 src/backend/utils/adt/varchar.c      | 26 +++++---
 src/backend/utils/adt/varlena.c      | 34 ++++++----
 8 files changed, 135 insertions(+), 132 deletions(-)

diff --git a/src/backend/access/hash/hashfunc.c b/src/backend/access/hash/hashfunc.c
index 0521c69dd5..b57ed946c4 100644
--- a/src/backend/access/hash/hashfunc.c
+++ b/src/backend/access/hash/hashfunc.c
@@ -278,7 +278,7 @@ hashtext(PG_FUNCTION_ARGS)
 				 errmsg("could not determine which collation to use for string hashing"),
 				 errhint("Use the COLLATE clause to set the collation explicitly.")));
 
-	if (!lc_collate_is_c(collid) && collid != DEFAULT_COLLATION_OID)
+	if (!lc_collate_is_c(collid))
 		mylocale = pg_newlocale_from_collation(collid);
 
 	if (!mylocale || mylocale->deterministic)
@@ -334,7 +334,7 @@ hashtextextended(PG_FUNCTION_ARGS)
 				 errmsg("could not determine which collation to use for string hashing"),
 				 errhint("Use the COLLATE clause to set the collation explicitly.")));
 
-	if (!lc_collate_is_c(collid) && collid != DEFAULT_COLLATION_OID)
+	if (!lc_collate_is_c(collid))
 		mylocale = pg_newlocale_from_collation(collid);
 
 	if (!mylocale || mylocale->deterministic)
diff --git a/src/backend/regex/regc_pg_locale.c b/src/backend/regex/regc_pg_locale.c
index e0d93eab32..6e84f42cb2 100644
--- a/src/backend/regex/regc_pg_locale.c
+++ b/src/backend/regex/regc_pg_locale.c
@@ -231,6 +231,18 @@ static const unsigned char pg_char_properties[128] = {
 void
 pg_set_regex_collation(Oid collation)
 {
+	if (!OidIsValid(collation))
+	{
+		/*
+		 * This typically means that the parser could not resolve a
+		 * conflict of implicit collations, so report it that way.
+		 */
+		ereport(ERROR,
+				(errcode(ERRCODE_INDETERMINATE_COLLATION),
+				 errmsg("could not determine which collation to use for regular expression"),
+				 errhint("Use the COLLATE clause to set the collation explicitly.")));
+	}
+
 	if (lc_ctype_is_c(collation))
 	{
 		/* C/POSIX collations use this path regardless of database encoding */
@@ -240,28 +252,12 @@ pg_set_regex_collation(Oid collation)
 	}
 	else
 	{
-		if (collation == DEFAULT_COLLATION_OID)
-			pg_regex_locale = 0;
-		else if (OidIsValid(collation))
-		{
-			/*
-			 * NB: pg_newlocale_from_collation will fail if not HAVE_LOCALE_T;
-			 * the case of pg_regex_locale != 0 but not HAVE_LOCALE_T does not
-			 * have to be considered below.
-			 */
-			pg_regex_locale = pg_newlocale_from_collation(collation);
-		}
-		else
-		{
-			/*
-			 * This typically means that the parser could not resolve a
-			 * conflict of implicit collations, so report it that way.
-			 */
-			ereport(ERROR,
-					(errcode(ERRCODE_INDETERMINATE_COLLATION),
-					 errmsg("could not determine which collation to use for regular expression"),
-					 errhint("Use the COLLATE clause to set the collation explicitly.")));
-		}
+		/*
+		 * NB: pg_newlocale_from_collation will fail if not HAVE_LOCALE_T;
+		 * the case of pg_regex_locale != 0 but not HAVE_LOCALE_T does not
+		 * have to be considered below.
+		 */
+		pg_regex_locale = pg_newlocale_from_collation(collation);
 
 		if (pg_regex_locale && !pg_regex_locale->deterministic)
 			ereport(ERROR,
diff --git a/src/backend/utils/adt/formatting.c b/src/backend/utils/adt/formatting.c
index e8f996ac83..d4c2e7b069 100644
--- a/src/backend/utils/adt/formatting.c
+++ b/src/backend/utils/adt/formatting.c
@@ -1641,6 +1641,19 @@ str_tolower(const char *buff, size_t nbytes, Oid collid)
 	if (!buff)
 		return NULL;
 
+	if (!OidIsValid(collid))
+	{
+		/*
+		 * This typically means that the parser could not resolve a
+		 * conflict of implicit collations, so report it that way.
+		 */
+		ereport(ERROR,
+				(errcode(ERRCODE_INDETERMINATE_COLLATION),
+				 errmsg("could not determine which collation to use for %s function",
+						"lower()"),
+				 errhint("Use the COLLATE clause to set the collation explicitly.")));
+	}
+
 	/* C/POSIX collations use this path regardless of database encoding */
 	if (lc_ctype_is_c(collid))
 	{
@@ -1648,24 +1661,9 @@ str_tolower(const char *buff, size_t nbytes, Oid collid)
 	}
 	else
 	{
-		pg_locale_t mylocale = 0;
+		pg_locale_t mylocale;
 
-		if (collid != DEFAULT_COLLATION_OID)
-		{
-			if (!OidIsValid(collid))
-			{
-				/*
-				 * This typically means that the parser could not resolve a
-				 * conflict of implicit collations, so report it that way.
-				 */
-				ereport(ERROR,
-						(errcode(ERRCODE_INDETERMINATE_COLLATION),
-						 errmsg("could not determine which collation to use for %s function",
-								"lower()"),
-						 errhint("Use the COLLATE clause to set the collation explicitly.")));
-			}
-			mylocale = pg_newlocale_from_collation(collid);
-		}
+		mylocale = pg_newlocale_from_collation(collid);
 
 #ifdef USE_ICU
 		if (mylocale && mylocale->provider == COLLPROVIDER_ICU)
@@ -1765,6 +1763,19 @@ str_toupper(const char *buff, size_t nbytes, Oid collid)
 	if (!buff)
 		return NULL;
 
+	if (!OidIsValid(collid))
+	{
+		/*
+		 * This typically means that the parser could not resolve a
+		 * conflict of implicit collations, so report it that way.
+		 */
+		ereport(ERROR,
+				(errcode(ERRCODE_INDETERMINATE_COLLATION),
+				 errmsg("could not determine which collation to use for %s function",
+						"upper()"),
+				 errhint("Use the COLLATE clause to set the collation explicitly.")));
+	}
+
 	/* C/POSIX collations use this path regardless of database encoding */
 	if (lc_ctype_is_c(collid))
 	{
@@ -1772,24 +1783,9 @@ str_toupper(const char *buff, size_t nbytes, Oid collid)
 	}
 	else
 	{
-		pg_locale_t mylocale = 0;
+		pg_locale_t mylocale;
 
-		if (collid != DEFAULT_COLLATION_OID)
-		{
-			if (!OidIsValid(collid))
-			{
-				/*
-				 * This typically means that the parser could not resolve a
-				 * conflict of implicit collations, so report it that way.
-				 */
-				ereport(ERROR,
-						(errcode(ERRCODE_INDETERMINATE_COLLATION),
-						 errmsg("could not determine which collation to use for %s function",
-								"upper()"),
-						 errhint("Use the COLLATE clause to set the collation explicitly.")));
-			}
-			mylocale = pg_newlocale_from_collation(collid);
-		}
+		mylocale = pg_newlocale_from_collation(collid);
 
 #ifdef USE_ICU
 		if (mylocale && mylocale->provider == COLLPROVIDER_ICU)
@@ -1890,6 +1886,19 @@ str_initcap(const char *buff, size_t nbytes, Oid collid)
 	if (!buff)
 		return NULL;
 
+	if (!OidIsValid(collid))
+	{
+		/*
+		 * This typically means that the parser could not resolve a
+		 * conflict of implicit collations, so report it that way.
+		 */
+		ereport(ERROR,
+				(errcode(ERRCODE_INDETERMINATE_COLLATION),
+				 errmsg("could not determine which collation to use for %s function",
+						"initcap()"),
+				 errhint("Use the COLLATE clause to set the collation explicitly.")));
+	}
+
 	/* C/POSIX collations use this path regardless of database encoding */
 	if (lc_ctype_is_c(collid))
 	{
@@ -1897,24 +1906,9 @@ str_initcap(const char *buff, size_t nbytes, Oid collid)
 	}
 	else
 	{
-		pg_locale_t mylocale = 0;
+		pg_locale_t mylocale;
 
-		if (collid != DEFAULT_COLLATION_OID)
-		{
-			if (!OidIsValid(collid))
-			{
-				/*
-				 * This typically means that the parser could not resolve a
-				 * conflict of implicit collations, so report it that way.
-				 */
-				ereport(ERROR,
-						(errcode(ERRCODE_INDETERMINATE_COLLATION),
-						 errmsg("could not determine which collation to use for %s function",
-								"initcap()"),
-						 errhint("Use the COLLATE clause to set the collation explicitly.")));
-			}
-			mylocale = pg_newlocale_from_collation(collid);
-		}
+		mylocale = pg_newlocale_from_collation(collid);
 
 #ifdef USE_ICU
 		if (mylocale && mylocale->provider == COLLPROVIDER_ICU)
diff --git a/src/backend/utils/adt/like.c b/src/backend/utils/adt/like.c
index 9f241dc7c6..833ee8f814 100644
--- a/src/backend/utils/adt/like.c
+++ b/src/backend/utils/adt/like.c
@@ -150,7 +150,7 @@ SB_lower_char(unsigned char c, pg_locale_t locale, bool locale_is_c)
 static inline int
 GenericMatchText(const char *s, int slen, const char *p, int plen, Oid collation)
 {
-	if (collation && !lc_ctype_is_c(collation) && collation != DEFAULT_COLLATION_OID)
+	if (collation && !lc_ctype_is_c(collation))
 	{
 		pg_locale_t locale = pg_newlocale_from_collation(collation);
 
@@ -178,28 +178,27 @@ Generic_Text_IC_like(text *str, text *pat, Oid collation)
 	pg_locale_t locale = 0;
 	bool		locale_is_c = false;
 
+	if (!OidIsValid(collation))
+	{
+		/*
+		 * This typically means that the parser could not resolve a
+		 * conflict of implicit collations, so report it that way.
+		 */
+		ereport(ERROR,
+				(errcode(ERRCODE_INDETERMINATE_COLLATION),
+				 errmsg("could not determine which collation to use for ILIKE"),
+				 errhint("Use the COLLATE clause to set the collation explicitly.")));
+	}
+
 	if (lc_ctype_is_c(collation))
 		locale_is_c = true;
-	else if (collation != DEFAULT_COLLATION_OID)
-	{
-		if (!OidIsValid(collation))
-		{
-			/*
-			 * This typically means that the parser could not resolve a
-			 * conflict of implicit collations, so report it that way.
-			 */
-			ereport(ERROR,
-					(errcode(ERRCODE_INDETERMINATE_COLLATION),
-					 errmsg("could not determine which collation to use for ILIKE"),
-					 errhint("Use the COLLATE clause to set the collation explicitly.")));
-		}
+	else
 		locale = pg_newlocale_from_collation(collation);
 
-		if (locale && !locale->deterministic)
-			ereport(ERROR,
-					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-					 errmsg("nondeterministic collations are not supported for ILIKE")));
-	}
+	if (locale && !locale->deterministic)
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				 errmsg("nondeterministic collations are not supported for ILIKE")));
 
 	/*
 	 * For efficiency reasons, in the single byte case we don't call lower()
diff --git a/src/backend/utils/adt/like_support.c b/src/backend/utils/adt/like_support.c
index 7ca2a01e49..65a57fc3c4 100644
--- a/src/backend/utils/adt/like_support.c
+++ b/src/backend/utils/adt/like_support.c
@@ -1012,24 +1012,23 @@ like_fixed_prefix(Const *patt_const, bool case_insensitive, Oid collation,
 					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
 					 errmsg("case insensitive matching not supported on type bytea")));
 
+		if (!OidIsValid(collation))
+		{
+			/*
+			 * This typically means that the parser could not resolve a
+			 * conflict of implicit collations, so report it that way.
+			 */
+			ereport(ERROR,
+					(errcode(ERRCODE_INDETERMINATE_COLLATION),
+					 errmsg("could not determine which collation to use for ILIKE"),
+					 errhint("Use the COLLATE clause to set the collation explicitly.")));
+		}
+
 		/* If case-insensitive, we need locale info */
 		if (lc_ctype_is_c(collation))
 			locale_is_c = true;
-		else if (collation != DEFAULT_COLLATION_OID)
-		{
-			if (!OidIsValid(collation))
-			{
-				/*
-				 * This typically means that the parser could not resolve a
-				 * conflict of implicit collations, so report it that way.
-				 */
-				ereport(ERROR,
-						(errcode(ERRCODE_INDETERMINATE_COLLATION),
-						 errmsg("could not determine which collation to use for ILIKE"),
-						 errhint("Use the COLLATE clause to set the collation explicitly.")));
-			}
+		else
 			locale = pg_newlocale_from_collation(collation);
-		}
 	}
 
 	if (typeid != BYTEAOID)
diff --git a/src/backend/utils/adt/pg_locale.c b/src/backend/utils/adt/pg_locale.c
index 18f3afdc62..33cccc5c6c 100644
--- a/src/backend/utils/adt/pg_locale.c
+++ b/src/backend/utils/adt/pg_locale.c
@@ -1454,8 +1454,6 @@ report_newlocale_failure(const char *localename)
  *
  * As a special optimization, the default/database collation returns 0.
  * Callers should then revert to the non-locale_t-enabled code path.
- * In fact, they shouldn't call this function at all when they are dealing
- * with the default locale.  That can save quite a bit in hotspots.
  * Also, callers should avoid calling this before going down a C/POSIX
  * fastpath, because such a fastpath should work even on platforms without
  * locale_t support in the C library.
@@ -1472,7 +1470,6 @@ pg_newlocale_from_collation(Oid collid)
 	/* Callers must pass a valid OID */
 	Assert(OidIsValid(collid));
 
-	/* Return 0 for "default" collation, just in case caller forgets */
 	if (collid == DEFAULT_COLLATION_OID)
 		return (pg_locale_t) 0;
 
diff --git a/src/backend/utils/adt/varchar.c b/src/backend/utils/adt/varchar.c
index 95f768c884..8b5b30ed71 100644
--- a/src/backend/utils/adt/varchar.c
+++ b/src/backend/utils/adt/varchar.c
@@ -743,15 +743,20 @@ bpchareq(PG_FUNCTION_ARGS)
 				len2;
 	bool		result;
 	Oid			collid = PG_GET_COLLATION();
+	bool		locale_is_c = false;
+	pg_locale_t	mylocale = 0;
 
 	check_collation_set(collid);
 
 	len1 = bcTruelen(arg1);
 	len2 = bcTruelen(arg2);
 
-	if (lc_collate_is_c(collid) ||
-		collid == DEFAULT_COLLATION_OID ||
-		pg_newlocale_from_collation(collid)->deterministic)
+	if (lc_collate_is_c(collid))
+		locale_is_c = true;
+	else
+		mylocale = pg_newlocale_from_collation(collid);
+
+	if (locale_is_c || !mylocale || mylocale->deterministic)
 	{
 		/*
 		 * Since we only care about equality or not-equality, we can avoid all
@@ -783,15 +788,20 @@ bpcharne(PG_FUNCTION_ARGS)
 				len2;
 	bool		result;
 	Oid			collid = PG_GET_COLLATION();
+	bool		locale_is_c = false;
+	pg_locale_t	mylocale = 0;
 
 	check_collation_set(collid);
 
 	len1 = bcTruelen(arg1);
 	len2 = bcTruelen(arg2);
 
-	if (lc_collate_is_c(collid) ||
-		collid == DEFAULT_COLLATION_OID ||
-		pg_newlocale_from_collation(collid)->deterministic)
+	if (lc_collate_is_c(collid))
+		locale_is_c = true;
+	else
+		mylocale = pg_newlocale_from_collation(collid);
+
+	if (locale_is_c || !mylocale || mylocale->deterministic)
 	{
 		/*
 		 * Since we only care about equality or not-equality, we can avoid all
@@ -996,7 +1006,7 @@ hashbpchar(PG_FUNCTION_ARGS)
 	keydata = VARDATA_ANY(key);
 	keylen = bcTruelen(key);
 
-	if (!lc_collate_is_c(collid) && collid != DEFAULT_COLLATION_OID)
+	if (!lc_collate_is_c(collid))
 		mylocale = pg_newlocale_from_collation(collid);
 
 	if (!mylocale || mylocale->deterministic)
@@ -1056,7 +1066,7 @@ hashbpcharextended(PG_FUNCTION_ARGS)
 	keydata = VARDATA_ANY(key);
 	keylen = bcTruelen(key);
 
-	if (!lc_collate_is_c(collid) && collid != DEFAULT_COLLATION_OID)
+	if (!lc_collate_is_c(collid))
 		mylocale = pg_newlocale_from_collation(collid);
 
 	if (!mylocale || mylocale->deterministic)
diff --git a/src/backend/utils/adt/varlena.c b/src/backend/utils/adt/varlena.c
index b3eb39761d..a8db8080e2 100644
--- a/src/backend/utils/adt/varlena.c
+++ b/src/backend/utils/adt/varlena.c
@@ -1200,7 +1200,7 @@ text_position_setup(text *t1, text *t2, Oid collid, TextPositionState *state)
 
 	check_collation_set(collid);
 
-	if (!lc_collate_is_c(collid) && collid != DEFAULT_COLLATION_OID)
+	if (!lc_collate_is_c(collid))
 		mylocale = pg_newlocale_from_collation(collid);
 
 	if (mylocale && !mylocale->deterministic)
@@ -1556,10 +1556,9 @@ varstr_cmp(const char *arg1, int len1, const char *arg2, int len2, Oid collid)
 		char		a2buf[TEXTBUFLEN];
 		char	   *a1p,
 				   *a2p;
-		pg_locale_t mylocale = 0;
+		pg_locale_t mylocale;
 
-		if (collid != DEFAULT_COLLATION_OID)
-			mylocale = pg_newlocale_from_collation(collid);
+		mylocale = pg_newlocale_from_collation(collid);
 
 		/*
 		 * memcmp() can't tell us which of two unequal strings sorts first,
@@ -1776,13 +1775,18 @@ Datum
 texteq(PG_FUNCTION_ARGS)
 {
 	Oid			collid = PG_GET_COLLATION();
+	bool		locale_is_c = false;
+	pg_locale_t	mylocale = 0;
 	bool		result;
 
 	check_collation_set(collid);
 
-	if (lc_collate_is_c(collid) ||
-		collid == DEFAULT_COLLATION_OID ||
-		pg_newlocale_from_collation(collid)->deterministic)
+	if (lc_collate_is_c(collid))
+		locale_is_c = true;
+	else
+		mylocale = pg_newlocale_from_collation(collid);
+
+	if (locale_is_c || !mylocale || mylocale->deterministic)
 	{
 		Datum		arg1 = PG_GETARG_DATUM(0);
 		Datum		arg2 = PG_GETARG_DATUM(1);
@@ -1830,13 +1834,18 @@ Datum
 textne(PG_FUNCTION_ARGS)
 {
 	Oid			collid = PG_GET_COLLATION();
+	bool		locale_is_c = false;
+	pg_locale_t	mylocale = 0;
 	bool		result;
 
 	check_collation_set(collid);
 
-	if (lc_collate_is_c(collid) ||
-		collid == DEFAULT_COLLATION_OID ||
-		pg_newlocale_from_collation(collid)->deterministic)
+	if (lc_collate_is_c(collid))
+		locale_is_c = true;
+	else
+		mylocale = pg_newlocale_from_collation(collid);
+
+	if (locale_is_c || !mylocale || mylocale->deterministic)
 	{
 		Datum		arg1 = PG_GETARG_DATUM(0);
 		Datum		arg2 = PG_GETARG_DATUM(1);
@@ -1947,7 +1956,7 @@ text_starts_with(PG_FUNCTION_ARGS)
 
 	check_collation_set(collid);
 
-	if (!lc_collate_is_c(collid) && collid != DEFAULT_COLLATION_OID)
+	if (!lc_collate_is_c(collid))
 		mylocale = pg_newlocale_from_collation(collid);
 
 	if (mylocale && !mylocale->deterministic)
@@ -2061,8 +2070,7 @@ varstr_sortsupport(SortSupport ssup, Oid typid, Oid collid)
 		 * we'll figure out the collation based on the locale id and cache the
 		 * result.
 		 */
-		if (collid != DEFAULT_COLLATION_OID)
-			locale = pg_newlocale_from_collation(collid);
+		locale = pg_newlocale_from_collation(collid);
 
 		/*
 		 * There is a further exception on Windows.  When the database
-- 
2.34.1

From 1c46bf3138ad42074971aa3130142236de7e63f7 Mon Sep 17 00:00:00 2001
From: Peter Eisentraut <peter@eisentraut.org>
Date: Fri, 21 Jan 2022 10:01:25 +0100
Subject: [PATCH] Change collate and ctype fields to type text

This changes the data type of the catalog fields datcollate, datctype,
collcollate, and collctype from name to text.  There wasn't ever a
really good reason for them to be of type name; presumably this was
just carried over from when they were fixed-size fields in pg_control,
first into the corresponding pg_database fields, and then to
pg_collation.  The values are not identifiers or object names, and we
don't ever look them up that way.

Changing to type text saves space in the typical case, since locale
names are typically less than 10 bytes long.  But it is also possible
that an ICU locale name with several customization options appended
could be longer than 63 bytes, so this also enables that case, which
was previously probably broken.

Discussion: https://www.postgresql.org/message-id/flat/5e756dd6-0e91-d778-96fd-b1bcb06c161a@2ndquadrant.com
---
 doc/src/sgml/catalogs.sgml           | 40 +++++++++++++--------------
 src/backend/catalog/pg_collation.c   | 10 ++-----
 src/backend/commands/collationcmds.c | 41 +++++++++++++++++++---------
 src/backend/commands/dbcommands.c    | 21 ++++++++++----
 src/backend/utils/adt/pg_locale.c    | 29 +++++++++++++-------
 src/backend/utils/init/postinit.c    | 11 ++++++--
 src/include/catalog/pg_collation.h   |  4 +--
 src/include/catalog/pg_database.h    | 12 ++++----
 src/include/utils/pg_locale.h        |  2 ++
 9 files changed, 104 insertions(+), 66 deletions(-)

diff --git a/doc/src/sgml/catalogs.sgml b/doc/src/sgml/catalogs.sgml
index 1e65c426b2..7d5b0b1656 100644
--- a/doc/src/sgml/catalogs.sgml
+++ b/doc/src/sgml/catalogs.sgml
@@ -2368,7 +2368,7 @@ <title><structname>pg_collation</structname> Columns</title>
 
      <row>
       <entry role="catalog_table_entry"><para role="column_definition">
-       <structfield>collcollate</structfield> <type>name</type>
+       <structfield>collcollate</structfield> <type>text</type>
       </para>
       <para>
        <symbol>LC_COLLATE</symbol> for this collation object
@@ -2377,7 +2377,7 @@ <title><structname>pg_collation</structname> Columns</title>
 
      <row>
       <entry role="catalog_table_entry"><para role="column_definition">
-       <structfield>collctype</structfield> <type>name</type>
+       <structfield>collctype</structfield> <type>text</type>
       </para>
       <para>
        <symbol>LC_CTYPE</symbol> for this collation object
@@ -2951,24 +2951,6 @@ <title><structname>pg_database</structname> Columns</title>
       </para></entry>
      </row>
 
-     <row>
-      <entry role="catalog_table_entry"><para role="column_definition">
-       <structfield>datcollate</structfield> <type>name</type>
-      </para>
-      <para>
-       LC_COLLATE for this database
-      </para></entry>
-     </row>
-
-     <row>
-      <entry role="catalog_table_entry"><para role="column_definition">
-       <structfield>datctype</structfield> <type>name</type>
-      </para>
-      <para>
-       LC_CTYPE for this database
-      </para></entry>
-     </row>
-
      <row>
       <entry role="catalog_table_entry"><para role="column_definition">
        <structfield>datistemplate</structfield> <type>bool</type>
@@ -3043,6 +3025,24 @@ <title><structname>pg_database</structname> Columns</title>
       </para></entry>
      </row>
 
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
+       <structfield>datcollate</structfield> <type>text</type>
+      </para>
+      <para>
+       LC_COLLATE for this database
+      </para></entry>
+     </row>
+
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
+       <structfield>datctype</structfield> <type>text</type>
+      </para>
+      <para>
+       LC_CTYPE for this database
+      </para></entry>
+     </row>
+
      <row>
       <entry role="catalog_table_entry"><para role="column_definition">
        <structfield>datacl</structfield> <type>aclitem[]</type>
diff --git a/src/backend/catalog/pg_collation.c b/src/backend/catalog/pg_collation.c
index 5be6600652..bfc02d3038 100644
--- a/src/backend/catalog/pg_collation.c
+++ b/src/backend/catalog/pg_collation.c
@@ -58,9 +58,7 @@ CollationCreate(const char *collname, Oid collnamespace,
 	HeapTuple	tup;
 	Datum		values[Natts_pg_collation];
 	bool		nulls[Natts_pg_collation];
-	NameData	name_name,
-				name_collate,
-				name_ctype;
+	NameData	name_name;
 	Oid			oid;
 	ObjectAddress myself,
 				referenced;
@@ -163,10 +161,8 @@ CollationCreate(const char *collname, Oid collnamespace,
 	values[Anum_pg_collation_collprovider - 1] = CharGetDatum(collprovider);
 	values[Anum_pg_collation_collisdeterministic - 1] = BoolGetDatum(collisdeterministic);
 	values[Anum_pg_collation_collencoding - 1] = Int32GetDatum(collencoding);
-	namestrcpy(&name_collate, collcollate);
-	values[Anum_pg_collation_collcollate - 1] = NameGetDatum(&name_collate);
-	namestrcpy(&name_ctype, collctype);
-	values[Anum_pg_collation_collctype - 1] = NameGetDatum(&name_ctype);
+	values[Anum_pg_collation_collcollate - 1] = CStringGetTextDatum(collcollate);
+	values[Anum_pg_collation_collctype - 1] = CStringGetTextDatum(collctype);
 	if (collversion)
 		values[Anum_pg_collation_collversion - 1] = CStringGetTextDatum(collversion);
 	else
diff --git a/src/backend/commands/collationcmds.c b/src/backend/commands/collationcmds.c
index 56748551de..12fc2316f9 100644
--- a/src/backend/commands/collationcmds.c
+++ b/src/backend/commands/collationcmds.c
@@ -129,18 +129,30 @@ DefineCollation(ParseState *pstate, List *names, List *parameters, bool if_not_e
 	{
 		Oid			collid;
 		HeapTuple	tp;
+		Datum		datum;
+		bool		isnull;
 
 		collid = get_collation_oid(defGetQualifiedName(fromEl), false);
 		tp = SearchSysCache1(COLLOID, ObjectIdGetDatum(collid));
 		if (!HeapTupleIsValid(tp))
 			elog(ERROR, "cache lookup failed for collation %u", collid);
 
-		collcollate = pstrdup(NameStr(((Form_pg_collation) GETSTRUCT(tp))->collcollate));
-		collctype = pstrdup(NameStr(((Form_pg_collation) GETSTRUCT(tp))->collctype));
 		collprovider = ((Form_pg_collation) GETSTRUCT(tp))->collprovider;
 		collisdeterministic = ((Form_pg_collation) GETSTRUCT(tp))->collisdeterministic;
 		collencoding = ((Form_pg_collation) GETSTRUCT(tp))->collencoding;
 
+		datum = SysCacheGetAttr(COLLOID, tp, Anum_pg_collation_collcollate, &isnull);
+		if (!isnull)
+			collcollate = TextDatumGetCString(datum);
+		else
+			collcollate = NULL;
+
+		datum = SysCacheGetAttr(COLLOID, tp, Anum_pg_collation_collctype, &isnull);
+		if (!isnull)
+			collctype = TextDatumGetCString(datum);
+		else
+			collctype = NULL;
+
 		ReleaseSysCache(tp);
 
 		/*
@@ -314,7 +326,7 @@ AlterCollation(AlterCollationStmt *stmt)
 	Oid			collOid;
 	HeapTuple	tup;
 	Form_pg_collation collForm;
-	Datum		collversion;
+	Datum		datum;
 	bool		isnull;
 	char	   *oldversion;
 	char	   *newversion;
@@ -332,11 +344,12 @@ AlterCollation(AlterCollationStmt *stmt)
 		elog(ERROR, "cache lookup failed for collation %u", collOid);
 
 	collForm = (Form_pg_collation) GETSTRUCT(tup);
-	collversion = SysCacheGetAttr(COLLOID, tup, Anum_pg_collation_collversion,
-								  &isnull);
-	oldversion = isnull ? NULL : TextDatumGetCString(collversion);
+	datum = SysCacheGetAttr(COLLOID, tup, Anum_pg_collation_collversion, &isnull);
+	oldversion = isnull ? NULL : TextDatumGetCString(datum);
 
-	newversion = get_collation_actual_version(collForm->collprovider, NameStr(collForm->collcollate));
+	datum = SysCacheGetAttr(COLLOID, tup, Anum_pg_collation_collcollate, &isnull);
+	Assert(!isnull);
+	newversion = get_collation_actual_version(collForm->collprovider, TextDatumGetCString(datum));
 
 	/* cannot change from NULL to non-NULL or vice versa */
 	if ((!oldversion && newversion) || (oldversion && !newversion))
@@ -383,8 +396,9 @@ pg_collation_actual_version(PG_FUNCTION_ARGS)
 {
 	Oid			collid = PG_GETARG_OID(0);
 	HeapTuple	tp;
-	char	   *collcollate;
 	char		collprovider;
+	Datum		datum;
+	bool		isnull;
 	char	   *version;
 
 	tp = SearchSysCache1(COLLOID, ObjectIdGetDatum(collid));
@@ -393,12 +407,13 @@ pg_collation_actual_version(PG_FUNCTION_ARGS)
 				(errcode(ERRCODE_UNDEFINED_OBJECT),
 				 errmsg("collation with OID %u does not exist", collid)));
 
-	collcollate = pstrdup(NameStr(((Form_pg_collation) GETSTRUCT(tp))->collcollate));
 	collprovider = ((Form_pg_collation) GETSTRUCT(tp))->collprovider;
 
-	ReleaseSysCache(tp);
+	datum = SysCacheGetAttr(COLLOID, tp, Anum_pg_collation_collcollate, &isnull);
+	Assert(!isnull);
+	version = get_collation_actual_version(collprovider, TextDatumGetCString(datum));
 
-	version = get_collation_actual_version(collprovider, collcollate);
+	ReleaseSysCache(tp);
 
 	if (version)
 		PG_RETURN_TEXT_P(cstring_to_text(version));
@@ -546,7 +561,7 @@ pg_import_system_collations(PG_FUNCTION_ARGS)
 #ifdef READ_LOCALE_A_OUTPUT
 	{
 		FILE	   *locale_a_handle;
-		char		localebuf[NAMEDATALEN]; /* we assume ASCII so this is fine */
+		char		localebuf[LOCALE_NAME_BUFLEN];
 		int			nvalid = 0;
 		Oid			collid;
 		CollAliasData *aliases;
@@ -570,7 +585,7 @@ pg_import_system_collations(PG_FUNCTION_ARGS)
 		{
 			size_t		len;
 			int			enc;
-			char		alias[NAMEDATALEN];
+			char		alias[LOCALE_NAME_BUFLEN];
 
 			len = strlen(localebuf);
 
diff --git a/src/backend/commands/dbcommands.c b/src/backend/commands/dbcommands.c
index da8345561d..65b420aea6 100644
--- a/src/backend/commands/dbcommands.c
+++ b/src/backend/commands/dbcommands.c
@@ -523,10 +523,8 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 		DirectFunctionCall1(namein, CStringGetDatum(dbname));
 	new_record[Anum_pg_database_datdba - 1] = ObjectIdGetDatum(datdba);
 	new_record[Anum_pg_database_encoding - 1] = Int32GetDatum(encoding);
-	new_record[Anum_pg_database_datcollate - 1] =
-		DirectFunctionCall1(namein, CStringGetDatum(dbcollate));
-	new_record[Anum_pg_database_datctype - 1] =
-		DirectFunctionCall1(namein, CStringGetDatum(dbctype));
+	new_record[Anum_pg_database_datcollate - 1] = CStringGetTextDatum(dbcollate);
+	new_record[Anum_pg_database_datctype - 1] = CStringGetTextDatum(dbctype);
 	new_record[Anum_pg_database_datistemplate - 1] = BoolGetDatum(dbistemplate);
 	new_record[Anum_pg_database_datallowconn - 1] = BoolGetDatum(dballowconnections);
 	new_record[Anum_pg_database_datconnlimit - 1] = Int32GetDatum(dbconnlimit);
@@ -1820,6 +1818,9 @@ get_db_info(const char *name, LOCKMODE lockmode,
 
 			if (strcmp(name, NameStr(dbform->datname)) == 0)
 			{
+				Datum		datum;
+				bool		isnull;
+
 				/* oid of the database */
 				if (dbIdP)
 					*dbIdP = dbOid;
@@ -1846,9 +1847,17 @@ get_db_info(const char *name, LOCKMODE lockmode,
 					*dbTablespace = dbform->dattablespace;
 				/* default locale settings for this database */
 				if (dbCollate)
-					*dbCollate = pstrdup(NameStr(dbform->datcollate));
+				{
+					datum = SysCacheGetAttr(DATABASEOID, tuple, Anum_pg_database_datcollate, &isnull);
+					Assert(!isnull);
+					*dbCollate = TextDatumGetCString(datum);
+				}
 				if (dbCtype)
-					*dbCtype = pstrdup(NameStr(dbform->datctype));
+				{
+					datum = SysCacheGetAttr(DATABASEOID, tuple, Anum_pg_database_datctype, &isnull);
+					Assert(!isnull);
+					*dbCtype = TextDatumGetCString(datum);
+				}
 				ReleaseSysCache(tuple);
 				result = true;
 				break;
diff --git a/src/backend/utils/adt/pg_locale.c b/src/backend/utils/adt/pg_locale.c
index 33cccc5c6c..aefa0818d0 100644
--- a/src/backend/utils/adt/pg_locale.c
+++ b/src/backend/utils/adt/pg_locale.c
@@ -179,7 +179,7 @@ pg_perm_setlocale(int category, const char *locale)
 	 */
 	if (category == LC_CTYPE)
 	{
-		static char save_lc_ctype[NAMEDATALEN + 20];
+		static char save_lc_ctype[LOCALE_NAME_BUFLEN];
 
 		/* copy setlocale() return value before callee invokes it again */
 		strlcpy(save_lc_ctype, result, sizeof(save_lc_ctype));
@@ -1288,17 +1288,21 @@ lookup_collation_cache(Oid collation, bool set_flags)
 	{
 		/* Attempt to set the flags */
 		HeapTuple	tp;
-		Form_pg_collation collform;
+		Datum		datum;
+		bool		isnull;
 		const char *collcollate;
 		const char *collctype;
 
 		tp = SearchSysCache1(COLLOID, ObjectIdGetDatum(collation));
 		if (!HeapTupleIsValid(tp))
 			elog(ERROR, "cache lookup failed for collation %u", collation);
-		collform = (Form_pg_collation) GETSTRUCT(tp);
 
-		collcollate = NameStr(collform->collcollate);
-		collctype = NameStr(collform->collctype);
+		datum = SysCacheGetAttr(COLLOID, tp, Anum_pg_collation_collcollate, &isnull);
+		Assert(!isnull);
+		collcollate = TextDatumGetCString(datum);
+		datum = SysCacheGetAttr(COLLOID, tp, Anum_pg_collation_collctype, &isnull);
+		Assert(!isnull);
+		collctype = TextDatumGetCString(datum);
 
 		cache_entry->collate_is_c = ((strcmp(collcollate, "C") == 0) ||
 									 (strcmp(collcollate, "POSIX") == 0));
@@ -1484,7 +1488,7 @@ pg_newlocale_from_collation(Oid collid)
 		const char *collctype pg_attribute_unused();
 		struct pg_locale_struct result;
 		pg_locale_t resultp;
-		Datum		collversion;
+		Datum		datum;
 		bool		isnull;
 
 		tp = SearchSysCache1(COLLOID, ObjectIdGetDatum(collid));
@@ -1492,8 +1496,12 @@ pg_newlocale_from_collation(Oid collid)
 			elog(ERROR, "cache lookup failed for collation %u", collid);
 		collform = (Form_pg_collation) GETSTRUCT(tp);
 
-		collcollate = NameStr(collform->collcollate);
-		collctype = NameStr(collform->collctype);
+		datum = SysCacheGetAttr(COLLOID, tp, Anum_pg_collation_collcollate, &isnull);
+		Assert(!isnull);
+		collcollate = TextDatumGetCString(datum);
+		datum = SysCacheGetAttr(COLLOID, tp, Anum_pg_collation_collctype, &isnull);
+		Assert(!isnull);
+		collctype = TextDatumGetCString(datum);
 
 		/* We'll fill in the result struct locally before allocating memory */
 		memset(&result, 0, sizeof(result));
@@ -1587,13 +1595,15 @@ pg_newlocale_from_collation(Oid collid)
 #endif							/* not USE_ICU */
 		}
 
-		collversion = SysCacheGetAttr(COLLOID, tp, Anum_pg_collation_collversion,
+		datum = SysCacheGetAttr(COLLOID, tp, Anum_pg_collation_collversion,
 									  &isnull);
 		if (!isnull)
 		{
 			char	   *actual_versionstr;
 			char	   *collversionstr;
 
+			collversionstr = TextDatumGetCString(datum);
+
 			actual_versionstr = get_collation_actual_version(collform->collprovider, collcollate);
 			if (!actual_versionstr)
 			{
@@ -1606,7 +1616,6 @@ pg_newlocale_from_collation(Oid collid)
 						(errmsg("collation \"%s\" has no actual version, but a version was specified",
 								NameStr(collform->collname))));
 			}
-			collversionstr = TextDatumGetCString(collversion);
 
 			if (strcmp(actual_versionstr, collversionstr) != 0)
 				ereport(WARNING,
diff --git a/src/backend/utils/init/postinit.c b/src/backend/utils/init/postinit.c
index 0236165f60..d046caabd7 100644
--- a/src/backend/utils/init/postinit.c
+++ b/src/backend/utils/init/postinit.c
@@ -53,6 +53,7 @@
 #include "storage/sync.h"
 #include "tcop/tcopprot.h"
 #include "utils/acl.h"
+#include "utils/builtins.h"
 #include "utils/fmgroids.h"
 #include "utils/guc.h"
 #include "utils/memutils.h"
@@ -306,6 +307,8 @@ CheckMyDatabase(const char *name, bool am_superuser, bool override_allow_connect
 {
 	HeapTuple	tup;
 	Form_pg_database dbform;
+	Datum		datum;
+	bool		isnull;
 	char	   *collate;
 	char	   *ctype;
 
@@ -389,8 +392,12 @@ CheckMyDatabase(const char *name, bool am_superuser, bool override_allow_connect
 					PGC_BACKEND, PGC_S_DYNAMIC_DEFAULT);
 
 	/* assign locale variables */
-	collate = NameStr(dbform->datcollate);
-	ctype = NameStr(dbform->datctype);
+	datum = SysCacheGetAttr(DATABASEOID, tup, Anum_pg_database_datcollate, &isnull);
+	Assert(!isnull);
+	collate = TextDatumGetCString(datum);
+	datum = SysCacheGetAttr(DATABASEOID, tup, Anum_pg_database_datctype, &isnull);
+	Assert(!isnull);
+	ctype = TextDatumGetCString(datum);
 
 	if (pg_perm_setlocale(LC_COLLATE, collate) == NULL)
 		ereport(FATAL,
diff --git a/src/include/catalog/pg_collation.h b/src/include/catalog/pg_collation.h
index bc746537c1..8763dd4080 100644
--- a/src/include/catalog/pg_collation.h
+++ b/src/include/catalog/pg_collation.h
@@ -39,9 +39,9 @@ CATALOG(pg_collation,3456,CollationRelationId)
 	char		collprovider;	/* see constants below */
 	bool		collisdeterministic BKI_DEFAULT(t);
 	int32		collencoding;	/* encoding for this collation; -1 = "all" */
-	NameData	collcollate;	/* LC_COLLATE setting */
-	NameData	collctype;		/* LC_CTYPE setting */
 #ifdef CATALOG_VARLEN			/* variable-length fields start here */
+	text		collcollate BKI_FORCE_NOT_NULL;		/* LC_COLLATE setting */
+	text		collctype BKI_FORCE_NOT_NULL;		/* LC_CTYPE setting */
 	text		collversion BKI_DEFAULT(_null_);	/* provider-dependent
 													 * version of collation
 													 * data */
diff --git a/src/include/catalog/pg_database.h b/src/include/catalog/pg_database.h
index 1ff6d3e50c..90b43a4ecc 100644
--- a/src/include/catalog/pg_database.h
+++ b/src/include/catalog/pg_database.h
@@ -40,12 +40,6 @@ CATALOG(pg_database,1262,DatabaseRelationId) BKI_SHARED_RELATION BKI_ROWTYPE_OID
 	/* character encoding */
 	int32		encoding;
 
-	/* LC_COLLATE setting */
-	NameData	datcollate;
-
-	/* LC_CTYPE setting */
-	NameData	datctype;
-
 	/* allowed as CREATE DATABASE template? */
 	bool		datistemplate;
 
@@ -65,6 +59,12 @@ CATALOG(pg_database,1262,DatabaseRelationId) BKI_SHARED_RELATION BKI_ROWTYPE_OID
 	Oid			dattablespace BKI_LOOKUP(pg_tablespace);
 
 #ifdef CATALOG_VARLEN			/* variable-length fields start here */
+	/* LC_COLLATE setting */
+	text		datcollate BKI_FORCE_NOT_NULL;
+
+	/* LC_CTYPE setting */
+	text		datctype BKI_FORCE_NOT_NULL;
+
 	/* access permissions */
 	aclitem		datacl[1];
 #endif
diff --git a/src/include/utils/pg_locale.h b/src/include/utils/pg_locale.h
index b4a2765983..30e423af0e 100644
--- a/src/include/utils/pg_locale.h
+++ b/src/include/utils/pg_locale.h
@@ -34,6 +34,8 @@
 #endif
 #endif
 
+/* use for libc locale names */
+#define LOCALE_NAME_BUFLEN 128
 
 /* GUC settings */
 extern char *locale_messages;
-- 
2.34.1

From 4028980f6be3662c0302575ed92de77e941e5a9e Mon Sep 17 00:00:00 2001
From: Peter Eisentraut <peter@eisentraut.org>
Date: Wed, 2 Feb 2022 13:54:04 +0100
Subject: [PATCH v4] Add option to use ICU as global collation provider

This adds the option to use ICU as the default collation provider for
either the whole cluster or a database.  New options for initdb,
createdb, and CREATE DATABASE are used to select this.

Discussion: https://www.postgresql.org/message-id/flat/5e756dd6-0e91-d778-96fd-b1bcb06c161a%402ndquadrant.com
---
 doc/src/sgml/catalogs.sgml                    |   9 +
 doc/src/sgml/ref/create_database.sgml         |  16 ++
 doc/src/sgml/ref/createdb.sgml                |   9 +
 doc/src/sgml/ref/initdb.sgml                  |  23 ++
 src/backend/catalog/pg_collation.c            |  18 +-
 src/backend/commands/collationcmds.c          |  93 ++++---
 src/backend/commands/dbcommands.c             |  72 +++++-
 src/backend/utils/adt/pg_locale.c             | 242 +++++++++++-------
 src/backend/utils/init/postinit.c             |  26 ++
 src/bin/initdb/Makefile                       |   2 +
 src/bin/initdb/initdb.c                       |  64 ++++-
 src/bin/initdb/t/001_initdb.pl                |  18 +-
 src/bin/pg_dump/pg_dump.c                     |  19 ++
 src/bin/pg_upgrade/check.c                    |  10 +
 src/bin/pg_upgrade/info.c                     |  18 +-
 src/bin/pg_upgrade/pg_upgrade.h               |   2 +
 src/bin/psql/describe.c                       |  23 +-
 src/bin/psql/tab-complete.c                   |   2 +-
 src/bin/scripts/Makefile                      |   2 +
 src/bin/scripts/createdb.c                    |   9 +
 src/bin/scripts/t/020_createdb.pl             |  20 +-
 src/include/catalog/pg_collation.dat          |   3 +-
 src/include/catalog/pg_collation.h            |   6 +-
 src/include/catalog/pg_database.dat           |   4 +-
 src/include/catalog/pg_database.h             |   6 +
 src/include/utils/pg_locale.h                 |   6 +
 .../regress/expected/collate.icu.utf8.out     |  10 +-
 src/test/regress/sql/collate.icu.utf8.sql     |   8 +-
 28 files changed, 572 insertions(+), 168 deletions(-)

diff --git a/doc/src/sgml/catalogs.sgml b/doc/src/sgml/catalogs.sgml
index 7d5b0b1656..5a5779b9a3 100644
--- a/doc/src/sgml/catalogs.sgml
+++ b/doc/src/sgml/catalogs.sgml
@@ -2384,6 +2384,15 @@ <title><structname>pg_collation</structname> Columns</title>
       </para></entry>
      </row>
 
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
+       <structfield>collicucoll</structfield> <type>text</type>
+      </para>
+      <para>
+       ICU collation string
+      </para></entry>
+     </row>
+
      <row>
       <entry role="catalog_table_entry"><para role="column_definition">
        <structfield>collversion</structfield> <type>text</type>
diff --git a/doc/src/sgml/ref/create_database.sgml b/doc/src/sgml/ref/create_database.sgml
index f22e28dc81..403010cddf 100644
--- a/doc/src/sgml/ref/create_database.sgml
+++ b/doc/src/sgml/ref/create_database.sgml
@@ -28,6 +28,7 @@
            [ LOCALE [=] <replaceable class="parameter">locale</replaceable> ]
            [ LC_COLLATE [=] <replaceable class="parameter">lc_collate</replaceable> ]
            [ LC_CTYPE [=] <replaceable class="parameter">lc_ctype</replaceable> ]
+           [ COLLATION_PROVIDER [=] <replaceable class="parameter">collation_provider</replaceable> ]
            [ TABLESPACE [=] <replaceable class="parameter">tablespace_name</replaceable> ]
            [ ALLOW_CONNECTIONS [=] <replaceable class="parameter">allowconn</replaceable> ]
            [ CONNECTION LIMIT [=] <replaceable class="parameter">connlimit</replaceable> ]
@@ -158,6 +159,21 @@ <title>Parameters</title>
        </para>
       </listitem>
      </varlistentry>
+
+     <varlistentry>
+      <term><replaceable>collation_provider</replaceable></term>
+
+      <listitem>
+       <para>
+        Specifies the provider to use for the default collation in this
+        database.  Possible values are:
+        <literal>icu</literal>,<indexterm><primary>ICU</primary></indexterm>
+        <literal>libc</literal>.  <literal>libc</literal> is the default.  The
+        available choices depend on the operating system and build options.
+       </para>
+      </listitem>
+     </varlistentry>
+
      <varlistentry>
       <term><replaceable class="parameter">tablespace_name</replaceable></term>
       <listitem>
diff --git a/doc/src/sgml/ref/createdb.sgml b/doc/src/sgml/ref/createdb.sgml
index 86473455c9..4b07363fcc 100644
--- a/doc/src/sgml/ref/createdb.sgml
+++ b/doc/src/sgml/ref/createdb.sgml
@@ -83,6 +83,15 @@ <title>Options</title>
       </listitem>
      </varlistentry>
 
+     <varlistentry>
+      <term><option>--collation-provider={<literal>libc</literal>|<literal>icu</literal>}</option></term>
+      <listitem>
+       <para>
+        Specifies the collation provider for the database's default collation.
+       </para>
+      </listitem>
+     </varlistentry>
+
      <varlistentry>
       <term><option>-D <replaceable class="parameter">tablespace</replaceable></option></term>
       <term><option>--tablespace=<replaceable class="parameter">tablespace</replaceable></option></term>
diff --git a/doc/src/sgml/ref/initdb.sgml b/doc/src/sgml/ref/initdb.sgml
index 8f71c7c962..77618d9a7a 100644
--- a/doc/src/sgml/ref/initdb.sgml
+++ b/doc/src/sgml/ref/initdb.sgml
@@ -166,6 +166,18 @@ <title>Options</title>
       </listitem>
      </varlistentry>
 
+     <varlistentry>
+      <term><option>--collation-provider={<literal>libc</literal>|<literal>icu</literal>}</option></term>
+      <listitem>
+       <para>
+        This option sets the collation provider for databases created in the
+        new cluster.  It can be overridden in the <command>CREATE
+        DATABASE</command> command when new databases are subsequently
+        created.  The default is <literal>libc</literal>.
+       </para>
+      </listitem>
+     </varlistentry>
+
      <varlistentry>
       <term><option>-D <replaceable class="parameter">directory</replaceable></option></term>
       <term><option>--pgdata=<replaceable class="parameter">directory</replaceable></option></term>
@@ -210,6 +222,17 @@ <title>Options</title>
       </listitem>
      </varlistentry>
 
+     <varlistentry>
+      <term><option>--icu-locale=<replaceable>locale</replaceable></option></term>
+      <listitem>
+       <para>
+        Specifies the ICU locale if the ICU collation provider is used.  If
+        this is not specified, the value from the <option>--locale</option>
+        option is used.
+       </para>
+      </listitem>
+     </varlistentry>
+
      <varlistentry id="app-initdb-data-checksums" xreflabel="data checksums">
       <term><option>-k</option></term>
       <term><option>--data-checksums</option></term>
diff --git a/src/backend/catalog/pg_collation.c b/src/backend/catalog/pg_collation.c
index bfc02d3038..5596b9be5a 100644
--- a/src/backend/catalog/pg_collation.c
+++ b/src/backend/catalog/pg_collation.c
@@ -49,6 +49,7 @@ CollationCreate(const char *collname, Oid collnamespace,
 				bool collisdeterministic,
 				int32 collencoding,
 				const char *collcollate, const char *collctype,
+				const char *collicucoll,
 				const char *collversion,
 				bool if_not_exists,
 				bool quiet)
@@ -66,8 +67,7 @@ CollationCreate(const char *collname, Oid collnamespace,
 	AssertArg(collname);
 	AssertArg(collnamespace);
 	AssertArg(collowner);
-	AssertArg(collcollate);
-	AssertArg(collctype);
+	AssertArg((collcollate && collctype) || collicucoll);
 
 	/*
 	 * Make sure there is no existing collation of same name & encoding.
@@ -161,8 +161,18 @@ CollationCreate(const char *collname, Oid collnamespace,
 	values[Anum_pg_collation_collprovider - 1] = CharGetDatum(collprovider);
 	values[Anum_pg_collation_collisdeterministic - 1] = BoolGetDatum(collisdeterministic);
 	values[Anum_pg_collation_collencoding - 1] = Int32GetDatum(collencoding);
-	values[Anum_pg_collation_collcollate - 1] = CStringGetTextDatum(collcollate);
-	values[Anum_pg_collation_collctype - 1] = CStringGetTextDatum(collctype);
+	if (collcollate)
+		values[Anum_pg_collation_collcollate - 1] = CStringGetTextDatum(collcollate);
+	else
+		nulls[Anum_pg_collation_collcollate - 1] = true;
+	if (collctype)
+		values[Anum_pg_collation_collctype - 1] = CStringGetTextDatum(collctype);
+	else
+		nulls[Anum_pg_collation_collctype - 1] = true;
+	if (collicucoll)
+		values[Anum_pg_collation_collicucoll - 1] = CStringGetTextDatum(collicucoll);
+	else
+		nulls[Anum_pg_collation_collicucoll - 1] = true;
 	if (collversion)
 		values[Anum_pg_collation_collversion - 1] = CStringGetTextDatum(collversion);
 	else
diff --git a/src/backend/commands/collationcmds.c b/src/backend/commands/collationcmds.c
index 12fc2316f9..a9b50f5d2b 100644
--- a/src/backend/commands/collationcmds.c
+++ b/src/backend/commands/collationcmds.c
@@ -65,6 +65,7 @@ DefineCollation(ParseState *pstate, List *names, List *parameters, bool if_not_e
 	DefElem    *versionEl = NULL;
 	char	   *collcollate = NULL;
 	char	   *collctype = NULL;
+	char	   *collicucoll = NULL;
 	char	   *collproviderstr = NULL;
 	bool		collisdeterministic = true;
 	int			collencoding = 0;
@@ -153,6 +154,12 @@ DefineCollation(ParseState *pstate, List *names, List *parameters, bool if_not_e
 		else
 			collctype = NULL;
 
+		datum = SysCacheGetAttr(COLLOID, tp, Anum_pg_collation_collicucoll, &isnull);
+		if (!isnull)
+			collicucoll = TextDatumGetCString(datum);
+		else
+			collicucoll = NULL;
+
 		ReleaseSysCache(tp);
 
 		/*
@@ -168,18 +175,6 @@ DefineCollation(ParseState *pstate, List *names, List *parameters, bool if_not_e
 					 errmsg("collation \"default\" cannot be copied")));
 	}
 
-	if (localeEl)
-	{
-		collcollate = defGetString(localeEl);
-		collctype = defGetString(localeEl);
-	}
-
-	if (lccollateEl)
-		collcollate = defGetString(lccollateEl);
-
-	if (lcctypeEl)
-		collctype = defGetString(lcctypeEl);
-
 	if (providerEl)
 		collproviderstr = defGetString(providerEl);
 
@@ -204,15 +199,43 @@ DefineCollation(ParseState *pstate, List *names, List *parameters, bool if_not_e
 	else if (!fromEl)
 		collprovider = COLLPROVIDER_LIBC;
 
-	if (!collcollate)
-		ereport(ERROR,
-				(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
-				 errmsg("parameter \"lc_collate\" must be specified")));
+	if (localeEl)
+	{
+		if (collprovider == COLLPROVIDER_LIBC)
+		{
+			collcollate = defGetString(localeEl);
+			collctype = defGetString(localeEl);
+		}
+		else
+			collicucoll = defGetString(localeEl);
+	}
 
-	if (!collctype)
-		ereport(ERROR,
-				(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
-				 errmsg("parameter \"lc_ctype\" must be specified")));
+	if (lccollateEl)
+		collcollate = defGetString(lccollateEl);
+
+	if (lcctypeEl)
+		collctype = defGetString(lcctypeEl);
+
+	if (collprovider == COLLPROVIDER_LIBC)
+	{
+		if (!collcollate)
+			ereport(ERROR,
+					(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
+					 errmsg("parameter \"lc_collate\" must be specified")));
+
+		if (!collctype)
+			ereport(ERROR,
+					(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
+					 errmsg("parameter \"lc_ctype\" must be specified")));
+	}
+
+	if (collprovider == COLLPROVIDER_ICU)
+	{
+		if (!collicucoll)
+			ereport(ERROR,
+					(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
+					 errmsg("parameter \"locale\" must be specified")));
+	}
 
 	/*
 	 * Nondeterministic collations are currently only supported with ICU
@@ -255,7 +278,7 @@ DefineCollation(ParseState *pstate, List *names, List *parameters, bool if_not_e
 	}
 
 	if (!collversion)
-		collversion = get_collation_actual_version(collprovider, collcollate);
+		collversion = get_collation_actual_version(collprovider, collprovider == COLLPROVIDER_ICU ? collicucoll : collcollate);
 
 	newoid = CollationCreate(collName,
 							 collNamespace,
@@ -265,6 +288,7 @@ DefineCollation(ParseState *pstate, List *names, List *parameters, bool if_not_e
 							 collencoding,
 							 collcollate,
 							 collctype,
+							 collicucoll,
 							 collversion,
 							 if_not_exists,
 							 false);	/* not quiet */
@@ -347,7 +371,7 @@ AlterCollation(AlterCollationStmt *stmt)
 	datum = SysCacheGetAttr(COLLOID, tup, Anum_pg_collation_collversion, &isnull);
 	oldversion = isnull ? NULL : TextDatumGetCString(datum);
 
-	datum = SysCacheGetAttr(COLLOID, tup, Anum_pg_collation_collcollate, &isnull);
+	datum = SysCacheGetAttr(COLLOID, tup, collForm->collprovider == COLLPROVIDER_ICU ? Anum_pg_collation_collicucoll : Anum_pg_collation_collcollate, &isnull);
 	Assert(!isnull);
 	newversion = get_collation_actual_version(collForm->collprovider, TextDatumGetCString(datum));
 
@@ -409,9 +433,14 @@ pg_collation_actual_version(PG_FUNCTION_ARGS)
 
 	collprovider = ((Form_pg_collation) GETSTRUCT(tp))->collprovider;
 
-	datum = SysCacheGetAttr(COLLOID, tp, Anum_pg_collation_collcollate, &isnull);
-	Assert(!isnull);
-	version = get_collation_actual_version(collprovider, TextDatumGetCString(datum));
+	if (collprovider != COLLPROVIDER_DEFAULT)
+	{
+		datum = SysCacheGetAttr(COLLOID, tp, collprovider == COLLPROVIDER_ICU ? Anum_pg_collation_collicucoll : Anum_pg_collation_collcollate, &isnull);
+		Assert(!isnull);
+		version = get_collation_actual_version(collprovider, TextDatumGetCString(datum));
+	}
+	else
+		version = NULL;
 
 	ReleaseSysCache(tp);
 
@@ -638,7 +667,7 @@ pg_import_system_collations(PG_FUNCTION_ARGS)
 			 */
 			collid = CollationCreate(localebuf, nspid, GetUserId(),
 									 COLLPROVIDER_LIBC, true, enc,
-									 localebuf, localebuf,
+									 localebuf, localebuf, NULL,
 									 get_collation_actual_version(COLLPROVIDER_LIBC, localebuf),
 									 true, true);
 			if (OidIsValid(collid))
@@ -699,7 +728,7 @@ pg_import_system_collations(PG_FUNCTION_ARGS)
 
 			collid = CollationCreate(alias, nspid, GetUserId(),
 									 COLLPROVIDER_LIBC, true, enc,
-									 locale, locale,
+									 locale, locale, NULL,
 									 get_collation_actual_version(COLLPROVIDER_LIBC, locale),
 									 true, true);
 			if (OidIsValid(collid))
@@ -740,7 +769,7 @@ pg_import_system_collations(PG_FUNCTION_ARGS)
 			const char *name;
 			char	   *langtag;
 			char	   *icucomment;
-			const char *collcollate;
+			const char *icucollstr;
 			Oid			collid;
 
 			if (i == -1)
@@ -749,20 +778,20 @@ pg_import_system_collations(PG_FUNCTION_ARGS)
 				name = uloc_getAvailable(i);
 
 			langtag = get_icu_language_tag(name);
-			collcollate = U_ICU_VERSION_MAJOR_NUM >= 54 ? langtag : name;
+			icucollstr = U_ICU_VERSION_MAJOR_NUM >= 54 ? langtag : name;
 
 			/*
 			 * Be paranoid about not allowing any non-ASCII strings into
 			 * pg_collation
 			 */
-			if (!pg_is_ascii(langtag) || !pg_is_ascii(collcollate))
+			if (!pg_is_ascii(langtag) || !pg_is_ascii(icucollstr))
 				continue;
 
 			collid = CollationCreate(psprintf("%s-x-icu", langtag),
 									 nspid, GetUserId(),
 									 COLLPROVIDER_ICU, true, -1,
-									 collcollate, collcollate,
-									 get_collation_actual_version(COLLPROVIDER_ICU, collcollate),
+									 NULL, NULL, icucollstr,
+									 get_collation_actual_version(COLLPROVIDER_ICU, icucollstr),
 									 true, true);
 			if (OidIsValid(collid))
 			{
diff --git a/src/backend/commands/dbcommands.c b/src/backend/commands/dbcommands.c
index e673138cbd..df7087cd7b 100644
--- a/src/backend/commands/dbcommands.c
+++ b/src/backend/commands/dbcommands.c
@@ -36,6 +36,7 @@
 #include "catalog/indexing.h"
 #include "catalog/objectaccess.h"
 #include "catalog/pg_authid.h"
+#include "catalog/pg_collation.h"
 #include "catalog/pg_database.h"
 #include "catalog/pg_db_role_setting.h"
 #include "catalog/pg_subscription.h"
@@ -85,7 +86,8 @@ static bool get_db_info(const char *name, LOCKMODE lockmode,
 						Oid *dbIdP, Oid *ownerIdP,
 						int *encodingP, bool *dbIsTemplateP, bool *dbAllowConnP,
 						TransactionId *dbFrozenXidP, MultiXactId *dbMinMultiP,
-						Oid *dbTablespace, char **dbCollate, char **dbCtype);
+						Oid *dbTablespace, char **dbCollate, char **dbCtype, char **dbIcucoll,
+						char *dbCollProvider);
 static bool have_createdb_privilege(void);
 static void remove_dbtablespaces(Oid db_id);
 static bool check_db_file_conflict(Oid db_id);
@@ -105,6 +107,8 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 	int			src_encoding = -1;
 	char	   *src_collate = NULL;
 	char	   *src_ctype = NULL;
+	char	   *src_icucoll = NULL;
+	char		src_collprovider;
 	bool		src_istemplate;
 	bool		src_allowconn;
 	TransactionId src_frozenxid = InvalidTransactionId;
@@ -125,6 +129,7 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 	DefElem    *dlocale = NULL;
 	DefElem    *dcollate = NULL;
 	DefElem    *dctype = NULL;
+	DefElem	   *dcollprovider = NULL;
 	DefElem    *distemplate = NULL;
 	DefElem    *dallowconnections = NULL;
 	DefElem    *dconnlimit = NULL;
@@ -133,6 +138,8 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 	const char *dbtemplate = NULL;
 	char	   *dbcollate = NULL;
 	char	   *dbctype = NULL;
+	char	   *dbicucoll = NULL;
+	char		dbcollprovider = '\0';
 	char	   *canonname;
 	int			encoding = -1;
 	bool		dbistemplate = false;
@@ -189,6 +196,15 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 				errorConflictingDefElem(defel, pstate);
 			dctype = defel;
 		}
+		else if (strcmp(defel->defname, "collation_provider") == 0)
+		{
+			if (dcollprovider)
+				ereport(ERROR,
+						(errcode(ERRCODE_SYNTAX_ERROR),
+						 errmsg("conflicting or redundant options"),
+						 parser_errposition(pstate, defel->location)));
+			dcollprovider = defel;
+		}
 		else if (strcmp(defel->defname, "is_template") == 0)
 		{
 			if (distemplate)
@@ -246,12 +262,6 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 					 parser_errposition(pstate, defel->location)));
 	}
 
-	if (dlocale && (dcollate || dctype))
-		ereport(ERROR,
-				(errcode(ERRCODE_SYNTAX_ERROR),
-				 errmsg("conflicting or redundant options"),
-				 errdetail("LOCALE cannot be specified together with LC_COLLATE or LC_CTYPE.")));
-
 	if (downer && downer->arg)
 		dbowner = defGetString(downer);
 	if (dtemplate && dtemplate->arg)
@@ -288,11 +298,29 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 	{
 		dbcollate = defGetString(dlocale);
 		dbctype = defGetString(dlocale);
+		dbicucoll = defGetString(dlocale);
 	}
 	if (dcollate && dcollate->arg)
 		dbcollate = defGetString(dcollate);
 	if (dctype && dctype->arg)
 		dbctype = defGetString(dctype);
+	if (dcollprovider && dcollprovider->arg)
+	{
+		char	   *collproviderstr = defGetString(dcollprovider);
+
+#ifdef USE_ICU
+		if (pg_strcasecmp(collproviderstr, "icu") == 0)
+			dbcollprovider = COLLPROVIDER_ICU;
+		else
+#endif
+		if (pg_strcasecmp(collproviderstr, "libc") == 0)
+			dbcollprovider = COLLPROVIDER_LIBC;
+		else
+			ereport(ERROR,
+					(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
+					 errmsg("unrecognized collation provider: %s",
+							collproviderstr)));
+	}
 	if (distemplate && distemplate->arg)
 		dbistemplate = defGetBoolean(distemplate);
 	if (dallowconnections && dallowconnections->arg)
@@ -342,7 +370,7 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 					 &src_dboid, &src_owner, &src_encoding,
 					 &src_istemplate, &src_allowconn,
 					 &src_frozenxid, &src_minmxid, &src_deftablespace,
-					 &src_collate, &src_ctype))
+					 &src_collate, &src_ctype, &src_icucoll, &src_collprovider))
 		ereport(ERROR,
 				(errcode(ERRCODE_UNDEFINED_DATABASE),
 				 errmsg("template database \"%s\" does not exist",
@@ -368,6 +396,10 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 		dbcollate = src_collate;
 	if (dbctype == NULL)
 		dbctype = src_ctype;
+	if (dbicucoll == NULL)
+		dbicucoll = src_icucoll;
+	if (dbcollprovider == '\0')
+		dbcollprovider = src_collprovider;
 
 	/* Some encodings are client only */
 	if (!PG_VALID_BE_ENCODING(encoding))
@@ -570,6 +602,7 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 		DirectFunctionCall1(namein, CStringGetDatum(dbname));
 	new_record[Anum_pg_database_datdba - 1] = ObjectIdGetDatum(datdba);
 	new_record[Anum_pg_database_encoding - 1] = Int32GetDatum(encoding);
+	new_record[Anum_pg_database_datcollprovider - 1] = CharGetDatum(dbcollprovider);
 	new_record[Anum_pg_database_datistemplate - 1] = BoolGetDatum(dbistemplate);
 	new_record[Anum_pg_database_datallowconn - 1] = BoolGetDatum(dballowconnections);
 	new_record[Anum_pg_database_datconnlimit - 1] = Int32GetDatum(dbconnlimit);
@@ -578,6 +611,10 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 	new_record[Anum_pg_database_dattablespace - 1] = ObjectIdGetDatum(dst_deftablespace);
 	new_record[Anum_pg_database_datcollate - 1] = CStringGetTextDatum(dbcollate);
 	new_record[Anum_pg_database_datctype - 1] = CStringGetTextDatum(dbctype);
+	if (dbicucoll)
+		new_record[Anum_pg_database_daticucoll - 1] = CStringGetTextDatum(dbicucoll);
+	else
+		new_record_nulls[Anum_pg_database_daticucoll] = true;
 
 	/*
 	 * We deliberately set datacl to default (NULL), rather than copying it
@@ -844,7 +881,7 @@ dropdb(const char *dbname, bool missing_ok, bool force)
 	pgdbrel = table_open(DatabaseRelationId, RowExclusiveLock);
 
 	if (!get_db_info(dbname, AccessExclusiveLock, &db_id, NULL, NULL,
-					 &db_istemplate, NULL, NULL, NULL, NULL, NULL, NULL))
+					 &db_istemplate, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL))
 	{
 		if (!missing_ok)
 		{
@@ -1043,7 +1080,7 @@ RenameDatabase(const char *oldname, const char *newname)
 	rel = table_open(DatabaseRelationId, RowExclusiveLock);
 
 	if (!get_db_info(oldname, AccessExclusiveLock, &db_id, NULL, NULL,
-					 NULL, NULL, NULL, NULL, NULL, NULL, NULL))
+					 NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL))
 		ereport(ERROR,
 				(errcode(ERRCODE_UNDEFINED_DATABASE),
 				 errmsg("database \"%s\" does not exist", oldname)));
@@ -1156,7 +1193,7 @@ movedb(const char *dbname, const char *tblspcname)
 	pgdbrel = table_open(DatabaseRelationId, RowExclusiveLock);
 
 	if (!get_db_info(dbname, AccessExclusiveLock, &db_id, NULL, NULL,
-					 NULL, NULL, NULL, NULL, &src_tblspcoid, NULL, NULL))
+					 NULL, NULL, NULL, NULL, &src_tblspcoid, NULL, NULL, NULL, NULL))
 		ereport(ERROR,
 				(errcode(ERRCODE_UNDEFINED_DATABASE),
 				 errmsg("database \"%s\" does not exist", dbname)));
@@ -1800,7 +1837,8 @@ get_db_info(const char *name, LOCKMODE lockmode,
 			Oid *dbIdP, Oid *ownerIdP,
 			int *encodingP, bool *dbIsTemplateP, bool *dbAllowConnP,
 			TransactionId *dbFrozenXidP, MultiXactId *dbMinMultiP,
-			Oid *dbTablespace, char **dbCollate, char **dbCtype)
+			Oid *dbTablespace, char **dbCollate, char **dbCtype, char **dbIcucoll,
+			char *dbCollProvider)
 {
 	bool		result = false;
 	Relation	relation;
@@ -1893,6 +1931,8 @@ get_db_info(const char *name, LOCKMODE lockmode,
 				if (dbTablespace)
 					*dbTablespace = dbform->dattablespace;
 				/* default locale settings for this database */
+				if (dbCollProvider)
+					*dbCollProvider = dbform->datcollprovider;
 				if (dbCollate)
 				{
 					datum = SysCacheGetAttr(DATABASEOID, tuple, Anum_pg_database_datcollate, &isnull);
@@ -1905,6 +1945,14 @@ get_db_info(const char *name, LOCKMODE lockmode,
 					Assert(!isnull);
 					*dbCtype = TextDatumGetCString(datum);
 				}
+				if (dbIcucoll)
+				{
+					datum = SysCacheGetAttr(DATABASEOID, tuple, Anum_pg_database_daticucoll, &isnull);
+					if (isnull)
+						*dbIcucoll = NULL;
+					else
+						*dbIcucoll = TextDatumGetCString(datum);
+				}
 				ReleaseSysCache(tuple);
 				result = true;
 				break;
diff --git a/src/backend/utils/adt/pg_locale.c b/src/backend/utils/adt/pg_locale.c
index aefa0818d0..0334f66a23 100644
--- a/src/backend/utils/adt/pg_locale.c
+++ b/src/backend/utils/adt/pg_locale.c
@@ -1288,26 +1288,37 @@ lookup_collation_cache(Oid collation, bool set_flags)
 	{
 		/* Attempt to set the flags */
 		HeapTuple	tp;
-		Datum		datum;
-		bool		isnull;
-		const char *collcollate;
-		const char *collctype;
+		Form_pg_collation collform;
 
 		tp = SearchSysCache1(COLLOID, ObjectIdGetDatum(collation));
 		if (!HeapTupleIsValid(tp))
 			elog(ERROR, "cache lookup failed for collation %u", collation);
+		collform = (Form_pg_collation) GETSTRUCT(tp);
 
-		datum = SysCacheGetAttr(COLLOID, tp, Anum_pg_collation_collcollate, &isnull);
-		Assert(!isnull);
-		collcollate = TextDatumGetCString(datum);
-		datum = SysCacheGetAttr(COLLOID, tp, Anum_pg_collation_collctype, &isnull);
-		Assert(!isnull);
-		collctype = TextDatumGetCString(datum);
-
-		cache_entry->collate_is_c = ((strcmp(collcollate, "C") == 0) ||
-									 (strcmp(collcollate, "POSIX") == 0));
-		cache_entry->ctype_is_c = ((strcmp(collctype, "C") == 0) ||
-								   (strcmp(collctype, "POSIX") == 0));
+		if (collform->collprovider == COLLPROVIDER_LIBC)
+		{
+			Datum		datum;
+			bool		isnull;
+			const char *collcollate;
+			const char *collctype;
+
+			datum = SysCacheGetAttr(COLLOID, tp, Anum_pg_collation_collcollate, &isnull);
+			Assert(!isnull);
+			collcollate = TextDatumGetCString(datum);
+			datum = SysCacheGetAttr(COLLOID, tp, Anum_pg_collation_collctype, &isnull);
+			Assert(!isnull);
+			collctype = TextDatumGetCString(datum);
+
+			cache_entry->collate_is_c = ((strcmp(collcollate, "C") == 0) ||
+										 (strcmp(collcollate, "POSIX") == 0));
+			cache_entry->ctype_is_c = ((strcmp(collctype, "C") == 0) ||
+									   (strcmp(collctype, "POSIX") == 0));
+		}
+		else
+		{
+			cache_entry->collate_is_c = false;
+			cache_entry->ctype_is_c = false;
+		}
 
 		cache_entry->flags_valid = true;
 
@@ -1340,6 +1351,9 @@ lc_collate_is_c(Oid collation)
 		static int	result = -1;
 		char	   *localeptr;
 
+		if (default_locale.provider == COLLPROVIDER_ICU)
+			return false;
+
 		if (result >= 0)
 			return (bool) result;
 		localeptr = setlocale(LC_COLLATE, NULL);
@@ -1390,6 +1404,9 @@ lc_ctype_is_c(Oid collation)
 		static int	result = -1;
 		char	   *localeptr;
 
+		if (default_locale.provider == COLLPROVIDER_ICU)
+			return false;
+
 		if (result >= 0)
 			return (bool) result;
 		localeptr = setlocale(LC_CTYPE, NULL);
@@ -1418,6 +1435,87 @@ lc_ctype_is_c(Oid collation)
 	return (lookup_collation_cache(collation, true))->ctype_is_c;
 }
 
+struct pg_locale_struct default_locale;
+
+void
+make_icu_collator(const char *icucollstr,
+				  struct pg_locale_struct *resultp)
+{
+#ifdef USE_ICU
+	UCollator  *collator;
+	UErrorCode	status;
+
+	status = U_ZERO_ERROR;
+	collator = ucol_open(icucollstr, &status);
+	if (U_FAILURE(status))
+		ereport(ERROR,
+				(errmsg("could not open collator for locale \"%s\": %s",
+						icucollstr, u_errorName(status))));
+
+	if (U_ICU_VERSION_MAJOR_NUM < 54)
+		icu_set_collation_attributes(collator, icucollstr);
+
+	/* We will leak this string if we get an error below :-( */
+	resultp->info.icu.locale = MemoryContextStrdup(TopMemoryContext, icucollstr);
+	resultp->info.icu.ucol = collator;
+#else							/* not USE_ICU */
+	/* could get here if a collation was created by a build with ICU */
+	ereport(ERROR,
+			(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+			 errmsg("ICU is not supported in this build"), \
+			 errhint("You need to rebuild PostgreSQL using %s.", "--with-icu")));
+#endif							/* not USE_ICU */
+}
+
+void
+check_collation_version(HeapTuple colltuple)
+{
+	Form_pg_collation collform;
+	Datum		datum;
+	bool		isnull;
+
+	collform = (Form_pg_collation) GETSTRUCT(colltuple);
+
+	datum = SysCacheGetAttr(COLLOID, colltuple, Anum_pg_collation_collversion,
+							&isnull);
+	if (!isnull)
+	{
+		char	   *actual_versionstr;
+		char	   *collversionstr;
+
+		collversionstr = TextDatumGetCString(datum);
+
+		datum = SysCacheGetAttr(COLLOID, colltuple, collform->collprovider == COLLPROVIDER_ICU ? Anum_pg_collation_collicucoll : Anum_pg_collation_collcollate, &isnull);
+		Assert(!isnull);
+
+		actual_versionstr = get_collation_actual_version(collform->collprovider,
+														 TextDatumGetCString(datum));
+		if (!actual_versionstr)
+		{
+			/*
+			 * This could happen when specifying a version in CREATE
+			 * COLLATION for a libc locale, or manually creating a mess in
+			 * the catalogs.
+			 */
+			ereport(ERROR,
+					(errmsg("collation \"%s\" has no actual version, but a version was specified",
+							NameStr(collform->collname))));
+		}
+
+		if (strcmp(actual_versionstr, collversionstr) != 0)
+			ereport(WARNING,
+					(errmsg("collation \"%s\" has version mismatch",
+							NameStr(collform->collname)),
+					 errdetail("The collation in the database was created using version %s, "
+							   "but the operating system provides version %s.",
+							   collversionstr, actual_versionstr),
+					 errhint("Rebuild all objects affected by this collation and run "
+							 "ALTER COLLATION %s REFRESH VERSION, "
+							 "or build PostgreSQL with the right library version.",
+							 quote_qualified_identifier(get_namespace_name(collform->collnamespace),
+														NameStr(collform->collname)))));
+	}
+}
 
 /* simple subroutine for reporting errors from newlocale() */
 #ifdef HAVE_LOCALE_T
@@ -1475,7 +1573,12 @@ pg_newlocale_from_collation(Oid collid)
 	Assert(OidIsValid(collid));
 
 	if (collid == DEFAULT_COLLATION_OID)
-		return (pg_locale_t) 0;
+	{
+		if (default_locale.provider == COLLPROVIDER_ICU)
+			return &default_locale;
+		else
+			return (pg_locale_t) 0;
+	}
 
 	cache_entry = lookup_collation_cache(collid, false);
 
@@ -1484,25 +1587,14 @@ pg_newlocale_from_collation(Oid collid)
 		/* We haven't computed this yet in this session, so do it */
 		HeapTuple	tp;
 		Form_pg_collation collform;
-		const char *collcollate;
-		const char *collctype pg_attribute_unused();
 		struct pg_locale_struct result;
 		pg_locale_t resultp;
-		Datum		datum;
-		bool		isnull;
 
 		tp = SearchSysCache1(COLLOID, ObjectIdGetDatum(collid));
 		if (!HeapTupleIsValid(tp))
 			elog(ERROR, "cache lookup failed for collation %u", collid);
 		collform = (Form_pg_collation) GETSTRUCT(tp);
 
-		datum = SysCacheGetAttr(COLLOID, tp, Anum_pg_collation_collcollate, &isnull);
-		Assert(!isnull);
-		collcollate = TextDatumGetCString(datum);
-		datum = SysCacheGetAttr(COLLOID, tp, Anum_pg_collation_collctype, &isnull);
-		Assert(!isnull);
-		collctype = TextDatumGetCString(datum);
-
 		/* We'll fill in the result struct locally before allocating memory */
 		memset(&result, 0, sizeof(result));
 		result.provider = collform->collprovider;
@@ -1511,8 +1603,19 @@ pg_newlocale_from_collation(Oid collid)
 		if (collform->collprovider == COLLPROVIDER_LIBC)
 		{
 #ifdef HAVE_LOCALE_T
+			Datum		datum;
+			bool		isnull;
+			const char *collcollate;
+			const char *collctype pg_attribute_unused();
 			locale_t	loc;
 
+			datum = SysCacheGetAttr(COLLOID, tp, Anum_pg_collation_collcollate, &isnull);
+			Assert(!isnull);
+			collcollate = TextDatumGetCString(datum);
+			datum = SysCacheGetAttr(COLLOID, tp, Anum_pg_collation_collctype, &isnull);
+			Assert(!isnull);
+			collctype = TextDatumGetCString(datum);
+
 			if (strcmp(collcollate, collctype) == 0)
 			{
 				/* Normal case where they're the same */
@@ -1563,73 +1666,17 @@ pg_newlocale_from_collation(Oid collid)
 		}
 		else if (collform->collprovider == COLLPROVIDER_ICU)
 		{
-#ifdef USE_ICU
-			UCollator  *collator;
-			UErrorCode	status;
-
-			if (strcmp(collcollate, collctype) != 0)
-				ereport(ERROR,
-						(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-						 errmsg("collations with different collate and ctype values are not supported by ICU")));
-
-			status = U_ZERO_ERROR;
-			collator = ucol_open(collcollate, &status);
-			if (U_FAILURE(status))
-				ereport(ERROR,
-						(errmsg("could not open collator for locale \"%s\": %s",
-								collcollate, u_errorName(status))));
-
-			if (U_ICU_VERSION_MAJOR_NUM < 54)
-				icu_set_collation_attributes(collator, collcollate);
-
-			/* We will leak this string if we get an error below :-( */
-			result.info.icu.locale = MemoryContextStrdup(TopMemoryContext,
-														 collcollate);
-			result.info.icu.ucol = collator;
-#else							/* not USE_ICU */
-			/* could get here if a collation was created by a build with ICU */
-			ereport(ERROR,
-					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-					 errmsg("ICU is not supported in this build"), \
-					 errhint("You need to rebuild PostgreSQL using %s.", "--with-icu")));
-#endif							/* not USE_ICU */
+			Datum		datum;
+			bool		isnull;
+			const char *icucollstr;;
+
+			datum = SysCacheGetAttr(COLLOID, tp, Anum_pg_collation_collicucoll, &isnull);
+			Assert(!isnull);
+			icucollstr = TextDatumGetCString(datum);
+			make_icu_collator(icucollstr, &result);
 		}
 
-		datum = SysCacheGetAttr(COLLOID, tp, Anum_pg_collation_collversion,
-									  &isnull);
-		if (!isnull)
-		{
-			char	   *actual_versionstr;
-			char	   *collversionstr;
-
-			collversionstr = TextDatumGetCString(datum);
-
-			actual_versionstr = get_collation_actual_version(collform->collprovider, collcollate);
-			if (!actual_versionstr)
-			{
-				/*
-				 * This could happen when specifying a version in CREATE
-				 * COLLATION for a libc locale, or manually creating a mess in
-				 * the catalogs.
-				 */
-				ereport(ERROR,
-						(errmsg("collation \"%s\" has no actual version, but a version was specified",
-								NameStr(collform->collname))));
-			}
-
-			if (strcmp(actual_versionstr, collversionstr) != 0)
-				ereport(WARNING,
-						(errmsg("collation \"%s\" has version mismatch",
-								NameStr(collform->collname)),
-						 errdetail("The collation in the database was created using version %s, "
-								   "but the operating system provides version %s.",
-								   collversionstr, actual_versionstr),
-						 errhint("Rebuild all objects affected by this collation and run "
-								 "ALTER COLLATION %s REFRESH VERSION, "
-								 "or build PostgreSQL with the right library version.",
-								 quote_qualified_identifier(get_namespace_name(collform->collnamespace),
-															NameStr(collform->collname)))));
-		}
+		check_collation_version(tp);
 
 		ReleaseSysCache(tp);
 
@@ -1652,6 +1699,17 @@ get_collation_actual_version(char collprovider, const char *collcollate)
 {
 	char	   *collversion = NULL;
 
+	if (collprovider == COLLPROVIDER_DEFAULT)
+	{
+#ifdef USE_ICU
+		if (default_locale.provider == COLLPROVIDER_ICU)
+			collversion = get_collation_actual_version(default_locale.provider,
+													   default_locale.info.icu.locale);
+		else
+#endif
+			collversion = NULL;
+	}
+	else
 #ifdef USE_ICU
 	if (collprovider == COLLPROVIDER_ICU)
 	{
diff --git a/src/backend/utils/init/postinit.c b/src/backend/utils/init/postinit.c
index 5b9ed2f6f5..ffe60673d5 100644
--- a/src/backend/utils/init/postinit.c
+++ b/src/backend/utils/init/postinit.c
@@ -31,6 +31,7 @@
 #include "catalog/catalog.h"
 #include "catalog/namespace.h"
 #include "catalog/pg_authid.h"
+#include "catalog/pg_collation.h"
 #include "catalog/pg_database.h"
 #include "catalog/pg_db_role_setting.h"
 #include "catalog/pg_tablespace.h"
@@ -414,6 +415,31 @@ CheckMyDatabase(const char *name, bool am_superuser, bool override_allow_connect
 						   " which is not recognized by setlocale().", ctype),
 				 errhint("Recreate the database with another locale or install the missing locale.")));
 
+	if (dbform->datcollprovider == COLLPROVIDER_ICU)
+	{
+		datum = SysCacheGetAttr(DATABASEOID, tup, Anum_pg_database_daticucoll, &isnull);
+		Assert(!isnull);
+		make_icu_collator(TextDatumGetCString(datum), &default_locale);
+	}
+
+	default_locale.provider = dbform->datcollprovider;
+	/*
+	 * Default locale is currently always deterministic.  Nondeterministic
+	 * locales currently don't support pattern matching, which would break a
+	 * lot of things if applied globally.
+	 */
+	default_locale.deterministic = true;
+
+	{
+		HeapTuple	tp;
+
+		tp = SearchSysCache1(COLLOID, ObjectIdGetDatum(DEFAULT_COLLATION_OID));
+		if (!HeapTupleIsValid(tp))
+			elog(ERROR, "cache lookup failed for collation %u", DEFAULT_COLLATION_OID);
+		check_collation_version(tp);
+		ReleaseSysCache(tp);
+	}
+
 	/* Make the locale settings visible as GUC variables, too */
 	SetConfigOption("lc_collate", collate, PGC_INTERNAL, PGC_S_OVERRIDE);
 	SetConfigOption("lc_ctype", ctype, PGC_INTERNAL, PGC_S_OVERRIDE);
diff --git a/src/bin/initdb/Makefile b/src/bin/initdb/Makefile
index eba282267a..b0dd13dfbd 100644
--- a/src/bin/initdb/Makefile
+++ b/src/bin/initdb/Makefile
@@ -62,6 +62,8 @@ clean distclean maintainer-clean:
 # ensure that changes in datadir propagate into object file
 initdb.o: initdb.c $(top_builddir)/src/Makefile.global
 
+export with_icu
+
 check:
 	$(prove_check)
 
diff --git a/src/bin/initdb/initdb.c b/src/bin/initdb/initdb.c
index d78e8e67b8..64880038ca 100644
--- a/src/bin/initdb/initdb.c
+++ b/src/bin/initdb/initdb.c
@@ -132,6 +132,8 @@ static char *lc_monetary = NULL;
 static char *lc_numeric = NULL;
 static char *lc_time = NULL;
 static char *lc_messages = NULL;
+static char collation_provider[] = {COLLPROVIDER_LIBC, '\0'};
+static char *icu_locale = NULL;
 static const char *default_text_search_config = NULL;
 static char *username = NULL;
 static bool pwprompt = false;
@@ -1405,6 +1407,12 @@ bootstrap_template1(void)
 	bki_lines = replace_token(bki_lines, "LC_CTYPE",
 							  escape_quotes_bki(lc_ctype));
 
+	bki_lines = replace_token(bki_lines, "ICUCOLL",
+							  escape_quotes_bki(collation_provider[0] == COLLPROVIDER_ICU ? icu_locale : "_null_"));
+
+	bki_lines = replace_token(bki_lines, "COLLPROVIDER",
+							  collation_provider);
+
 	/* Also ensure backend isn't confused by this environment var: */
 	unsetenv("PGCLIENTENCODING");
 
@@ -1587,6 +1595,12 @@ setup_description(FILE *cmdfd)
 static void
 setup_collation(FILE *cmdfd)
 {
+	/*
+	 * Set version of the default collation.
+	 */
+	PG_CMD_PRINTF("UPDATE pg_collation SET collversion = pg_collation_actual_version(oid) WHERE oid = %d;\n\n",
+				  DEFAULT_COLLATION_OID);
+
 	/*
 	 * Add an SQL-standard name.  We don't want to pin this, so it doesn't go
 	 * in pg_collation.h.  But add it before reading system collations, so
@@ -1854,9 +1868,6 @@ make_template0(FILE *cmdfd)
 	 * the new cluster should be the result of a fresh initdb.)
 	 */
 	static const char *const template0_setup[] = {
-		"CREATE DATABASE template0 IS_TEMPLATE = true ALLOW_CONNECTIONS = false OID = "
-		CppAsString2(Template0ObjectId) ";\n\n",
-
 		/*
 		 * Explicitly revoke public create-schema and create-temp-table
 		 * privileges in template1 and template0; else the latter would be on
@@ -1874,6 +1885,10 @@ make_template0(FILE *cmdfd)
 		NULL
 	};
 
+	PG_CMD_PRINTF("CREATE DATABASE template0 IS_TEMPLATE = true ALLOW_CONNECTIONS = false OID = "
+				  CppAsString2(Template0ObjectId) " COLLATION_PROVIDER = %s;\n\n",
+				  collation_provider[0] == COLLPROVIDER_ICU ? "icu" : "libc");
+
 	for (line = template0_setup; *line; line++)
 		PG_CMD_PUTS(*line);
 }
@@ -2147,13 +2162,14 @@ setlocales(void)
 			lc_monetary = locale;
 		if (!lc_messages)
 			lc_messages = locale;
+		if (!icu_locale)
+			icu_locale = locale;
 	}
 
 	/*
 	 * canonicalize locale names, and obtain any missing values from our
 	 * current environment
 	 */
-
 	check_locale_name(LC_CTYPE, lc_ctype, &canonname);
 	lc_ctype = canonname;
 	check_locale_name(LC_COLLATE, lc_collate, &canonname);
@@ -2172,6 +2188,18 @@ setlocales(void)
 	check_locale_name(LC_CTYPE, lc_messages, &canonname);
 	lc_messages = canonname;
 #endif
+
+	/*
+	 * If ICU is selected but no ICU locale has been given, take the
+	 * lc_collate locale and chop off any encoding suffix.  This should give
+	 * the user a configuration that resembles their operating system's locale
+	 * setup.
+	 */
+	if (collation_provider[0] == COLLPROVIDER_ICU && !icu_locale)
+	{
+		icu_locale = pg_strdup(lc_collate);
+		icu_locale[strcspn(icu_locale, ".")] = '\0';
+	}
 }
 
 /*
@@ -2187,9 +2215,12 @@ usage(const char *progname)
 	printf(_("  -A, --auth=METHOD         default authentication method for local connections\n"));
 	printf(_("      --auth-host=METHOD    default authentication method for local TCP/IP connections\n"));
 	printf(_("      --auth-local=METHOD   default authentication method for local-socket connections\n"));
+	printf(_("      --collation-provider={libc|icu}\n"
+			 "                            set default collation provider for new databases\n"));
 	printf(_(" [-D, --pgdata=]DATADIR     location for this database cluster\n"));
 	printf(_("  -E, --encoding=ENCODING   set default encoding for new databases\n"));
 	printf(_("  -g, --allow-group-access  allow group read/execute on data directory\n"));
+	printf(_("      --icu-locale          set ICU locale for new databases\n"));
 	printf(_("  -k, --data-checksums      use data page checksums\n"));
 	printf(_("      --locale=LOCALE       set default locale for new databases\n"));
 	printf(_("      --lc-collate=, --lc-ctype=, --lc-messages=LOCALE\n"
@@ -2364,7 +2395,8 @@ setup_locale_encoding(void)
 		strcmp(lc_ctype, lc_time) == 0 &&
 		strcmp(lc_ctype, lc_numeric) == 0 &&
 		strcmp(lc_ctype, lc_monetary) == 0 &&
-		strcmp(lc_ctype, lc_messages) == 0)
+		strcmp(lc_ctype, lc_messages) == 0 &&
+		(!icu_locale || strcmp(lc_ctype, icu_locale) == 0))
 		printf(_("The database cluster will be initialized with locale \"%s\".\n"), lc_ctype);
 	else
 	{
@@ -2381,9 +2413,13 @@ setup_locale_encoding(void)
 			   lc_monetary,
 			   lc_numeric,
 			   lc_time);
+		if (icu_locale)
+			printf(_("  ICU:      %s\n"), icu_locale);
 	}
 
-	if (!encoding)
+	if (!encoding && collation_provider[0] == COLLPROVIDER_ICU)
+		encodingid = PG_UTF8;
+	else if (!encoding)
 	{
 		int			ctype_enc;
 
@@ -2887,6 +2923,8 @@ main(int argc, char *argv[])
 		{"data-checksums", no_argument, NULL, 'k'},
 		{"allow-group-access", no_argument, NULL, 'g'},
 		{"discard-caches", no_argument, NULL, 14},
+		{"collation-provider", required_argument, NULL, 15},
+		{"icu-locale", required_argument, NULL, 16},
 		{NULL, 0, NULL, 0}
 	};
 
@@ -3033,6 +3071,20 @@ main(int argc, char *argv[])
 										 extra_options,
 										 "-c debug_discard_caches=1");
 				break;
+			case 15:
+				if (strcmp(optarg, "icu") == 0)
+					collation_provider[0] = COLLPROVIDER_ICU;
+				else if (strcmp(optarg, "libc") == 0)
+					collation_provider[0] = COLLPROVIDER_LIBC;
+				else
+				{
+					pg_log_error("unrecognized collation provider: %s", optarg);
+					exit(1);
+				}
+				break;
+			case 16:
+				icu_locale = pg_strdup(optarg);
+				break;
 			default:
 				/* getopt_long already emitted a complaint */
 				fprintf(stderr, _("Try \"%s --help\" for more information.\n"),
diff --git a/src/bin/initdb/t/001_initdb.pl b/src/bin/initdb/t/001_initdb.pl
index 02bc688a3b..ee6803490c 100644
--- a/src/bin/initdb/t/001_initdb.pl
+++ b/src/bin/initdb/t/001_initdb.pl
@@ -11,7 +11,7 @@
 use File::stat qw{lstat};
 use PostgreSQL::Test::Cluster;
 use PostgreSQL::Test::Utils;
-use Test::More tests => 22;
+use Test::More tests => 24;
 
 my $tempdir = PostgreSQL::Test::Utils::tempdir;
 my $xlogdir = "$tempdir/pgxlog";
@@ -92,3 +92,19 @@
 	ok(check_mode_recursive($datadir_group, 0750, 0640),
 		'check PGDATA permissions');
 }
+
+# Collation provider tests
+
+if ($ENV{with_icu} eq 'yes')
+{
+	command_ok(['initdb', '--no-sync', '--collation-provider=icu', "$tempdir/data2"],
+			   'collation provider ICU');
+}
+else
+{
+	command_fails(['initdb', '--no-sync', '--collation-provider=icu', "$tempdir/data2"],
+				  'collation provider ICU fails since no ICU support');
+}
+
+command_fails(['initdb', '--no-sync', '--collation-provider=xyz', "$tempdir/dataX"],
+			  'fails for invalid collation provider');
diff --git a/src/bin/pg_dump/pg_dump.c b/src/bin/pg_dump/pg_dump.c
index e3ddf19959..0c162f7d42 100644
--- a/src/bin/pg_dump/pg_dump.c
+++ b/src/bin/pg_dump/pg_dump.c
@@ -2753,6 +2753,7 @@ dumpDatabase(Archive *fout)
 				i_datname,
 				i_datdba,
 				i_encoding,
+				i_datcollprovider,
 				i_collate,
 				i_ctype,
 				i_frozenxid,
@@ -2768,6 +2769,7 @@ dumpDatabase(Archive *fout)
 	const char *datname,
 			   *dba,
 			   *encoding,
+			   *datcollprovider,
 			   *collate,
 			   *ctype,
 			   *datistemplate,
@@ -2792,6 +2794,10 @@ dumpDatabase(Archive *fout)
 		appendPQExpBuffer(dbQry, "datminmxid, ");
 	else
 		appendPQExpBuffer(dbQry, "0 AS datminmxid, ");
+	if (fout->remoteVersion >= 150000)
+		appendPQExpBuffer(dbQry, "datcollprovider, ");
+	else
+		appendPQExpBuffer(dbQry, "'c' AS datcollprovider, ");
 	appendPQExpBuffer(dbQry,
 					  "(SELECT spcname FROM pg_tablespace t WHERE t.oid = dattablespace) AS tablespace, "
 					  "shobj_description(oid, 'pg_database') AS description "
@@ -2805,6 +2811,7 @@ dumpDatabase(Archive *fout)
 	i_datname = PQfnumber(res, "datname");
 	i_datdba = PQfnumber(res, "datdba");
 	i_encoding = PQfnumber(res, "encoding");
+	i_datcollprovider = PQfnumber(res, "datcollprovider");
 	i_collate = PQfnumber(res, "datcollate");
 	i_ctype = PQfnumber(res, "datctype");
 	i_frozenxid = PQfnumber(res, "datfrozenxid");
@@ -2820,6 +2827,7 @@ dumpDatabase(Archive *fout)
 	datname = PQgetvalue(res, 0, i_datname);
 	dba = getRoleName(PQgetvalue(res, 0, i_datdba));
 	encoding = PQgetvalue(res, 0, i_encoding);
+	datcollprovider = PQgetvalue(res, 0, i_datcollprovider);
 	collate = PQgetvalue(res, 0, i_collate);
 	ctype = PQgetvalue(res, 0, i_ctype);
 	frozenxid = atooid(PQgetvalue(res, 0, i_frozenxid));
@@ -2853,6 +2861,17 @@ dumpDatabase(Archive *fout)
 		appendPQExpBufferStr(creaQry, " ENCODING = ");
 		appendStringLiteralAH(creaQry, encoding, fout);
 	}
+	if (strlen(datcollprovider) > 0)
+	{
+		appendPQExpBufferStr(creaQry, " COLLATION_PROVIDER = ");
+		if (datcollprovider[0] == 'c')
+			appendPQExpBufferStr(creaQry, "libc");
+		else if (datcollprovider[0] == 'i')
+			appendPQExpBufferStr(creaQry, "icu");
+		else
+			fatal("unrecognized collation provider: %s",
+				  datcollprovider);
+	}
 	if (strlen(collate) > 0 && strcmp(collate, ctype) == 0)
 	{
 		appendPQExpBufferStr(creaQry, " LOCALE = ");
diff --git a/src/bin/pg_upgrade/check.c b/src/bin/pg_upgrade/check.c
index 3d218c2ad2..5c5aa78b2c 100644
--- a/src/bin/pg_upgrade/check.c
+++ b/src/bin/pg_upgrade/check.c
@@ -349,6 +349,16 @@ check_locale_and_encoding(DbInfo *olddb, DbInfo *newdb)
 	if (!equivalent_locale(LC_CTYPE, olddb->db_ctype, newdb->db_ctype))
 		pg_fatal("lc_ctype values for database \"%s\" do not match:  old \"%s\", new \"%s\"\n",
 				 olddb->db_name, olddb->db_ctype, newdb->db_ctype);
+	if (olddb->db_collprovider != newdb->db_collprovider)
+		pg_fatal("collation providers for database \"%s\" do not match:  old \"%c\", new \"%c\"\n",
+				 olddb->db_name, olddb->db_collprovider, newdb->db_collprovider);
+	if ((olddb->db_icucoll == NULL && newdb->db_icucoll != NULL) ||
+		(olddb->db_icucoll != NULL && newdb->db_icucoll == NULL) ||
+		(olddb->db_icucoll != NULL && newdb->db_icucoll != NULL && strcmp(olddb->db_icucoll, newdb->db_icucoll) != 0))
+		pg_fatal("ICU collation values for database \"%s\" do not match:  old \"%s\", new \"%s\"\n",
+				 olddb->db_name,
+				 olddb->db_icucoll ? olddb->db_icucoll : "(null)",
+				 newdb->db_icucoll ? newdb->db_icucoll : "(null)");
 }
 
 /*
diff --git a/src/bin/pg_upgrade/info.c b/src/bin/pg_upgrade/info.c
index 69ef23119f..2a9ca0e389 100644
--- a/src/bin/pg_upgrade/info.c
+++ b/src/bin/pg_upgrade/info.c
@@ -312,11 +312,20 @@ get_db_infos(ClusterInfo *cluster)
 				i_encoding,
 				i_datcollate,
 				i_datctype,
+				i_datcollprovider,
+				i_daticucoll,
 				i_spclocation;
 	char		query[QUERY_ALLOC];
 
 	snprintf(query, sizeof(query),
-			 "SELECT d.oid, d.datname, d.encoding, d.datcollate, d.datctype, "
+			 "SELECT d.oid, d.datname, d.encoding, d.datcollate, d.datctype, ");
+	if (GET_MAJOR_VERSION(old_cluster.major_version) <= 1500)
+		snprintf(query + strlen(query), sizeof(query) - strlen(query),
+				 "'c' AS datcollprovider, NULL AS daticucoll, ");
+	else
+		snprintf(query + strlen(query), sizeof(query) - strlen(query),
+				 "datcollprovider, daticucoll, ");
+	snprintf(query + strlen(query), sizeof(query) - strlen(query),
 			 "pg_catalog.pg_tablespace_location(t.oid) AS spclocation "
 			 "FROM pg_catalog.pg_database d "
 			 " LEFT OUTER JOIN pg_catalog.pg_tablespace t "
@@ -331,6 +340,8 @@ get_db_infos(ClusterInfo *cluster)
 	i_encoding = PQfnumber(res, "encoding");
 	i_datcollate = PQfnumber(res, "datcollate");
 	i_datctype = PQfnumber(res, "datctype");
+	i_datcollprovider = PQfnumber(res, "datcollprovider");
+	i_daticucoll = PQfnumber(res, "daticucoll");
 	i_spclocation = PQfnumber(res, "spclocation");
 
 	ntups = PQntuples(res);
@@ -343,6 +354,11 @@ get_db_infos(ClusterInfo *cluster)
 		dbinfos[tupnum].db_encoding = atoi(PQgetvalue(res, tupnum, i_encoding));
 		dbinfos[tupnum].db_collate = pg_strdup(PQgetvalue(res, tupnum, i_datcollate));
 		dbinfos[tupnum].db_ctype = pg_strdup(PQgetvalue(res, tupnum, i_datctype));
+		dbinfos[tupnum].db_collprovider = PQgetvalue(res, tupnum, i_datcollprovider)[0];
+		if (PQgetisnull(res, tupnum, i_daticucoll))
+			dbinfos[tupnum].db_icucoll = NULL;
+		else
+			dbinfos[tupnum].db_icucoll = pg_strdup(PQgetvalue(res, tupnum, i_daticucoll));
 		snprintf(dbinfos[tupnum].db_tablespace, sizeof(dbinfos[tupnum].db_tablespace), "%s",
 				 PQgetvalue(res, tupnum, i_spclocation));
 	}
diff --git a/src/bin/pg_upgrade/pg_upgrade.h b/src/bin/pg_upgrade/pg_upgrade.h
index 1db8e3f0fb..5c0f256598 100644
--- a/src/bin/pg_upgrade/pg_upgrade.h
+++ b/src/bin/pg_upgrade/pg_upgrade.h
@@ -163,6 +163,8 @@ typedef struct
 											 * path */
 	char	   *db_collate;
 	char	   *db_ctype;
+	char		db_collprovider;
+	char	   *db_icucoll;
 	int			db_encoding;
 	RelInfoArr	rel_arr;		/* array of all user relinfos */
 } DbInfo;
diff --git a/src/bin/psql/describe.c b/src/bin/psql/describe.c
index 346cd92793..b85a7b1794 100644
--- a/src/bin/psql/describe.c
+++ b/src/bin/psql/describe.c
@@ -896,6 +896,18 @@ listAllDbs(const char *pattern, bool verbose)
 					  gettext_noop("Encoding"),
 					  gettext_noop("Collate"),
 					  gettext_noop("Ctype"));
+	if (pset.sversion >= 150000)
+		appendPQExpBuffer(&buf,
+						  "       d.daticucoll as \"%s\",\n"
+						  "       CASE d.datcollprovider WHEN 'c' THEN 'libc' WHEN 'i' THEN 'icu' END AS \"%s\",\n",
+						  gettext_noop("ICU Collation"),
+						  gettext_noop("Coll. Provider"));
+	else
+		appendPQExpBuffer(&buf,
+						  "       d.datcollate as \"%s\",\n"
+						  "       'libc' AS \"%s\",\n",
+						  gettext_noop("ICU Collation"),
+						  gettext_noop("Coll. Provider"));
 	appendPQExpBufferStr(&buf, "       ");
 	printACLColumn(&buf, "d.datacl");
 	if (verbose)
@@ -4603,7 +4615,7 @@ listCollations(const char *pattern, bool verbose, bool showSystem)
 	PQExpBufferData buf;
 	PGresult   *res;
 	printQueryOpt myopt = pset.popt;
-	static const bool translate_columns[] = {false, false, false, false, false, true, false};
+	static const bool translate_columns[] = {false, false, false, false, false, false, true, false};
 
 	initPQExpBuffer(&buf);
 
@@ -4617,6 +4629,15 @@ listCollations(const char *pattern, bool verbose, bool showSystem)
 					  gettext_noop("Collate"),
 					  gettext_noop("Ctype"));
 
+	if (pset.sversion >= 150000)
+		appendPQExpBuffer(&buf,
+						  ",\n       c.collicucoll AS \"%s\"",
+						  gettext_noop("ICU Collation"));
+	else
+		appendPQExpBuffer(&buf,
+						  ",\n       c.collcollate AS \"%s\"",
+						  gettext_noop("ICU Collation"));
+
 	if (pset.sversion >= 100000)
 		appendPQExpBuffer(&buf,
 						  ",\n       CASE c.collprovider WHEN 'd' THEN 'default' WHEN 'c' THEN 'libc' WHEN 'i' THEN 'icu' END AS \"%s\"",
diff --git a/src/bin/psql/tab-complete.c b/src/bin/psql/tab-complete.c
index 0ee94d7362..ff05d395e0 100644
--- a/src/bin/psql/tab-complete.c
+++ b/src/bin/psql/tab-complete.c
@@ -2716,7 +2716,7 @@ psql_completion(const char *text, int start, int end)
 		COMPLETE_WITH("OWNER", "TEMPLATE", "ENCODING", "TABLESPACE",
 					  "IS_TEMPLATE",
 					  "ALLOW_CONNECTIONS", "CONNECTION LIMIT",
-					  "LC_COLLATE", "LC_CTYPE", "LOCALE", "OID");
+					  "LC_COLLATE", "LC_CTYPE", "LOCALE", "OID", "COLLATION_PROVIDER");
 
 	else if (Matches("CREATE", "DATABASE", MatchAny, "TEMPLATE"))
 		COMPLETE_WITH_QUERY(Query_for_list_of_template_databases);
diff --git a/src/bin/scripts/Makefile b/src/bin/scripts/Makefile
index b833109da6..25e7da3d3f 100644
--- a/src/bin/scripts/Makefile
+++ b/src/bin/scripts/Makefile
@@ -53,6 +53,8 @@ clean distclean maintainer-clean:
 	rm -f common.o $(WIN32RES)
 	rm -rf tmp_check
 
+export with_icu
+
 check:
 	$(prove_check)
 
diff --git a/src/bin/scripts/createdb.c b/src/bin/scripts/createdb.c
index b0c6805bc9..471cae7cca 100644
--- a/src/bin/scripts/createdb.c
+++ b/src/bin/scripts/createdb.c
@@ -38,6 +38,7 @@ main(int argc, char *argv[])
 		{"lc-ctype", required_argument, NULL, 2},
 		{"locale", required_argument, NULL, 'l'},
 		{"maintenance-db", required_argument, NULL, 3},
+		{"collation-provider", required_argument, NULL, 4},
 		{NULL, 0, NULL, 0}
 	};
 
@@ -61,6 +62,7 @@ main(int argc, char *argv[])
 	char	   *lc_collate = NULL;
 	char	   *lc_ctype = NULL;
 	char	   *locale = NULL;
+	char	   *collation_provider = NULL;
 
 	PQExpBufferData sql;
 
@@ -119,6 +121,9 @@ main(int argc, char *argv[])
 			case 3:
 				maintenance_db = pg_strdup(optarg);
 				break;
+			case 4:
+				collation_provider = pg_strdup(optarg);
+				break;
 			default:
 				fprintf(stderr, _("Try \"%s --help\" for more information.\n"), progname);
 				exit(1);
@@ -217,6 +222,8 @@ main(int argc, char *argv[])
 		appendPQExpBufferStr(&sql, " LC_CTYPE ");
 		appendStringLiteralConn(&sql, lc_ctype, conn);
 	}
+	if (collation_provider)
+		appendPQExpBuffer(&sql, " COLLATION_PROVIDER %s", collation_provider);
 
 	appendPQExpBufferChar(&sql, ';');
 
@@ -267,6 +274,8 @@ help(const char *progname)
 	printf(_("Usage:\n"));
 	printf(_("  %s [OPTION]... [DBNAME] [DESCRIPTION]\n"), progname);
 	printf(_("\nOptions:\n"));
+	printf(_("      --collation-provider={libc|icu}\n"
+			 "                               collation provider for the database's default collation\n"));
 	printf(_("  -D, --tablespace=TABLESPACE  default tablespace for the database\n"));
 	printf(_("  -e, --echo                   show the commands being sent to the server\n"));
 	printf(_("  -E, --encoding=ENCODING      encoding for the database\n"));
diff --git a/src/bin/scripts/t/020_createdb.pl b/src/bin/scripts/t/020_createdb.pl
index c54c291b7a..9712714a46 100644
--- a/src/bin/scripts/t/020_createdb.pl
+++ b/src/bin/scripts/t/020_createdb.pl
@@ -6,7 +6,7 @@
 
 use PostgreSQL::Test::Cluster;
 use PostgreSQL::Test::Utils;
-use Test::More tests => 25;
+use Test::More tests => 28;
 
 program_help_ok('createdb');
 program_version_ok('createdb');
@@ -25,9 +25,27 @@
 	qr/statement: CREATE DATABASE foobar2 ENCODING 'LATIN1'/,
 	'create database with encoding');
 
+if ($ENV{with_icu} eq 'yes')
+{
+	$node->issues_sql_like(
+		[ 'createdb', '-T', 'template0', '--collation-provider=icu', 'foobar4' ],
+		qr/statement: CREATE DATABASE foobar4 .* COLLATION_PROVIDER icu/,
+		'create database with ICU');
+}
+else
+{
+	$node->command_fails(
+		[ 'createdb', '-T', 'template0', '--collation-provider=icu', 'foobar4' ],
+		'create database with ICU fails since no ICU support');
+	pass;
+}
+
 $node->command_fails([ 'createdb', 'foobar1' ],
 	'fails if database already exists');
 
+$node->command_fails([ 'createdb', '-T', 'template0', '--collation-provider=xyz', 'foobarX' ],
+	'fails for invalid collation provider');
+
 # Check use of templates with shared dependencies copied from the template.
 my ($ret, $stdout, $stderr) = $node->psql(
 	'foobar2',
diff --git a/src/include/catalog/pg_collation.dat b/src/include/catalog/pg_collation.dat
index 4b56825d82..f7470ead49 100644
--- a/src/include/catalog/pg_collation.dat
+++ b/src/include/catalog/pg_collation.dat
@@ -14,8 +14,7 @@
 
 { oid => '100', oid_symbol => 'DEFAULT_COLLATION_OID',
   descr => 'database\'s default collation',
-  collname => 'default', collprovider => 'd', collencoding => '-1',
-  collcollate => '', collctype => '' },
+  collname => 'default', collprovider => 'd', collencoding => '-1' },
 { oid => '950', oid_symbol => 'C_COLLATION_OID',
   descr => 'standard C collation',
   collname => 'C', collprovider => 'c', collencoding => '-1',
diff --git a/src/include/catalog/pg_collation.h b/src/include/catalog/pg_collation.h
index 8763dd4080..590e06d1a8 100644
--- a/src/include/catalog/pg_collation.h
+++ b/src/include/catalog/pg_collation.h
@@ -40,8 +40,9 @@ CATALOG(pg_collation,3456,CollationRelationId)
 	bool		collisdeterministic BKI_DEFAULT(t);
 	int32		collencoding;	/* encoding for this collation; -1 = "all" */
 #ifdef CATALOG_VARLEN			/* variable-length fields start here */
-	text		collcollate BKI_FORCE_NOT_NULL;		/* LC_COLLATE setting */
-	text		collctype BKI_FORCE_NOT_NULL;		/* LC_CTYPE setting */
+	text		collcollate BKI_DEFAULT(_null_);	/* LC_COLLATE setting */
+	text		collctype BKI_DEFAULT(_null_);		/* LC_CTYPE setting */
+	text		collicucoll BKI_DEFAULT(_null_);	/* ICU collation string */
 	text		collversion BKI_DEFAULT(_null_);	/* provider-dependent
 													 * version of collation
 													 * data */
@@ -75,6 +76,7 @@ extern Oid	CollationCreate(const char *collname, Oid collnamespace,
 							bool collisdeterministic,
 							int32 collencoding,
 							const char *collcollate, const char *collctype,
+							const char *collicucoll,
 							const char *collversion,
 							bool if_not_exists,
 							bool quiet);
diff --git a/src/include/catalog/pg_database.dat b/src/include/catalog/pg_database.dat
index e7e42d6023..cce12e27bd 100644
--- a/src/include/catalog/pg_database.dat
+++ b/src/include/catalog/pg_database.dat
@@ -14,9 +14,9 @@
 
 { oid => '1', oid_symbol => 'TemplateDbOid',
   descr => 'default template for new databases',
-  datname => 'template1', encoding => 'ENCODING', datistemplate => 't',
+  datname => 'template1', encoding => 'ENCODING', datcollprovider => 'COLLPROVIDER', datistemplate => 't',
   datallowconn => 't', datconnlimit => '-1', datfrozenxid => '0',
   datminmxid => '1', dattablespace => 'pg_default', datcollate => 'LC_COLLATE',
-  datctype => 'LC_CTYPE', datacl => '_null_' },
+  datctype => 'LC_CTYPE', daticucoll => 'ICUCOLL', datacl => '_null_' },
 
 ]
diff --git a/src/include/catalog/pg_database.h b/src/include/catalog/pg_database.h
index 90b43a4ecc..13dc5e1ba9 100644
--- a/src/include/catalog/pg_database.h
+++ b/src/include/catalog/pg_database.h
@@ -40,6 +40,9 @@ CATALOG(pg_database,1262,DatabaseRelationId) BKI_SHARED_RELATION BKI_ROWTYPE_OID
 	/* character encoding */
 	int32		encoding;
 
+	/* see pg_collation.collprovider */
+	char		datcollprovider;
+
 	/* allowed as CREATE DATABASE template? */
 	bool		datistemplate;
 
@@ -65,6 +68,9 @@ CATALOG(pg_database,1262,DatabaseRelationId) BKI_SHARED_RELATION BKI_ROWTYPE_OID
 	/* LC_CTYPE setting */
 	text		datctype BKI_FORCE_NOT_NULL;
 
+	/* ICU collation */
+	text		daticucoll;
+
 	/* access permissions */
 	aclitem		datacl[1];
 #endif
diff --git a/src/include/utils/pg_locale.h b/src/include/utils/pg_locale.h
index 30e423af0e..11138e02f3 100644
--- a/src/include/utils/pg_locale.h
+++ b/src/include/utils/pg_locale.h
@@ -103,6 +103,12 @@ struct pg_locale_struct
 
 typedef struct pg_locale_struct *pg_locale_t;
 
+extern struct pg_locale_struct default_locale;
+
+extern void make_icu_collator(const char *icucollstr,
+							  struct pg_locale_struct *resultp);
+extern void check_collation_version(HeapTuple colltuple);
+
 extern pg_locale_t pg_newlocale_from_collation(Oid collid);
 
 extern char *get_collation_actual_version(char collprovider, const char *collcollate);
diff --git a/src/test/regress/expected/collate.icu.utf8.out b/src/test/regress/expected/collate.icu.utf8.out
index 70133df804..3d9647b597 100644
--- a/src/test/regress/expected/collate.icu.utf8.out
+++ b/src/test/regress/expected/collate.icu.utf8.out
@@ -1029,14 +1029,12 @@ CREATE COLLATION test0 FROM "C"; -- fail, duplicate name
 ERROR:  collation "test0" already exists
 do $$
 BEGIN
-  EXECUTE 'CREATE COLLATION test1 (provider = icu, lc_collate = ' ||
-          quote_literal(current_setting('lc_collate')) ||
-          ', lc_ctype = ' ||
-          quote_literal(current_setting('lc_ctype')) || ');';
+  EXECUTE 'CREATE COLLATION test1 (provider = icu, locale = ' ||
+          quote_literal(current_setting('lc_collate')) || ');';
 END
 $$;
-CREATE COLLATION test3 (provider = icu, lc_collate = 'en_US.utf8'); -- fail, need lc_ctype
-ERROR:  parameter "lc_ctype" must be specified
+CREATE COLLATION test3 (provider = icu, lc_collate = 'en_US.utf8'); -- fail, needs "locale"
+ERROR:  parameter "locale" must be specified
 CREATE COLLATION testx (provider = icu, locale = 'nonsense'); /* never fails with ICU */  DROP COLLATION testx;
 CREATE COLLATION test4 FROM nonsense;
 ERROR:  collation "nonsense" for encoding "UTF8" does not exist
diff --git a/src/test/regress/sql/collate.icu.utf8.sql b/src/test/regress/sql/collate.icu.utf8.sql
index 9cee3d0042..0677ba56e4 100644
--- a/src/test/regress/sql/collate.icu.utf8.sql
+++ b/src/test/regress/sql/collate.icu.utf8.sql
@@ -366,13 +366,11 @@ CREATE SCHEMA test_schema;
 CREATE COLLATION test0 FROM "C"; -- fail, duplicate name
 do $$
 BEGIN
-  EXECUTE 'CREATE COLLATION test1 (provider = icu, lc_collate = ' ||
-          quote_literal(current_setting('lc_collate')) ||
-          ', lc_ctype = ' ||
-          quote_literal(current_setting('lc_ctype')) || ');';
+  EXECUTE 'CREATE COLLATION test1 (provider = icu, locale = ' ||
+          quote_literal(current_setting('lc_collate')) || ');';
 END
 $$;
-CREATE COLLATION test3 (provider = icu, lc_collate = 'en_US.utf8'); -- fail, need lc_ctype
+CREATE COLLATION test3 (provider = icu, lc_collate = 'en_US.utf8'); -- fail, needs "locale"
 CREATE COLLATION testx (provider = icu, locale = 'nonsense'); /* never fails with ICU */  DROP COLLATION testx;
 
 CREATE COLLATION test4 FROM nonsense;

base-commit: 87669de72c2249e6aec84b8c27fdc3ffb7284e13
-- 
2.35.1

From 6d265e2cf78546bcc25d03031ea03f397f1c1c1b Mon Sep 17 00:00:00 2001
From: Peter Eisentraut <peter@eisentraut.org>
Date: Wed, 16 Feb 2022 15:11:04 +0100
Subject: [PATCH v5] Add option to use ICU as global locale provider

This adds the option to use ICU as the default locale provider for
either the whole cluster or a database.  New options for initdb,
createdb, and CREATE DATABASE are used to select this.

Discussion: https://www.postgresql.org/message-id/flat/5e756dd6-0e91-d778-96fd-b1bcb06c161a%402ndquadrant.com

XXX catversion bump
---
 doc/src/sgml/catalogs.sgml                    |   9 +
 doc/src/sgml/ref/create_database.sgml         |  27 +++
 doc/src/sgml/ref/createdb.sgml                |  19 ++
 doc/src/sgml/ref/initdb.sgml                  |  76 ++++++--
 src/backend/catalog/pg_collation.c            |  18 +-
 src/backend/commands/collationcmds.c          |  96 +++++++----
 src/backend/commands/dbcommands.c             | 162 +++++++++++++++---
 src/backend/utils/adt/pg_locale.c             | 144 ++++++++++------
 src/backend/utils/init/postinit.c             |  21 ++-
 src/bin/initdb/Makefile                       |   4 +-
 src/bin/initdb/initdb.c                       | 110 ++++++++++--
 src/bin/initdb/t/001_initdb.pl                |  25 +++
 src/bin/pg_dump/pg_dump.c                     |  31 +++-
 src/bin/pg_upgrade/check.c                    |  13 ++
 src/bin/pg_upgrade/info.c                     |  18 +-
 src/bin/pg_upgrade/pg_upgrade.h               |   2 +
 src/bin/psql/describe.c                       |  23 ++-
 src/bin/psql/tab-complete.c                   |   3 +-
 src/bin/scripts/Makefile                      |   2 +
 src/bin/scripts/createdb.c                    |  20 +++
 src/bin/scripts/t/020_createdb.pl             |  28 +++
 src/include/catalog/pg_collation.dat          |   3 +-
 src/include/catalog/pg_collation.h            |  20 ++-
 src/include/catalog/pg_database.dat           |   4 +-
 src/include/catalog/pg_database.h             |   6 +
 src/include/utils/pg_locale.h                 |   5 +
 .../regress/expected/collate.icu.utf8.out     |  10 +-
 src/test/regress/sql/collate.icu.utf8.sql     |   8 +-
 28 files changed, 741 insertions(+), 166 deletions(-)

diff --git a/doc/src/sgml/catalogs.sgml b/doc/src/sgml/catalogs.sgml
index 5a1627a394..8fde32dfac 100644
--- a/doc/src/sgml/catalogs.sgml
+++ b/doc/src/sgml/catalogs.sgml
@@ -2384,6 +2384,15 @@ <title><structname>pg_collation</structname> Columns</title>
       </para></entry>
      </row>
 
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
+       <structfield>colliculocale</structfield> <type>text</type>
+      </para>
+      <para>
+       ICU locale ID for this collation object
+      </para></entry>
+     </row>
+
      <row>
       <entry role="catalog_table_entry"><para role="column_definition">
        <structfield>collversion</structfield> <type>text</type>
diff --git a/doc/src/sgml/ref/create_database.sgml b/doc/src/sgml/ref/create_database.sgml
index f70d0c75b4..544c1cb443 100644
--- a/doc/src/sgml/ref/create_database.sgml
+++ b/doc/src/sgml/ref/create_database.sgml
@@ -28,6 +28,8 @@
            [ LOCALE [=] <replaceable class="parameter">locale</replaceable> ]
            [ LC_COLLATE [=] <replaceable class="parameter">lc_collate</replaceable> ]
            [ LC_CTYPE [=] <replaceable class="parameter">lc_ctype</replaceable> ]
+           [ ICU_LOCALE [=] <replaceable class="parameter">icu_locale</replaceable> ]
+           [ LOCALE_PROVIDER [=] <replaceable class="parameter">locale_provider</replaceable> ]
            [ COLLATION_VERSION = <replaceable>collation_version</replaceable> ]
            [ TABLESPACE [=] <replaceable class="parameter">tablespace_name</replaceable> ]
            [ ALLOW_CONNECTIONS [=] <replaceable class="parameter">allowconn</replaceable> ]
@@ -160,6 +162,31 @@ <title>Parameters</title>
       </listitem>
      </varlistentry>
 
+     <varlistentry>
+      <term><replaceable class="parameter">icu_locale</replaceable></term>
+      <listitem>
+       <para>
+        Specifies the ICU locale if the ICU locale provider is used.  If
+        this is not specified, the value from the <literal>LOCALE</literal>
+        option is used.
+       </para>
+      </listitem>
+     </varlistentry>
+
+     <varlistentry>
+      <term><replaceable>locale_provider</replaceable></term>
+
+      <listitem>
+       <para>
+        Specifies the provider to use for the default collation in this
+        database.  Possible values are:
+        <literal>icu</literal>,<indexterm><primary>ICU</primary></indexterm>
+        <literal>libc</literal>.  <literal>libc</literal> is the default.  The
+        available choices depend on the operating system and build options.
+       </para>
+      </listitem>
+     </varlistentry>
+
      <varlistentry>
       <term><replaceable>collation_version</replaceable></term>
 
diff --git a/doc/src/sgml/ref/createdb.sgml b/doc/src/sgml/ref/createdb.sgml
index 86473455c9..ebed1df30b 100644
--- a/doc/src/sgml/ref/createdb.sgml
+++ b/doc/src/sgml/ref/createdb.sgml
@@ -147,6 +147,25 @@ <title>Options</title>
       </listitem>
      </varlistentry>
 
+     <varlistentry>
+      <term><option>--icu-locale=<replaceable class="parameter">locale</replaceable></option></term>
+      <listitem>
+       <para>
+        Specifies the ICU locale setting to be used in this database, if the
+        ICU locale provider is selected.
+       </para>
+      </listitem>
+     </varlistentry>
+
+     <varlistentry>
+      <term><option>--locale-provider={<literal>libc</literal>|<literal>icu</literal>}</option></term>
+      <listitem>
+       <para>
+        Specifies the locale provider for the database's default collation.
+       </para>
+      </listitem>
+     </varlistentry>
+
      <varlistentry>
       <term><option>-O <replaceable class="parameter">owner</replaceable></option></term>
       <term><option>--owner=<replaceable class="parameter">owner</replaceable></option></term>
diff --git a/doc/src/sgml/ref/initdb.sgml b/doc/src/sgml/ref/initdb.sgml
index 8f71c7c962..31f4450755 100644
--- a/doc/src/sgml/ref/initdb.sgml
+++ b/doc/src/sgml/ref/initdb.sgml
@@ -86,30 +86,47 @@ <title>Description</title>
   </para>
 
   <para>
-   <command>initdb</command> initializes the database cluster's default
-   locale and character set encoding. The character set encoding,
-   collation order (<literal>LC_COLLATE</literal>) and character set classes
-   (<literal>LC_CTYPE</literal>, e.g., upper, lower, digit) can be set separately
-   for a database when it is created. <command>initdb</command> determines
-   those settings for the template databases, which will
-   serve as the default for all other databases.
+   <command>initdb</command> initializes the database cluster's default locale
+   and character set encoding. These can also be set separately for each
+   database when it is created. <command>initdb</command> determines those
+   settings for the template databases, which will serve as the default for
+   all other databases.  By default, <command>initdb</command> uses the
+   locale provider <literal>libc</literal>, takes the locale settings from
+   the environment, and determines the encoding from the locale settings.
+   This is almost always sufficient, unless there are special requirements.
   </para>
 
   <para>
-   To alter the default collation order or character set classes, use the
-   <option>--lc-collate</option> and <option>--lc-ctype</option> options.
-   Collation orders other than <literal>C</literal> or <literal>POSIX</literal> also have
-   a performance penalty.  For these reasons it is important to choose the
-   right locale when running <command>initdb</command>.
+   To choose a different locale for the cluster, use the option
+   <option>--locale</option>.  There are also individual options
+   <option>--lc-*</option> (see below) to set values for the individual locale
+   categories.  Note that inconsistent settings for different locale
+   categories can give nonsensical results, so this should be used with care.
   </para>
 
   <para>
-   The remaining locale categories can be changed later when the server
-   is started.  You can also use <option>--locale</option> to set the
-   default for all locale categories, including collation order and
-   character set classes. All server locale values (<literal>lc_*</literal>) can
-   be displayed via <command>SHOW ALL</command>.
-   More details can be found in <xref linkend="locale"/>.
+   Alternatively, the ICU library can be used to provide locale services.
+   (Again, this only sets the default for subsequently created databases.)  To
+   select this option, specify <literal>--locale-provider=icu</literal>.
+   To chose the specific ICU locale ID to apply, use the option
+   <option>--icu-locale</option>.  The ICU locale ID defaults to
+   <option>--locale</option> or the environment, as above (with some name
+   mangling applied to make the locale naming appropriate for ICU).  Note that
+   for implementation reasons and to support legacy code,
+   <command>initdb</command> will still select and initialize libc locale
+   settings when the ICU locale provider is used.
+  </para>
+
+  <para>
+   When <command>initdb</command> runs, it will print out the locale settings
+   it has chosen.  If you have complex requirements or specified multiple
+   options, it is advisable to check that the result matches what was
+   intended.
+  </para>
+
+  <para>
+   More details about locale settings can be found in <xref
+   linkend="locale"/>.
   </para>
 
   <para>
@@ -210,6 +227,17 @@ <title>Options</title>
       </listitem>
      </varlistentry>
 
+     <varlistentry>
+      <term><option>--icu-locale=<replaceable>locale</replaceable></option></term>
+      <listitem>
+       <para>
+        Specifies the ICU locale if the ICU locale provider is used.  If
+        this is not specified, the value from the <option>--locale</option>
+        option is used.
+       </para>
+      </listitem>
+     </varlistentry>
+
      <varlistentry id="app-initdb-data-checksums" xreflabel="data checksums">
       <term><option>-k</option></term>
       <term><option>--data-checksums</option></term>
@@ -264,6 +292,18 @@ <title>Options</title>
       </listitem>
      </varlistentry>
 
+     <varlistentry>
+      <term><option>--locale-provider={<literal>libc</literal>|<literal>icu</literal>}</option></term>
+      <listitem>
+       <para>
+        This option sets the locale provider for databases created in the
+        new cluster.  It can be overridden in the <command>CREATE
+        DATABASE</command> command when new databases are subsequently
+        created.  The default is <literal>libc</literal>.
+       </para>
+      </listitem>
+     </varlistentry>
+
      <varlistentry>
       <term><option>-N</option></term>
       <term><option>--no-sync</option></term>
diff --git a/src/backend/catalog/pg_collation.c b/src/backend/catalog/pg_collation.c
index bfc02d3038..93545786df 100644
--- a/src/backend/catalog/pg_collation.c
+++ b/src/backend/catalog/pg_collation.c
@@ -49,6 +49,7 @@ CollationCreate(const char *collname, Oid collnamespace,
 				bool collisdeterministic,
 				int32 collencoding,
 				const char *collcollate, const char *collctype,
+				const char *colliculocale,
 				const char *collversion,
 				bool if_not_exists,
 				bool quiet)
@@ -66,8 +67,7 @@ CollationCreate(const char *collname, Oid collnamespace,
 	AssertArg(collname);
 	AssertArg(collnamespace);
 	AssertArg(collowner);
-	AssertArg(collcollate);
-	AssertArg(collctype);
+	AssertArg((collcollate && collctype) || colliculocale);
 
 	/*
 	 * Make sure there is no existing collation of same name & encoding.
@@ -161,8 +161,18 @@ CollationCreate(const char *collname, Oid collnamespace,
 	values[Anum_pg_collation_collprovider - 1] = CharGetDatum(collprovider);
 	values[Anum_pg_collation_collisdeterministic - 1] = BoolGetDatum(collisdeterministic);
 	values[Anum_pg_collation_collencoding - 1] = Int32GetDatum(collencoding);
-	values[Anum_pg_collation_collcollate - 1] = CStringGetTextDatum(collcollate);
-	values[Anum_pg_collation_collctype - 1] = CStringGetTextDatum(collctype);
+	if (collcollate)
+		values[Anum_pg_collation_collcollate - 1] = CStringGetTextDatum(collcollate);
+	else
+		nulls[Anum_pg_collation_collcollate - 1] = true;
+	if (collctype)
+		values[Anum_pg_collation_collctype - 1] = CStringGetTextDatum(collctype);
+	else
+		nulls[Anum_pg_collation_collctype - 1] = true;
+	if (colliculocale)
+		values[Anum_pg_collation_colliculocale - 1] = CStringGetTextDatum(colliculocale);
+	else
+		nulls[Anum_pg_collation_colliculocale - 1] = true;
 	if (collversion)
 		values[Anum_pg_collation_collversion - 1] = CStringGetTextDatum(collversion);
 	else
diff --git a/src/backend/commands/collationcmds.c b/src/backend/commands/collationcmds.c
index 12fc2316f9..9777b63f16 100644
--- a/src/backend/commands/collationcmds.c
+++ b/src/backend/commands/collationcmds.c
@@ -65,6 +65,7 @@ DefineCollation(ParseState *pstate, List *names, List *parameters, bool if_not_e
 	DefElem    *versionEl = NULL;
 	char	   *collcollate = NULL;
 	char	   *collctype = NULL;
+	char	   *colliculocale = NULL;
 	char	   *collproviderstr = NULL;
 	bool		collisdeterministic = true;
 	int			collencoding = 0;
@@ -153,6 +154,12 @@ DefineCollation(ParseState *pstate, List *names, List *parameters, bool if_not_e
 		else
 			collctype = NULL;
 
+		datum = SysCacheGetAttr(COLLOID, tp, Anum_pg_collation_colliculocale, &isnull);
+		if (!isnull)
+			colliculocale = TextDatumGetCString(datum);
+		else
+			colliculocale = NULL;
+
 		ReleaseSysCache(tp);
 
 		/*
@@ -168,18 +175,6 @@ DefineCollation(ParseState *pstate, List *names, List *parameters, bool if_not_e
 					 errmsg("collation \"default\" cannot be copied")));
 	}
 
-	if (localeEl)
-	{
-		collcollate = defGetString(localeEl);
-		collctype = defGetString(localeEl);
-	}
-
-	if (lccollateEl)
-		collcollate = defGetString(lccollateEl);
-
-	if (lcctypeEl)
-		collctype = defGetString(lcctypeEl);
-
 	if (providerEl)
 		collproviderstr = defGetString(providerEl);
 
@@ -204,15 +199,43 @@ DefineCollation(ParseState *pstate, List *names, List *parameters, bool if_not_e
 	else if (!fromEl)
 		collprovider = COLLPROVIDER_LIBC;
 
-	if (!collcollate)
-		ereport(ERROR,
-				(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
-				 errmsg("parameter \"lc_collate\" must be specified")));
+	if (localeEl)
+	{
+		if (collprovider == COLLPROVIDER_LIBC)
+		{
+			collcollate = defGetString(localeEl);
+			collctype = defGetString(localeEl);
+		}
+		else
+			colliculocale = defGetString(localeEl);
+	}
 
-	if (!collctype)
-		ereport(ERROR,
-				(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
-				 errmsg("parameter \"lc_ctype\" must be specified")));
+	if (lccollateEl)
+		collcollate = defGetString(lccollateEl);
+
+	if (lcctypeEl)
+		collctype = defGetString(lcctypeEl);
+
+	if (collprovider == COLLPROVIDER_LIBC)
+	{
+		if (!collcollate)
+			ereport(ERROR,
+					(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
+					 errmsg("parameter \"lc_collate\" must be specified")));
+
+		if (!collctype)
+			ereport(ERROR,
+					(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
+					 errmsg("parameter \"lc_ctype\" must be specified")));
+	}
+
+	if (collprovider == COLLPROVIDER_ICU)
+	{
+		if (!colliculocale)
+			ereport(ERROR,
+					(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
+					 errmsg("parameter \"locale\" must be specified")));
+	}
 
 	/*
 	 * Nondeterministic collations are currently only supported with ICU
@@ -255,7 +278,7 @@ DefineCollation(ParseState *pstate, List *names, List *parameters, bool if_not_e
 	}
 
 	if (!collversion)
-		collversion = get_collation_actual_version(collprovider, collcollate);
+		collversion = get_collation_actual_version(collprovider, collprovider == COLLPROVIDER_ICU ? colliculocale : collcollate);
 
 	newoid = CollationCreate(collName,
 							 collNamespace,
@@ -265,6 +288,7 @@ DefineCollation(ParseState *pstate, List *names, List *parameters, bool if_not_e
 							 collencoding,
 							 collcollate,
 							 collctype,
+							 colliculocale,
 							 collversion,
 							 if_not_exists,
 							 false);	/* not quiet */
@@ -347,9 +371,11 @@ AlterCollation(AlterCollationStmt *stmt)
 	datum = SysCacheGetAttr(COLLOID, tup, Anum_pg_collation_collversion, &isnull);
 	oldversion = isnull ? NULL : TextDatumGetCString(datum);
 
-	datum = SysCacheGetAttr(COLLOID, tup, Anum_pg_collation_collcollate, &isnull);
-	Assert(!isnull);
-	newversion = get_collation_actual_version(collForm->collprovider, TextDatumGetCString(datum));
+	datum = SysCacheGetAttr(COLLOID, tup, collForm->collprovider == COLLPROVIDER_ICU ? Anum_pg_collation_colliculocale : Anum_pg_collation_collcollate, &isnull);
+	if (!isnull)
+		newversion = get_collation_actual_version(collForm->collprovider, TextDatumGetCString(datum));
+	else
+		newversion = NULL;
 
 	/* cannot change from NULL to non-NULL or vice versa */
 	if ((!oldversion && newversion) || (oldversion && !newversion))
@@ -409,9 +435,11 @@ pg_collation_actual_version(PG_FUNCTION_ARGS)
 
 	collprovider = ((Form_pg_collation) GETSTRUCT(tp))->collprovider;
 
-	datum = SysCacheGetAttr(COLLOID, tp, Anum_pg_collation_collcollate, &isnull);
-	Assert(!isnull);
-	version = get_collation_actual_version(collprovider, TextDatumGetCString(datum));
+	datum = SysCacheGetAttr(COLLOID, tp, collprovider == COLLPROVIDER_ICU ? Anum_pg_collation_colliculocale : Anum_pg_collation_collcollate, &isnull);
+	if (!isnull)
+		version = get_collation_actual_version(collprovider, TextDatumGetCString(datum));
+	else
+		version = NULL;
 
 	ReleaseSysCache(tp);
 
@@ -638,7 +666,7 @@ pg_import_system_collations(PG_FUNCTION_ARGS)
 			 */
 			collid = CollationCreate(localebuf, nspid, GetUserId(),
 									 COLLPROVIDER_LIBC, true, enc,
-									 localebuf, localebuf,
+									 localebuf, localebuf, NULL,
 									 get_collation_actual_version(COLLPROVIDER_LIBC, localebuf),
 									 true, true);
 			if (OidIsValid(collid))
@@ -699,7 +727,7 @@ pg_import_system_collations(PG_FUNCTION_ARGS)
 
 			collid = CollationCreate(alias, nspid, GetUserId(),
 									 COLLPROVIDER_LIBC, true, enc,
-									 locale, locale,
+									 locale, locale, NULL,
 									 get_collation_actual_version(COLLPROVIDER_LIBC, locale),
 									 true, true);
 			if (OidIsValid(collid))
@@ -740,7 +768,7 @@ pg_import_system_collations(PG_FUNCTION_ARGS)
 			const char *name;
 			char	   *langtag;
 			char	   *icucomment;
-			const char *collcollate;
+			const char *iculocstr;
 			Oid			collid;
 
 			if (i == -1)
@@ -749,20 +777,20 @@ pg_import_system_collations(PG_FUNCTION_ARGS)
 				name = uloc_getAvailable(i);
 
 			langtag = get_icu_language_tag(name);
-			collcollate = U_ICU_VERSION_MAJOR_NUM >= 54 ? langtag : name;
+			iculocstr = U_ICU_VERSION_MAJOR_NUM >= 54 ? langtag : name;
 
 			/*
 			 * Be paranoid about not allowing any non-ASCII strings into
 			 * pg_collation
 			 */
-			if (!pg_is_ascii(langtag) || !pg_is_ascii(collcollate))
+			if (!pg_is_ascii(langtag) || !pg_is_ascii(iculocstr))
 				continue;
 
 			collid = CollationCreate(psprintf("%s-x-icu", langtag),
 									 nspid, GetUserId(),
 									 COLLPROVIDER_ICU, true, -1,
-									 collcollate, collcollate,
-									 get_collation_actual_version(COLLPROVIDER_ICU, collcollate),
+									 NULL, NULL, iculocstr,
+									 get_collation_actual_version(COLLPROVIDER_ICU, iculocstr),
 									 true, true);
 			if (OidIsValid(collid))
 			{
diff --git a/src/backend/commands/dbcommands.c b/src/backend/commands/dbcommands.c
index c37e3c9a9a..6598a91ed0 100644
--- a/src/backend/commands/dbcommands.c
+++ b/src/backend/commands/dbcommands.c
@@ -86,7 +86,8 @@ static bool get_db_info(const char *name, LOCKMODE lockmode,
 						Oid *dbIdP, Oid *ownerIdP,
 						int *encodingP, bool *dbIsTemplateP, bool *dbAllowConnP,
 						TransactionId *dbFrozenXidP, MultiXactId *dbMinMultiP,
-						Oid *dbTablespace, char **dbCollate, char **dbCtype,
+						Oid *dbTablespace, char **dbCollate, char **dbCtype, char **dbIculocale,
+						char *dbLocProvider,
 						char **dbCollversion);
 static bool have_createdb_privilege(void);
 static void remove_dbtablespaces(Oid db_id);
@@ -107,6 +108,8 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 	int			src_encoding = -1;
 	char	   *src_collate = NULL;
 	char	   *src_ctype = NULL;
+	char	   *src_iculocale = NULL;
+	char		src_locprovider;
 	char	   *src_collversion = NULL;
 	bool		src_istemplate;
 	bool		src_allowconn;
@@ -128,6 +131,8 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 	DefElem    *dlocale = NULL;
 	DefElem    *dcollate = NULL;
 	DefElem    *dctype = NULL;
+	DefElem    *diculocale = NULL;
+	DefElem	   *dlocprovider = NULL;
 	DefElem    *distemplate = NULL;
 	DefElem    *dallowconnections = NULL;
 	DefElem    *dconnlimit = NULL;
@@ -137,6 +142,8 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 	const char *dbtemplate = NULL;
 	char	   *dbcollate = NULL;
 	char	   *dbctype = NULL;
+	char	   *dbiculocale = NULL;
+	char		dblocprovider = '\0';
 	char	   *canonname;
 	int			encoding = -1;
 	bool		dbistemplate = false;
@@ -194,6 +201,21 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 				errorConflictingDefElem(defel, pstate);
 			dctype = defel;
 		}
+		else if (strcmp(defel->defname, "icu_locale") == 0)
+		{
+			if (diculocale)
+				errorConflictingDefElem(defel, pstate);
+			diculocale = defel;
+		}
+		else if (strcmp(defel->defname, "locale_provider") == 0)
+		{
+			if (dlocprovider)
+				ereport(ERROR,
+						(errcode(ERRCODE_SYNTAX_ERROR),
+						 errmsg("conflicting or redundant options"),
+						 parser_errposition(pstate, defel->location)));
+			dlocprovider = defel;
+		}
 		else if (strcmp(defel->defname, "is_template") == 0)
 		{
 			if (distemplate)
@@ -257,12 +279,6 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 					 parser_errposition(pstate, defel->location)));
 	}
 
-	if (dlocale && (dcollate || dctype))
-		ereport(ERROR,
-				(errcode(ERRCODE_SYNTAX_ERROR),
-				 errmsg("conflicting or redundant options"),
-				 errdetail("LOCALE cannot be specified together with LC_COLLATE or LC_CTYPE.")));
-
 	if (downer && downer->arg)
 		dbowner = defGetString(downer);
 	if (dtemplate && dtemplate->arg)
@@ -304,6 +320,31 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 		dbcollate = defGetString(dcollate);
 	if (dctype && dctype->arg)
 		dbctype = defGetString(dctype);
+	if (diculocale && diculocale->arg)
+		dbiculocale = defGetString(diculocale);
+	if (dlocprovider && dlocprovider->arg)
+	{
+		char	   *locproviderstr = defGetString(dlocprovider);
+
+		if (pg_strcasecmp(locproviderstr, "icu") == 0)
+			dblocprovider = COLLPROVIDER_ICU;
+		else if (pg_strcasecmp(locproviderstr, "libc") == 0)
+			dblocprovider = COLLPROVIDER_LIBC;
+		else
+			ereport(ERROR,
+					(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
+					 errmsg("unrecognized locale provider: %s",
+							locproviderstr)));
+	}
+	if (diculocale && dblocprovider != COLLPROVIDER_ICU)
+		ereport(ERROR,
+				(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
+				 errmsg("ICU locale cannot be specified unless locale provider is ICU")));
+	if (dblocprovider == COLLPROVIDER_ICU && !dbiculocale)
+	{
+		if (dlocale && dlocale->arg)
+			dbiculocale = defGetString(dlocale);
+	}
 	if (distemplate && distemplate->arg)
 		dbistemplate = defGetBoolean(distemplate);
 	if (dallowconnections && dallowconnections->arg)
@@ -355,7 +396,8 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 					 &src_dboid, &src_owner, &src_encoding,
 					 &src_istemplate, &src_allowconn,
 					 &src_frozenxid, &src_minmxid, &src_deftablespace,
-					 &src_collate, &src_ctype, &src_collversion))
+					 &src_collate, &src_ctype, &src_iculocale, &src_locprovider,
+					 &src_collversion))
 		ereport(ERROR,
 				(errcode(ERRCODE_UNDEFINED_DATABASE),
 				 errmsg("template database \"%s\" does not exist",
@@ -381,6 +423,10 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 		dbcollate = src_collate;
 	if (dbctype == NULL)
 		dbctype = src_ctype;
+	if (dbiculocale == NULL)
+		dbiculocale = src_iculocale;
+	if (dblocprovider == '\0')
+		dblocprovider = src_locprovider;
 
 	/* Some encodings are client only */
 	if (!PG_VALID_BE_ENCODING(encoding))
@@ -402,6 +448,37 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 
 	check_encoding_locale_matches(encoding, dbcollate, dbctype);
 
+	if (dblocprovider == COLLPROVIDER_ICU)
+	{
+		/*
+		 * This would happen if template0 uses the libc provider but the new
+		 * database uses icu.
+		 */
+		if (!dbiculocale)
+			ereport(ERROR,
+					(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+					 errmsg("ICU locale must be specified")));
+	}
+
+	if (dblocprovider == COLLPROVIDER_ICU)
+	{
+#ifdef USE_ICU
+		UErrorCode  status;
+
+		status = U_ZERO_ERROR;
+		ucol_open(dbiculocale, &status);
+		if (U_FAILURE(status))
+			ereport(ERROR,
+					(errmsg("could not open collator for locale \"%s\": %s",
+							dbiculocale, u_errorName(status))));
+#else
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				 errmsg("ICU is not supported in this build"), \
+				 errhint("You need to rebuild PostgreSQL using %s.", "--with-icu")));
+#endif
+	}
+
 	/*
 	 * Check that the new encoding and locale settings match the source
 	 * database.  We insist on this because we simply copy the source data ---
@@ -435,6 +512,25 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 					 errmsg("new LC_CTYPE (%s) is incompatible with the LC_CTYPE of the template database (%s)",
 							dbctype, src_ctype),
 					 errhint("Use the same LC_CTYPE as in the template database, or use template0 as template.")));
+
+		if (dblocprovider != src_locprovider)
+			ereport(ERROR,
+					(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+					 errmsg("new locale provider (%c) does not match locale provider of the template database (%c)",
+							dblocprovider, src_locprovider),
+					 errhint("Use the same locale provider as in the template database, or use template0 as template.")));
+
+		if (dblocprovider == COLLPROVIDER_ICU)
+		{
+			Assert(dbiculocale);
+			Assert(src_iculocale);
+			if (strcmp(dbiculocale, src_iculocale) != 0)
+				ereport(ERROR,
+						(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+						 errmsg("new ICU locale (%s) is incompatible with the ICU locale of the template database (%s)",
+								dbiculocale, src_iculocale),
+						 errhint("Use the same ICU locale as in the template database, or use template0 as template.")));
+		}
 	}
 
 	/*
@@ -453,7 +549,7 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 	{
 		char	   *actual_versionstr;
 
-		actual_versionstr = get_collation_actual_version(COLLPROVIDER_LIBC, dbcollate);
+		actual_versionstr = get_collation_actual_version(dblocprovider, dblocprovider == COLLPROVIDER_ICU ? dbiculocale : dbcollate);
 		if (!actual_versionstr)
 			ereport(ERROR,
 					(errmsg("template database \"%s\" has a collation version, but no actual collation version could be determined",
@@ -481,7 +577,7 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 	 * collation version, which is normally only the case for template0.
 	 */
 	if (dbcollversion == NULL)
-		dbcollversion = get_collation_actual_version(COLLPROVIDER_LIBC, dbcollate);
+		dbcollversion = get_collation_actual_version(dblocprovider, dblocprovider == COLLPROVIDER_ICU ? dbiculocale : dbcollate);
 
 	/* Resolve default tablespace for new database */
 	if (dtablespacename && dtablespacename->arg)
@@ -620,6 +716,9 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 	 * block on the unique index, and fail after we commit).
 	 */
 
+	Assert((dblocprovider == COLLPROVIDER_ICU && dbiculocale) ||
+		   (dblocprovider != COLLPROVIDER_ICU && !dbiculocale));
+
 	/* Form tuple */
 	MemSet(new_record, 0, sizeof(new_record));
 	MemSet(new_record_nulls, false, sizeof(new_record_nulls));
@@ -629,6 +728,7 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 		DirectFunctionCall1(namein, CStringGetDatum(dbname));
 	new_record[Anum_pg_database_datdba - 1] = ObjectIdGetDatum(datdba);
 	new_record[Anum_pg_database_encoding - 1] = Int32GetDatum(encoding);
+	new_record[Anum_pg_database_datlocprovider - 1] = CharGetDatum(dblocprovider);
 	new_record[Anum_pg_database_datistemplate - 1] = BoolGetDatum(dbistemplate);
 	new_record[Anum_pg_database_datallowconn - 1] = BoolGetDatum(dballowconnections);
 	new_record[Anum_pg_database_datconnlimit - 1] = Int32GetDatum(dbconnlimit);
@@ -637,6 +737,10 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 	new_record[Anum_pg_database_dattablespace - 1] = ObjectIdGetDatum(dst_deftablespace);
 	new_record[Anum_pg_database_datcollate - 1] = CStringGetTextDatum(dbcollate);
 	new_record[Anum_pg_database_datctype - 1] = CStringGetTextDatum(dbctype);
+	if (dbiculocale)
+		new_record[Anum_pg_database_daticulocale - 1] = CStringGetTextDatum(dbiculocale);
+	else
+		new_record_nulls[Anum_pg_database_daticulocale - 1] = true;
 	if (dbcollversion)
 		new_record[Anum_pg_database_datcollversion - 1] = CStringGetTextDatum(dbcollversion);
 	else
@@ -907,7 +1011,7 @@ dropdb(const char *dbname, bool missing_ok, bool force)
 	pgdbrel = table_open(DatabaseRelationId, RowExclusiveLock);
 
 	if (!get_db_info(dbname, AccessExclusiveLock, &db_id, NULL, NULL,
-					 &db_istemplate, NULL, NULL, NULL, NULL, NULL, NULL, NULL))
+					 &db_istemplate, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL))
 	{
 		if (!missing_ok)
 		{
@@ -1109,7 +1213,7 @@ RenameDatabase(const char *oldname, const char *newname)
 	rel = table_open(DatabaseRelationId, RowExclusiveLock);
 
 	if (!get_db_info(oldname, AccessExclusiveLock, &db_id, NULL, NULL,
-					 NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL))
+					 NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL))
 		ereport(ERROR,
 				(errcode(ERRCODE_UNDEFINED_DATABASE),
 				 errmsg("database \"%s\" does not exist", oldname)));
@@ -1222,7 +1326,7 @@ movedb(const char *dbname, const char *tblspcname)
 	pgdbrel = table_open(DatabaseRelationId, RowExclusiveLock);
 
 	if (!get_db_info(dbname, AccessExclusiveLock, &db_id, NULL, NULL,
-					 NULL, NULL, NULL, NULL, &src_tblspcoid, NULL, NULL, NULL))
+					 NULL, NULL, NULL, NULL, &src_tblspcoid, NULL, NULL, NULL, NULL, NULL))
 		ereport(ERROR,
 				(errcode(ERRCODE_UNDEFINED_DATABASE),
 				 errmsg("database \"%s\" does not exist", dbname)));
@@ -1755,9 +1859,11 @@ AlterDatabaseRefreshColl(AlterDatabaseRefreshCollStmt *stmt)
 	datum = heap_getattr(tuple, Anum_pg_database_datcollversion, RelationGetDescr(rel), &isnull);
 	oldversion = isnull ? NULL : TextDatumGetCString(datum);
 
-	datum = heap_getattr(tuple, Anum_pg_database_datcollate, RelationGetDescr(rel), &isnull);
-	Assert(!isnull);
-	newversion = get_collation_actual_version(COLLPROVIDER_LIBC, TextDatumGetCString(datum));
+	datum = heap_getattr(tuple, datForm->datlocprovider == COLLPROVIDER_ICU ? Anum_pg_database_daticulocale : Anum_pg_database_datcollate, RelationGetDescr(rel), &isnull);
+	if (!isnull)
+		newversion = get_collation_actual_version(datForm->datlocprovider, TextDatumGetCString(datum));
+	else
+		newversion = NULL;
 
 	/* cannot change from NULL to non-NULL or vice versa */
 	if ((!oldversion && newversion) || (oldversion && !newversion))
@@ -1943,6 +2049,7 @@ pg_database_collation_actual_version(PG_FUNCTION_ARGS)
 {
 	Oid			dbid = PG_GETARG_OID(0);
 	HeapTuple	tp;
+	char		datlocprovider;
 	Datum		datum;
 	bool		isnull;
 	char	   *version;
@@ -1953,9 +2060,13 @@ pg_database_collation_actual_version(PG_FUNCTION_ARGS)
 				(errcode(ERRCODE_UNDEFINED_OBJECT),
 				 errmsg("database with OID %u does not exist", dbid)));
 
-	datum = SysCacheGetAttr(DATABASEOID, tp, Anum_pg_database_datcollate, &isnull);
-	Assert(!isnull);
-	version = get_collation_actual_version(COLLPROVIDER_LIBC, TextDatumGetCString(datum));
+	datlocprovider = ((Form_pg_database) GETSTRUCT(tp))->datlocprovider;
+
+	datum = SysCacheGetAttr(DATABASEOID, tp, datlocprovider == COLLPROVIDER_ICU ? Anum_pg_database_daticulocale : Anum_pg_database_datcollate, &isnull);
+	if (!isnull)
+		version = get_collation_actual_version(datlocprovider, TextDatumGetCString(datum));
+	else
+		version = NULL;
 
 	ReleaseSysCache(tp);
 
@@ -1981,7 +2092,8 @@ get_db_info(const char *name, LOCKMODE lockmode,
 			Oid *dbIdP, Oid *ownerIdP,
 			int *encodingP, bool *dbIsTemplateP, bool *dbAllowConnP,
 			TransactionId *dbFrozenXidP, MultiXactId *dbMinMultiP,
-			Oid *dbTablespace, char **dbCollate, char **dbCtype,
+			Oid *dbTablespace, char **dbCollate, char **dbCtype, char **dbIculocale,
+			char *dbLocProvider,
 			char **dbCollversion)
 {
 	bool		result = false;
@@ -2075,6 +2187,8 @@ get_db_info(const char *name, LOCKMODE lockmode,
 				if (dbTablespace)
 					*dbTablespace = dbform->dattablespace;
 				/* default locale settings for this database */
+				if (dbLocProvider)
+					*dbLocProvider = dbform->datlocprovider;
 				if (dbCollate)
 				{
 					datum = SysCacheGetAttr(DATABASEOID, tuple, Anum_pg_database_datcollate, &isnull);
@@ -2087,6 +2201,14 @@ get_db_info(const char *name, LOCKMODE lockmode,
 					Assert(!isnull);
 					*dbCtype = TextDatumGetCString(datum);
 				}
+				if (dbIculocale)
+				{
+					datum = SysCacheGetAttr(DATABASEOID, tuple, Anum_pg_database_daticulocale, &isnull);
+					if (isnull)
+						*dbIculocale = NULL;
+					else
+						*dbIculocale = TextDatumGetCString(datum);
+				}
 				if (dbCollversion)
 				{
 					datum = SysCacheGetAttr(DATABASEOID, tuple, Anum_pg_database_datcollversion, &isnull);
diff --git a/src/backend/utils/adt/pg_locale.c b/src/backend/utils/adt/pg_locale.c
index 871a710967..2ca75330ee 100644
--- a/src/backend/utils/adt/pg_locale.c
+++ b/src/backend/utils/adt/pg_locale.c
@@ -1288,26 +1288,37 @@ lookup_collation_cache(Oid collation, bool set_flags)
 	{
 		/* Attempt to set the flags */
 		HeapTuple	tp;
-		Datum		datum;
-		bool		isnull;
-		const char *collcollate;
-		const char *collctype;
+		Form_pg_collation collform;
 
 		tp = SearchSysCache1(COLLOID, ObjectIdGetDatum(collation));
 		if (!HeapTupleIsValid(tp))
 			elog(ERROR, "cache lookup failed for collation %u", collation);
+		collform = (Form_pg_collation) GETSTRUCT(tp);
 
-		datum = SysCacheGetAttr(COLLOID, tp, Anum_pg_collation_collcollate, &isnull);
-		Assert(!isnull);
-		collcollate = TextDatumGetCString(datum);
-		datum = SysCacheGetAttr(COLLOID, tp, Anum_pg_collation_collctype, &isnull);
-		Assert(!isnull);
-		collctype = TextDatumGetCString(datum);
-
-		cache_entry->collate_is_c = ((strcmp(collcollate, "C") == 0) ||
-									 (strcmp(collcollate, "POSIX") == 0));
-		cache_entry->ctype_is_c = ((strcmp(collctype, "C") == 0) ||
-								   (strcmp(collctype, "POSIX") == 0));
+		if (collform->collprovider == COLLPROVIDER_LIBC)
+		{
+			Datum		datum;
+			bool		isnull;
+			const char *collcollate;
+			const char *collctype;
+
+			datum = SysCacheGetAttr(COLLOID, tp, Anum_pg_collation_collcollate, &isnull);
+			Assert(!isnull);
+			collcollate = TextDatumGetCString(datum);
+			datum = SysCacheGetAttr(COLLOID, tp, Anum_pg_collation_collctype, &isnull);
+			Assert(!isnull);
+			collctype = TextDatumGetCString(datum);
+
+			cache_entry->collate_is_c = ((strcmp(collcollate, "C") == 0) ||
+										 (strcmp(collcollate, "POSIX") == 0));
+			cache_entry->ctype_is_c = ((strcmp(collctype, "C") == 0) ||
+									   (strcmp(collctype, "POSIX") == 0));
+		}
+		else
+		{
+			cache_entry->collate_is_c = false;
+			cache_entry->ctype_is_c = false;
+		}
 
 		cache_entry->flags_valid = true;
 
@@ -1340,6 +1351,9 @@ lc_collate_is_c(Oid collation)
 		static int	result = -1;
 		char	   *localeptr;
 
+		if (default_locale.provider == COLLPROVIDER_ICU)
+			return false;
+
 		if (result >= 0)
 			return (bool) result;
 		localeptr = setlocale(LC_COLLATE, NULL);
@@ -1390,6 +1404,9 @@ lc_ctype_is_c(Oid collation)
 		static int	result = -1;
 		char	   *localeptr;
 
+		if (default_locale.provider == COLLPROVIDER_ICU)
+			return false;
+
 		if (result >= 0)
 			return (bool) result;
 		localeptr = setlocale(LC_CTYPE, NULL);
@@ -1418,6 +1435,38 @@ lc_ctype_is_c(Oid collation)
 	return (lookup_collation_cache(collation, true))->ctype_is_c;
 }
 
+struct pg_locale_struct default_locale;
+
+void
+make_icu_collator(const char *iculocstr,
+				  struct pg_locale_struct *resultp)
+{
+#ifdef USE_ICU
+	UCollator  *collator;
+	UErrorCode	status;
+
+	status = U_ZERO_ERROR;
+	collator = ucol_open(iculocstr, &status);
+	if (U_FAILURE(status))
+		ereport(ERROR,
+				(errmsg("could not open collator for locale \"%s\": %s",
+						iculocstr, u_errorName(status))));
+
+	if (U_ICU_VERSION_MAJOR_NUM < 54)
+		icu_set_collation_attributes(collator, iculocstr);
+
+	/* We will leak this string if we get an error below :-( */
+	resultp->info.icu.locale = MemoryContextStrdup(TopMemoryContext, iculocstr);
+	resultp->info.icu.ucol = collator;
+#else							/* not USE_ICU */
+	/* could get here if a collation was created by a build with ICU */
+	ereport(ERROR,
+			(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+			 errmsg("ICU is not supported in this build"), \
+			 errhint("You need to rebuild PostgreSQL using %s.", "--with-icu")));
+#endif							/* not USE_ICU */
+}
+
 
 /* simple subroutine for reporting errors from newlocale() */
 #ifdef HAVE_LOCALE_T
@@ -1475,7 +1524,12 @@ pg_newlocale_from_collation(Oid collid)
 	Assert(OidIsValid(collid));
 
 	if (collid == DEFAULT_COLLATION_OID)
-		return (pg_locale_t) 0;
+	{
+		if (default_locale.provider == COLLPROVIDER_ICU)
+			return &default_locale;
+		else
+			return (pg_locale_t) 0;
+	}
 
 	cache_entry = lookup_collation_cache(collid, false);
 
@@ -1484,8 +1538,6 @@ pg_newlocale_from_collation(Oid collid)
 		/* We haven't computed this yet in this session, so do it */
 		HeapTuple	tp;
 		Form_pg_collation collform;
-		const char *collcollate;
-		const char *collctype pg_attribute_unused();
 		struct pg_locale_struct result;
 		pg_locale_t resultp;
 		Datum		datum;
@@ -1496,13 +1548,6 @@ pg_newlocale_from_collation(Oid collid)
 			elog(ERROR, "cache lookup failed for collation %u", collid);
 		collform = (Form_pg_collation) GETSTRUCT(tp);
 
-		datum = SysCacheGetAttr(COLLOID, tp, Anum_pg_collation_collcollate, &isnull);
-		Assert(!isnull);
-		collcollate = TextDatumGetCString(datum);
-		datum = SysCacheGetAttr(COLLOID, tp, Anum_pg_collation_collctype, &isnull);
-		Assert(!isnull);
-		collctype = TextDatumGetCString(datum);
-
 		/* We'll fill in the result struct locally before allocating memory */
 		memset(&result, 0, sizeof(result));
 		result.provider = collform->collprovider;
@@ -1511,8 +1556,17 @@ pg_newlocale_from_collation(Oid collid)
 		if (collform->collprovider == COLLPROVIDER_LIBC)
 		{
 #ifdef HAVE_LOCALE_T
+			const char *collcollate;
+			const char *collctype pg_attribute_unused();
 			locale_t	loc;
 
+			datum = SysCacheGetAttr(COLLOID, tp, Anum_pg_collation_collcollate, &isnull);
+			Assert(!isnull);
+			collcollate = TextDatumGetCString(datum);
+			datum = SysCacheGetAttr(COLLOID, tp, Anum_pg_collation_collctype, &isnull);
+			Assert(!isnull);
+			collctype = TextDatumGetCString(datum);
+
 			if (strcmp(collcollate, collctype) == 0)
 			{
 				/* Normal case where they're the same */
@@ -1563,36 +1617,12 @@ pg_newlocale_from_collation(Oid collid)
 		}
 		else if (collform->collprovider == COLLPROVIDER_ICU)
 		{
-#ifdef USE_ICU
-			UCollator  *collator;
-			UErrorCode	status;
-
-			if (strcmp(collcollate, collctype) != 0)
-				ereport(ERROR,
-						(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-						 errmsg("collations with different collate and ctype values are not supported by ICU")));
-
-			status = U_ZERO_ERROR;
-			collator = ucol_open(collcollate, &status);
-			if (U_FAILURE(status))
-				ereport(ERROR,
-						(errmsg("could not open collator for locale \"%s\": %s",
-								collcollate, u_errorName(status))));
+			const char *iculocstr;
 
-			if (U_ICU_VERSION_MAJOR_NUM < 54)
-				icu_set_collation_attributes(collator, collcollate);
-
-			/* We will leak this string if we get an error below :-( */
-			result.info.icu.locale = MemoryContextStrdup(TopMemoryContext,
-														 collcollate);
-			result.info.icu.ucol = collator;
-#else							/* not USE_ICU */
-			/* could get here if a collation was created by a build with ICU */
-			ereport(ERROR,
-					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-					 errmsg("ICU is not supported in this build"), \
-					 errhint("You need to rebuild PostgreSQL using %s.", "--with-icu")));
-#endif							/* not USE_ICU */
+			datum = SysCacheGetAttr(COLLOID, tp, Anum_pg_collation_colliculocale, &isnull);
+			Assert(!isnull);
+			iculocstr = TextDatumGetCString(datum);
+			make_icu_collator(iculocstr, &result);
 		}
 
 		datum = SysCacheGetAttr(COLLOID, tp, Anum_pg_collation_collversion,
@@ -1604,7 +1634,11 @@ pg_newlocale_from_collation(Oid collid)
 
 			collversionstr = TextDatumGetCString(datum);
 
-			actual_versionstr = get_collation_actual_version(collform->collprovider, collcollate);
+			datum = SysCacheGetAttr(COLLOID, tp, collform->collprovider == COLLPROVIDER_ICU ? Anum_pg_collation_colliculocale : Anum_pg_collation_collcollate, &isnull);
+			Assert(!isnull);
+
+			actual_versionstr = get_collation_actual_version(collform->collprovider,
+															 TextDatumGetCString(datum));
 			if (!actual_versionstr)
 			{
 				/*
diff --git a/src/backend/utils/init/postinit.c b/src/backend/utils/init/postinit.c
index e2208151e4..37b02106eb 100644
--- a/src/backend/utils/init/postinit.c
+++ b/src/backend/utils/init/postinit.c
@@ -318,6 +318,7 @@ CheckMyDatabase(const char *name, bool am_superuser, bool override_allow_connect
 	bool		isnull;
 	char	   *collate;
 	char	   *ctype;
+	char	   *iculocale;
 
 	/* Fetch our pg_database row normally, via syscache */
 	tup = SearchSysCache1(DATABASEOID, ObjectIdGetDatum(MyDatabaseId));
@@ -420,6 +421,24 @@ CheckMyDatabase(const char *name, bool am_superuser, bool override_allow_connect
 						   " which is not recognized by setlocale().", ctype),
 				 errhint("Recreate the database with another locale or install the missing locale.")));
 
+	if (dbform->datlocprovider == COLLPROVIDER_ICU)
+	{
+		datum = SysCacheGetAttr(DATABASEOID, tup, Anum_pg_database_daticulocale, &isnull);
+		Assert(!isnull);
+		iculocale = TextDatumGetCString(datum);
+		make_icu_collator(iculocale, &default_locale);
+	}
+	else
+		iculocale = NULL;
+
+	default_locale.provider = dbform->datlocprovider;
+	/*
+	 * Default locale is currently always deterministic.  Nondeterministic
+	 * locales currently don't support pattern matching, which would break a
+	 * lot of things if applied globally.
+	 */
+	default_locale.deterministic = true;
+
 	/*
 	 * Check collation version.  See similar code in
 	 * pg_newlocale_from_collation().  Note that here we warn instead of error
@@ -434,7 +453,7 @@ CheckMyDatabase(const char *name, bool am_superuser, bool override_allow_connect
 
 		collversionstr = TextDatumGetCString(datum);
 
-		actual_versionstr = get_collation_actual_version(COLLPROVIDER_LIBC, collate);
+		actual_versionstr = get_collation_actual_version(dbform->datlocprovider, dbform->datlocprovider == COLLPROVIDER_ICU ? iculocale : collate);
 		if (!actual_versionstr)
 			ereport(WARNING,
 					(errmsg("database \"%s\" has no actual collation version, but a version was recorded",
diff --git a/src/bin/initdb/Makefile b/src/bin/initdb/Makefile
index eba282267a..8dd25e7afc 100644
--- a/src/bin/initdb/Makefile
+++ b/src/bin/initdb/Makefile
@@ -40,7 +40,7 @@ OBJS = \
 all: initdb
 
 initdb: $(OBJS) | submake-libpq submake-libpgport submake-libpgfeutils
-	$(CC) $(CFLAGS) $(OBJS) $(LDFLAGS) $(LDFLAGS_EX) $(LIBS) -o $@$(X)
+	$(CC) $(CFLAGS) $(OBJS) $(LDFLAGS) $(LDFLAGS_EX) $(LIBS) $(ICU_LIBS) -o $@$(X)
 
 # We must pull in localtime.c from src/timezones
 localtime.c: % : $(top_srcdir)/src/timezone/%
@@ -62,6 +62,8 @@ clean distclean maintainer-clean:
 # ensure that changes in datadir propagate into object file
 initdb.o: initdb.c $(top_builddir)/src/Makefile.global
 
+export with_icu
+
 check:
 	$(prove_check)
 
diff --git a/src/bin/initdb/initdb.c b/src/bin/initdb/initdb.c
index 97f15971e2..a0fd68e739 100644
--- a/src/bin/initdb/initdb.c
+++ b/src/bin/initdb/initdb.c
@@ -55,6 +55,10 @@
 #include <signal.h>
 #include <time.h>
 
+#ifdef USE_ICU
+#include <unicode/ucol.h>
+#endif
+
 #ifdef HAVE_SHM_OPEN
 #include "sys/mman.h"
 #endif
@@ -132,6 +136,8 @@ static char *lc_monetary = NULL;
 static char *lc_numeric = NULL;
 static char *lc_time = NULL;
 static char *lc_messages = NULL;
+static char locale_provider = COLLPROVIDER_LIBC;
+static char *icu_locale = NULL;
 static const char *default_text_search_config = NULL;
 static char *username = NULL;
 static bool pwprompt = false;
@@ -1405,6 +1411,12 @@ bootstrap_template1(void)
 	bki_lines = replace_token(bki_lines, "LC_CTYPE",
 							  escape_quotes_bki(lc_ctype));
 
+	bki_lines = replace_token(bki_lines, "ICU_LOCALE",
+							  locale_provider == COLLPROVIDER_ICU ? escape_quotes_bki(icu_locale) : "_null_");
+
+	sprintf(buf, "%c", locale_provider);
+	bki_lines = replace_token(bki_lines, "LOCALE_PROVIDER", buf);
+
 	/* Also ensure backend isn't confused by this environment var: */
 	unsetenv("PGCLIENTENCODING");
 
@@ -2165,7 +2177,6 @@ setlocales(void)
 	 * canonicalize locale names, and obtain any missing values from our
 	 * current environment
 	 */
-
 	check_locale_name(LC_CTYPE, lc_ctype, &canonname);
 	lc_ctype = canonname;
 	check_locale_name(LC_COLLATE, lc_collate, &canonname);
@@ -2184,6 +2195,50 @@ setlocales(void)
 	check_locale_name(LC_CTYPE, lc_messages, &canonname);
 	lc_messages = canonname;
 #endif
+
+	if (locale_provider == COLLPROVIDER_ICU)
+	{
+		if (!icu_locale && locale)
+			icu_locale = locale;
+
+		/*
+		 * If ICU is selected but no ICU locale has been given, take the
+		 * lc_collate locale and chop off any encoding suffix.  This should
+		 * give the user a configuration that resembles their operating
+		 * system's locale setup.
+		 *
+		 * See
+		 * <https://unicode-org.github.io/icu/userguide/locale/#the-locale-concept>
+		 * for the ICU locale ID format.
+		 */
+		if (!icu_locale)
+		{
+			icu_locale = pg_strdup(lc_collate);
+			icu_locale[strcspn(icu_locale, ".")] = '\0';
+		}
+
+		/*
+		 * Check ICU locale name
+		 */
+#ifdef USE_ICU
+		{
+			UErrorCode	status;
+
+			status = U_ZERO_ERROR;
+			ucol_open(icu_locale, &status);
+			if (U_FAILURE(status))
+			{
+				pg_log_error("could not open collator for locale \"%s\": %s",
+							 icu_locale, u_errorName(status));
+				exit(1);
+			}
+		}
+#else
+		pg_log_error("ICU is not supported in this build");
+		fprintf(stderr, _("You need to rebuild PostgreSQL using %s.\n"), "--with-icu");
+		exit(1);
+#endif
+	}
 }
 
 /*
@@ -2202,6 +2257,7 @@ usage(const char *progname)
 	printf(_(" [-D, --pgdata=]DATADIR     location for this database cluster\n"));
 	printf(_("  -E, --encoding=ENCODING   set default encoding for new databases\n"));
 	printf(_("  -g, --allow-group-access  allow group read/execute on data directory\n"));
+	printf(_("      --icu-locale          set ICU locale for new databases\n"));
 	printf(_("  -k, --data-checksums      use data page checksums\n"));
 	printf(_("      --locale=LOCALE       set default locale for new databases\n"));
 	printf(_("      --lc-collate=, --lc-ctype=, --lc-messages=LOCALE\n"
@@ -2209,6 +2265,8 @@ usage(const char *progname)
 			 "                            set default locale in the respective category for\n"
 			 "                            new databases (default taken from environment)\n"));
 	printf(_("      --no-locale           equivalent to --locale=C\n"));
+	printf(_("      --locale-provider={libc|icu}\n"
+			 "                            set default locale provider for new databases\n"));
 	printf(_("      --pwfile=FILE         read password for the new superuser from file\n"));
 	printf(_("  -T, --text-search-config=CFG\n"
 			 "                            default text search configuration\n"));
@@ -2372,21 +2430,26 @@ setup_locale_encoding(void)
 {
 	setlocales();
 
-	if (strcmp(lc_ctype, lc_collate) == 0 &&
+	if (locale_provider == COLLPROVIDER_LIBC &&
+		strcmp(lc_ctype, lc_collate) == 0 &&
 		strcmp(lc_ctype, lc_time) == 0 &&
 		strcmp(lc_ctype, lc_numeric) == 0 &&
 		strcmp(lc_ctype, lc_monetary) == 0 &&
-		strcmp(lc_ctype, lc_messages) == 0)
+		strcmp(lc_ctype, lc_messages) == 0 &&
+		(!icu_locale || strcmp(lc_ctype, icu_locale) == 0))
 		printf(_("The database cluster will be initialized with locale \"%s\".\n"), lc_ctype);
 	else
 	{
-		printf(_("The database cluster will be initialized with locales\n"
-				 "  COLLATE:  %s\n"
-				 "  CTYPE:    %s\n"
-				 "  MESSAGES: %s\n"
-				 "  MONETARY: %s\n"
-				 "  NUMERIC:  %s\n"
-				 "  TIME:     %s\n"),
+		printf(_("The database cluster will be initialized with this locale configuration:\n"));
+		printf(_("  provider:    %s\n"), collprovider_name(locale_provider));
+		if (icu_locale)
+			printf(_("  ICU locale:  %s\n"), icu_locale);
+		printf(_("  LC_COLLATE:  %s\n"
+				 "  LC_CTYPE:    %s\n"
+				 "  LC_MESSAGES: %s\n"
+				 "  LC_MONETARY: %s\n"
+				 "  LC_NUMERIC:  %s\n"
+				 "  LC_TIME:     %s\n"),
 			   lc_collate,
 			   lc_ctype,
 			   lc_messages,
@@ -2395,7 +2458,9 @@ setup_locale_encoding(void)
 			   lc_time);
 	}
 
-	if (!encoding)
+	if (!encoding && locale_provider == COLLPROVIDER_ICU)
+		encodingid = PG_UTF8;
+	else if (!encoding)
 	{
 		int			ctype_enc;
 
@@ -2899,6 +2964,8 @@ main(int argc, char *argv[])
 		{"data-checksums", no_argument, NULL, 'k'},
 		{"allow-group-access", no_argument, NULL, 'g'},
 		{"discard-caches", no_argument, NULL, 14},
+		{"locale-provider", required_argument, NULL, 15},
+		{"icu-locale", required_argument, NULL, 16},
 		{NULL, 0, NULL, 0}
 	};
 
@@ -3045,6 +3112,20 @@ main(int argc, char *argv[])
 										 extra_options,
 										 "-c debug_discard_caches=1");
 				break;
+			case 15:
+				if (strcmp(optarg, "icu") == 0)
+					locale_provider = COLLPROVIDER_ICU;
+				else if (strcmp(optarg, "libc") == 0)
+					locale_provider = COLLPROVIDER_LIBC;
+				else
+				{
+					pg_log_error("unrecognized locale provider: %s", optarg);
+					exit(1);
+				}
+				break;
+			case 16:
+				icu_locale = pg_strdup(optarg);
+				break;
 			default:
 				/* getopt_long already emitted a complaint */
 				fprintf(stderr, _("Try \"%s --help\" for more information.\n"),
@@ -3073,6 +3154,13 @@ main(int argc, char *argv[])
 		exit(1);
 	}
 
+	if (icu_locale && locale_provider != COLLPROVIDER_ICU)
+	{
+		pg_log_error("%s cannot be specified unless locale provider \"%s\" is chosen",
+					 "--icu-locale", "icu");
+		exit(1);
+	}
+
 	atexit(cleanup_directories_atexit);
 
 	/* If we only need to fsync, just do it and exit */
diff --git a/src/bin/initdb/t/001_initdb.pl b/src/bin/initdb/t/001_initdb.pl
index 7dc8cdd855..b7ecff17d8 100644
--- a/src/bin/initdb/t/001_initdb.pl
+++ b/src/bin/initdb/t/001_initdb.pl
@@ -93,4 +93,29 @@
 		'check PGDATA permissions');
 }
 
+# Locale provider tests
+
+if ($ENV{with_icu} eq 'yes')
+{
+	command_ok(['initdb', '--no-sync', '--locale-provider=icu', "$tempdir/data2"],
+			   'locale provider ICU');
+
+	command_ok(['initdb', '--no-sync', '--locale-provider=icu', '--icu-locale=en', "$tempdir/data3"],
+		'option --icu-locale');
+
+	command_fails(['initdb', '--no-sync', '--locale-provider=icu', '--icu-locale=@colNumeric=lower', "$tempdir/dataX"],
+		'fails for invalid ICU locale');
+}
+else
+{
+	command_fails(['initdb', '--no-sync', '--locale-provider=icu', "$tempdir/data2"],
+				  'locale provider ICU fails since no ICU support');
+}
+
+command_fails(['initdb', '--no-sync', '--locale-provider=xyz', "$tempdir/dataX"],
+			  'fails for invalid locale provider');
+
+command_fails(['initdb', '--no-sync', '--locale-provider=libc', '--icu-locale=en', "$tempdir/dataX"],
+			  'fails for invalid option combination');
+
 done_testing();
diff --git a/src/bin/pg_dump/pg_dump.c b/src/bin/pg_dump/pg_dump.c
index 4485ea83b1..a3d53c25c9 100644
--- a/src/bin/pg_dump/pg_dump.c
+++ b/src/bin/pg_dump/pg_dump.c
@@ -2753,8 +2753,10 @@ dumpDatabase(Archive *fout)
 				i_datname,
 				i_datdba,
 				i_encoding,
+				i_datlocprovider,
 				i_collate,
 				i_ctype,
+				i_daticulocale,
 				i_frozenxid,
 				i_minmxid,
 				i_datacl,
@@ -2769,8 +2771,10 @@ dumpDatabase(Archive *fout)
 	const char *datname,
 			   *dba,
 			   *encoding,
+			   *datlocprovider,
 			   *collate,
 			   *ctype,
+			   *iculocale,
 			   *datistemplate,
 			   *datconnlimit,
 			   *tablespace;
@@ -2794,9 +2798,9 @@ dumpDatabase(Archive *fout)
 	else
 		appendPQExpBuffer(dbQry, "0 AS datminmxid, ");
 	if (fout->remoteVersion >= 150000)
-		appendPQExpBuffer(dbQry, "datcollversion, ");
+		appendPQExpBuffer(dbQry, "datlocprovider, daticulocale, datcollversion, ");
 	else
-		appendPQExpBuffer(dbQry, "NULL AS datcollversion, ");
+		appendPQExpBuffer(dbQry, "'c' AS datlocprovider, NULL AS daticulocale, NULL AS datcollversion, ");
 	appendPQExpBuffer(dbQry,
 					  "(SELECT spcname FROM pg_tablespace t WHERE t.oid = dattablespace) AS tablespace, "
 					  "shobj_description(oid, 'pg_database') AS description "
@@ -2810,8 +2814,10 @@ dumpDatabase(Archive *fout)
 	i_datname = PQfnumber(res, "datname");
 	i_datdba = PQfnumber(res, "datdba");
 	i_encoding = PQfnumber(res, "encoding");
+	i_datlocprovider = PQfnumber(res, "datlocprovider");
 	i_collate = PQfnumber(res, "datcollate");
 	i_ctype = PQfnumber(res, "datctype");
+	i_daticulocale = PQfnumber(res, "daticulocale");
 	i_frozenxid = PQfnumber(res, "datfrozenxid");
 	i_minmxid = PQfnumber(res, "datminmxid");
 	i_datacl = PQfnumber(res, "datacl");
@@ -2826,8 +2832,13 @@ dumpDatabase(Archive *fout)
 	datname = PQgetvalue(res, 0, i_datname);
 	dba = getRoleName(PQgetvalue(res, 0, i_datdba));
 	encoding = PQgetvalue(res, 0, i_encoding);
+	datlocprovider = PQgetvalue(res, 0, i_datlocprovider);
 	collate = PQgetvalue(res, 0, i_collate);
 	ctype = PQgetvalue(res, 0, i_ctype);
+	if (!PQgetisnull(res, 0, i_daticulocale))
+		iculocale = PQgetvalue(res, 0, i_daticulocale);
+	else
+		iculocale = NULL;
 	frozenxid = atooid(PQgetvalue(res, 0, i_frozenxid));
 	minmxid = atooid(PQgetvalue(res, 0, i_minmxid));
 	dbdacl.acl = PQgetvalue(res, 0, i_datacl);
@@ -2859,6 +2870,17 @@ dumpDatabase(Archive *fout)
 		appendPQExpBufferStr(creaQry, " ENCODING = ");
 		appendStringLiteralAH(creaQry, encoding, fout);
 	}
+	if (strlen(datlocprovider) > 0)
+	{
+		appendPQExpBufferStr(creaQry, " LOCALE_PROVIDER = ");
+		if (datlocprovider[0] == 'c')
+			appendPQExpBufferStr(creaQry, "libc");
+		else if (datlocprovider[0] == 'i')
+			appendPQExpBufferStr(creaQry, "icu");
+		else
+			fatal("unrecognized locale provider: %s",
+				  datlocprovider);
+	}
 	if (strlen(collate) > 0 && strcmp(collate, ctype) == 0)
 	{
 		appendPQExpBufferStr(creaQry, " LOCALE = ");
@@ -2877,6 +2899,11 @@ dumpDatabase(Archive *fout)
 			appendStringLiteralAH(creaQry, ctype, fout);
 		}
 	}
+	if (iculocale)
+	{
+		appendPQExpBufferStr(creaQry, " ICU_LOCALE = ");
+		appendStringLiteralAH(creaQry, iculocale, fout);
+	}
 
 	/*
 	 * For binary upgrade, carry over the collation version.  For normal
diff --git a/src/bin/pg_upgrade/check.c b/src/bin/pg_upgrade/check.c
index 019bcb6c7b..cf3b398d9e 100644
--- a/src/bin/pg_upgrade/check.c
+++ b/src/bin/pg_upgrade/check.c
@@ -10,6 +10,7 @@
 #include "postgres_fe.h"
 
 #include "catalog/pg_authid_d.h"
+#include "catalog/pg_collation.h"
 #include "fe_utils/string_utils.h"
 #include "mb/pg_wchar.h"
 #include "pg_upgrade.h"
@@ -349,6 +350,18 @@ check_locale_and_encoding(DbInfo *olddb, DbInfo *newdb)
 	if (!equivalent_locale(LC_CTYPE, olddb->db_ctype, newdb->db_ctype))
 		pg_fatal("lc_ctype values for database \"%s\" do not match:  old \"%s\", new \"%s\"\n",
 				 olddb->db_name, olddb->db_ctype, newdb->db_ctype);
+	if (olddb->db_collprovider != newdb->db_collprovider)
+		pg_fatal("locale providers for database \"%s\" do not match:  old \"%s\", new \"%s\"\n",
+				 olddb->db_name,
+				 collprovider_name(olddb->db_collprovider),
+				 collprovider_name(newdb->db_collprovider));
+	if ((olddb->db_iculocale == NULL && newdb->db_iculocale != NULL) ||
+		(olddb->db_iculocale != NULL && newdb->db_iculocale == NULL) ||
+		(olddb->db_iculocale != NULL && newdb->db_iculocale != NULL && strcmp(olddb->db_iculocale, newdb->db_iculocale) != 0))
+		pg_fatal("ICU locale values for database \"%s\" do not match:  old \"%s\", new \"%s\"\n",
+				 olddb->db_name,
+				 olddb->db_iculocale ? olddb->db_iculocale : "(null)",
+				 newdb->db_iculocale ? newdb->db_iculocale : "(null)");
 }
 
 /*
diff --git a/src/bin/pg_upgrade/info.c b/src/bin/pg_upgrade/info.c
index 69ef23119f..5c3968e0ea 100644
--- a/src/bin/pg_upgrade/info.c
+++ b/src/bin/pg_upgrade/info.c
@@ -312,11 +312,20 @@ get_db_infos(ClusterInfo *cluster)
 				i_encoding,
 				i_datcollate,
 				i_datctype,
+				i_datlocprovider,
+				i_daticulocale,
 				i_spclocation;
 	char		query[QUERY_ALLOC];
 
 	snprintf(query, sizeof(query),
-			 "SELECT d.oid, d.datname, d.encoding, d.datcollate, d.datctype, "
+			 "SELECT d.oid, d.datname, d.encoding, d.datcollate, d.datctype, ");
+	if (GET_MAJOR_VERSION(old_cluster.major_version) <= 1500)
+		snprintf(query + strlen(query), sizeof(query) - strlen(query),
+				 "'c' AS datlocprovider, NULL AS daticulocale, ");
+	else
+		snprintf(query + strlen(query), sizeof(query) - strlen(query),
+				 "datlocprovider, daticulocale, ");
+	snprintf(query + strlen(query), sizeof(query) - strlen(query),
 			 "pg_catalog.pg_tablespace_location(t.oid) AS spclocation "
 			 "FROM pg_catalog.pg_database d "
 			 " LEFT OUTER JOIN pg_catalog.pg_tablespace t "
@@ -331,6 +340,8 @@ get_db_infos(ClusterInfo *cluster)
 	i_encoding = PQfnumber(res, "encoding");
 	i_datcollate = PQfnumber(res, "datcollate");
 	i_datctype = PQfnumber(res, "datctype");
+	i_datlocprovider = PQfnumber(res, "datlocprovider");
+	i_daticulocale = PQfnumber(res, "daticulocale");
 	i_spclocation = PQfnumber(res, "spclocation");
 
 	ntups = PQntuples(res);
@@ -343,6 +354,11 @@ get_db_infos(ClusterInfo *cluster)
 		dbinfos[tupnum].db_encoding = atoi(PQgetvalue(res, tupnum, i_encoding));
 		dbinfos[tupnum].db_collate = pg_strdup(PQgetvalue(res, tupnum, i_datcollate));
 		dbinfos[tupnum].db_ctype = pg_strdup(PQgetvalue(res, tupnum, i_datctype));
+		dbinfos[tupnum].db_collprovider = PQgetvalue(res, tupnum, i_datlocprovider)[0];
+		if (PQgetisnull(res, tupnum, i_daticulocale))
+			dbinfos[tupnum].db_iculocale = NULL;
+		else
+			dbinfos[tupnum].db_iculocale = pg_strdup(PQgetvalue(res, tupnum, i_daticulocale));
 		snprintf(dbinfos[tupnum].db_tablespace, sizeof(dbinfos[tupnum].db_tablespace), "%s",
 				 PQgetvalue(res, tupnum, i_spclocation));
 	}
diff --git a/src/bin/pg_upgrade/pg_upgrade.h b/src/bin/pg_upgrade/pg_upgrade.h
index 0aca0a77aa..93c31fbc21 100644
--- a/src/bin/pg_upgrade/pg_upgrade.h
+++ b/src/bin/pg_upgrade/pg_upgrade.h
@@ -171,6 +171,8 @@ typedef struct
 											 * path */
 	char	   *db_collate;
 	char	   *db_ctype;
+	char		db_collprovider;
+	char	   *db_iculocale;
 	int			db_encoding;
 	RelInfoArr	rel_arr;		/* array of all user relinfos */
 } DbInfo;
diff --git a/src/bin/psql/describe.c b/src/bin/psql/describe.c
index 654ef2d7c3..20d654e9fc 100644
--- a/src/bin/psql/describe.c
+++ b/src/bin/psql/describe.c
@@ -896,6 +896,18 @@ listAllDbs(const char *pattern, bool verbose)
 					  gettext_noop("Encoding"),
 					  gettext_noop("Collate"),
 					  gettext_noop("Ctype"));
+	if (pset.sversion >= 150000)
+		appendPQExpBuffer(&buf,
+						  "       d.daticulocale as \"%s\",\n"
+						  "       CASE d.datlocprovider WHEN 'c' THEN 'libc' WHEN 'i' THEN 'icu' END AS \"%s\",\n",
+						  gettext_noop("ICU Locale"),
+						  gettext_noop("Locale Provider"));
+	else
+		appendPQExpBuffer(&buf,
+						  "       d.datcollate as \"%s\",\n"
+						  "       'libc' AS \"%s\",\n",
+						  gettext_noop("ICU Locale"),
+						  gettext_noop("Locale Provider"));
 	appendPQExpBufferStr(&buf, "       ");
 	printACLColumn(&buf, "d.datacl");
 	if (verbose)
@@ -4614,7 +4626,7 @@ listCollations(const char *pattern, bool verbose, bool showSystem)
 	PQExpBufferData buf;
 	PGresult   *res;
 	printQueryOpt myopt = pset.popt;
-	static const bool translate_columns[] = {false, false, false, false, false, true, false};
+	static const bool translate_columns[] = {false, false, false, false, false, false, true, false};
 
 	initPQExpBuffer(&buf);
 
@@ -4628,6 +4640,15 @@ listCollations(const char *pattern, bool verbose, bool showSystem)
 					  gettext_noop("Collate"),
 					  gettext_noop("Ctype"));
 
+	if (pset.sversion >= 150000)
+		appendPQExpBuffer(&buf,
+						  ",\n       c.colliculocale AS \"%s\"",
+						  gettext_noop("ICU Locale"));
+	else
+		appendPQExpBuffer(&buf,
+						  ",\n       c.collcollate AS \"%s\"",
+						  gettext_noop("ICU Locale"));
+
 	if (pset.sversion >= 100000)
 		appendPQExpBuffer(&buf,
 						  ",\n       CASE c.collprovider WHEN 'd' THEN 'default' WHEN 'c' THEN 'libc' WHEN 'i' THEN 'icu' END AS \"%s\"",
diff --git a/src/bin/psql/tab-complete.c b/src/bin/psql/tab-complete.c
index 010edb685f..add13f7de8 100644
--- a/src/bin/psql/tab-complete.c
+++ b/src/bin/psql/tab-complete.c
@@ -2724,7 +2724,8 @@ psql_completion(const char *text, int start, int end)
 		COMPLETE_WITH("OWNER", "TEMPLATE", "ENCODING", "TABLESPACE",
 					  "IS_TEMPLATE",
 					  "ALLOW_CONNECTIONS", "CONNECTION LIMIT",
-					  "LC_COLLATE", "LC_CTYPE", "LOCALE", "OID");
+					  "LC_COLLATE", "LC_CTYPE", "LOCALE", "OID",
+					  "LOCALE_PROVIDER", "ICU_LOCALE");
 
 	else if (Matches("CREATE", "DATABASE", MatchAny, "TEMPLATE"))
 		COMPLETE_WITH_QUERY(Query_for_list_of_template_databases);
diff --git a/src/bin/scripts/Makefile b/src/bin/scripts/Makefile
index b833109da6..25e7da3d3f 100644
--- a/src/bin/scripts/Makefile
+++ b/src/bin/scripts/Makefile
@@ -53,6 +53,8 @@ clean distclean maintainer-clean:
 	rm -f common.o $(WIN32RES)
 	rm -rf tmp_check
 
+export with_icu
+
 check:
 	$(prove_check)
 
diff --git a/src/bin/scripts/createdb.c b/src/bin/scripts/createdb.c
index b0c6805bc9..6f612abf7c 100644
--- a/src/bin/scripts/createdb.c
+++ b/src/bin/scripts/createdb.c
@@ -38,6 +38,8 @@ main(int argc, char *argv[])
 		{"lc-ctype", required_argument, NULL, 2},
 		{"locale", required_argument, NULL, 'l'},
 		{"maintenance-db", required_argument, NULL, 3},
+		{"locale-provider", required_argument, NULL, 4},
+		{"icu-locale", required_argument, NULL, 5},
 		{NULL, 0, NULL, 0}
 	};
 
@@ -61,6 +63,8 @@ main(int argc, char *argv[])
 	char	   *lc_collate = NULL;
 	char	   *lc_ctype = NULL;
 	char	   *locale = NULL;
+	char	   *locale_provider = NULL;
+	char	   *icu_locale = NULL;
 
 	PQExpBufferData sql;
 
@@ -119,6 +123,12 @@ main(int argc, char *argv[])
 			case 3:
 				maintenance_db = pg_strdup(optarg);
 				break;
+			case 4:
+				locale_provider = pg_strdup(optarg);
+				break;
+			case 5:
+				icu_locale = pg_strdup(optarg);
+				break;
 			default:
 				fprintf(stderr, _("Try \"%s --help\" for more information.\n"), progname);
 				exit(1);
@@ -217,6 +227,13 @@ main(int argc, char *argv[])
 		appendPQExpBufferStr(&sql, " LC_CTYPE ");
 		appendStringLiteralConn(&sql, lc_ctype, conn);
 	}
+	if (locale_provider)
+		appendPQExpBuffer(&sql, " LOCALE_PROVIDER %s", locale_provider);
+	if (icu_locale)
+	{
+		appendPQExpBufferStr(&sql, " ICU_LOCALE ");
+		appendStringLiteralConn(&sql, icu_locale, conn);
+	}
 
 	appendPQExpBufferChar(&sql, ';');
 
@@ -273,6 +290,9 @@ help(const char *progname)
 	printf(_("  -l, --locale=LOCALE          locale settings for the database\n"));
 	printf(_("      --lc-collate=LOCALE      LC_COLLATE setting for the database\n"));
 	printf(_("      --lc-ctype=LOCALE        LC_CTYPE setting for the database\n"));
+	printf(_("      --icu-locale=LOCALE      ICU locale setting for the database\n"));
+	printf(_("      --locale-provider={libc|icu}\n"
+			 "                               locale provider for the database's default collation\n"));
 	printf(_("  -O, --owner=OWNER            database user to own the new database\n"));
 	printf(_("  -T, --template=TEMPLATE      template database to copy\n"));
 	printf(_("  -V, --version                output version information, then exit\n"));
diff --git a/src/bin/scripts/t/020_createdb.pl b/src/bin/scripts/t/020_createdb.pl
index 639245466e..35deec9a92 100644
--- a/src/bin/scripts/t/020_createdb.pl
+++ b/src/bin/scripts/t/020_createdb.pl
@@ -25,9 +25,37 @@
 	qr/statement: CREATE DATABASE foobar2 ENCODING 'LATIN1'/,
 	'create database with encoding');
 
+if ($ENV{with_icu} eq 'yes')
+{
+	# This fails because template0 uses libc provider and has no ICU
+	# locale set.  It would succeed if template0 used the icu
+	# provider.  XXX Maybe split into multiple tests?
+	$node->command_fails(
+		[ 'createdb', '-T', 'template0', '--locale-provider=icu', 'foobar4' ],
+		'create database with ICU fails without ICU locale specified');
+
+	$node->issues_sql_like(
+		[ 'createdb', '-T', 'template0', '--locale-provider=icu', '--icu-locale=en', 'foobar5' ],
+		qr/statement: CREATE DATABASE foobar5 .* LOCALE_PROVIDER icu ICU_LOCALE 'en'/,
+		'create database with ICU locale specified');
+
+	$node->command_fails(
+		[ 'createdb', '-T', 'template0', '--locale-provider=icu', '--icu-locale=@colNumeric=lower', 'foobarX' ],
+		'fails for invalid ICU locale');
+}
+else
+{
+	$node->command_fails(
+		[ 'createdb', '-T', 'template0', '--locale-provider=icu', 'foobar4' ],
+		'create database with ICU fails since no ICU support');
+}
+
 $node->command_fails([ 'createdb', 'foobar1' ],
 	'fails if database already exists');
 
+$node->command_fails([ 'createdb', '-T', 'template0', '--locale-provider=xyz', 'foobarX' ],
+	'fails for invalid locale provider');
+
 # Check use of templates with shared dependencies copied from the template.
 my ($ret, $stdout, $stderr) = $node->psql(
 	'foobar2',
diff --git a/src/include/catalog/pg_collation.dat b/src/include/catalog/pg_collation.dat
index 4b56825d82..f7470ead49 100644
--- a/src/include/catalog/pg_collation.dat
+++ b/src/include/catalog/pg_collation.dat
@@ -14,8 +14,7 @@
 
 { oid => '100', oid_symbol => 'DEFAULT_COLLATION_OID',
   descr => 'database\'s default collation',
-  collname => 'default', collprovider => 'd', collencoding => '-1',
-  collcollate => '', collctype => '' },
+  collname => 'default', collprovider => 'd', collencoding => '-1' },
 { oid => '950', oid_symbol => 'C_COLLATION_OID',
   descr => 'standard C collation',
   collname => 'C', collprovider => 'c', collencoding => '-1',
diff --git a/src/include/catalog/pg_collation.h b/src/include/catalog/pg_collation.h
index 8763dd4080..c642c3bb95 100644
--- a/src/include/catalog/pg_collation.h
+++ b/src/include/catalog/pg_collation.h
@@ -40,8 +40,9 @@ CATALOG(pg_collation,3456,CollationRelationId)
 	bool		collisdeterministic BKI_DEFAULT(t);
 	int32		collencoding;	/* encoding for this collation; -1 = "all" */
 #ifdef CATALOG_VARLEN			/* variable-length fields start here */
-	text		collcollate BKI_FORCE_NOT_NULL;		/* LC_COLLATE setting */
-	text		collctype BKI_FORCE_NOT_NULL;		/* LC_CTYPE setting */
+	text		collcollate BKI_DEFAULT(_null_);	/* LC_COLLATE setting */
+	text		collctype BKI_DEFAULT(_null_);		/* LC_CTYPE setting */
+	text		colliculocale BKI_DEFAULT(_null_);	/* ICU locale ID */
 	text		collversion BKI_DEFAULT(_null_);	/* provider-dependent
 													 * version of collation
 													 * data */
@@ -66,6 +67,20 @@ DECLARE_UNIQUE_INDEX_PKEY(pg_collation_oid_index, 3085, CollationOidIndexId, on
 #define COLLPROVIDER_ICU		'i'
 #define COLLPROVIDER_LIBC		'c'
 
+static inline const char *
+collprovider_name(char c)
+{
+	switch (c)
+	{
+		case COLLPROVIDER_ICU:
+			return "icu";
+		case COLLPROVIDER_LIBC:
+			return "libc";
+		default:
+			return "???";
+	}
+}
+
 #endif							/* EXPOSE_TO_CLIENT_CODE */
 
 
@@ -75,6 +90,7 @@ extern Oid	CollationCreate(const char *collname, Oid collnamespace,
 							bool collisdeterministic,
 							int32 collencoding,
 							const char *collcollate, const char *collctype,
+							const char *colliculocale,
 							const char *collversion,
 							bool if_not_exists,
 							bool quiet);
diff --git a/src/include/catalog/pg_database.dat b/src/include/catalog/pg_database.dat
index e7e42d6023..5feedff7bf 100644
--- a/src/include/catalog/pg_database.dat
+++ b/src/include/catalog/pg_database.dat
@@ -14,9 +14,9 @@
 
 { oid => '1', oid_symbol => 'TemplateDbOid',
   descr => 'default template for new databases',
-  datname => 'template1', encoding => 'ENCODING', datistemplate => 't',
+  datname => 'template1', encoding => 'ENCODING', datlocprovider => 'LOCALE_PROVIDER', datistemplate => 't',
   datallowconn => 't', datconnlimit => '-1', datfrozenxid => '0',
   datminmxid => '1', dattablespace => 'pg_default', datcollate => 'LC_COLLATE',
-  datctype => 'LC_CTYPE', datacl => '_null_' },
+  datctype => 'LC_CTYPE', daticulocale => 'ICU_LOCALE', datacl => '_null_' },
 
 ]
diff --git a/src/include/catalog/pg_database.h b/src/include/catalog/pg_database.h
index 76adbd4aad..a9f4a8071f 100644
--- a/src/include/catalog/pg_database.h
+++ b/src/include/catalog/pg_database.h
@@ -40,6 +40,9 @@ CATALOG(pg_database,1262,DatabaseRelationId) BKI_SHARED_RELATION BKI_ROWTYPE_OID
 	/* character encoding */
 	int32		encoding;
 
+	/* locale provider, see pg_collation.collprovider */
+	char		datlocprovider;
+
 	/* allowed as CREATE DATABASE template? */
 	bool		datistemplate;
 
@@ -65,6 +68,9 @@ CATALOG(pg_database,1262,DatabaseRelationId) BKI_SHARED_RELATION BKI_ROWTYPE_OID
 	/* LC_CTYPE setting */
 	text		datctype BKI_FORCE_NOT_NULL;
 
+	/* ICU locale ID */
+	text		daticulocale;
+
 	/* provider-dependent version of collation data */
 	text		datcollversion BKI_DEFAULT(_null_);
 
diff --git a/src/include/utils/pg_locale.h b/src/include/utils/pg_locale.h
index 30e423af0e..9b158f24a0 100644
--- a/src/include/utils/pg_locale.h
+++ b/src/include/utils/pg_locale.h
@@ -103,6 +103,11 @@ struct pg_locale_struct
 
 typedef struct pg_locale_struct *pg_locale_t;
 
+extern struct pg_locale_struct default_locale;
+
+extern void make_icu_collator(const char *iculocstr,
+							  struct pg_locale_struct *resultp);
+
 extern pg_locale_t pg_newlocale_from_collation(Oid collid);
 
 extern char *get_collation_actual_version(char collprovider, const char *collcollate);
diff --git a/src/test/regress/expected/collate.icu.utf8.out b/src/test/regress/expected/collate.icu.utf8.out
index 9699ca16cf..d4c8c6de38 100644
--- a/src/test/regress/expected/collate.icu.utf8.out
+++ b/src/test/regress/expected/collate.icu.utf8.out
@@ -1029,14 +1029,12 @@ CREATE COLLATION test0 FROM "C"; -- fail, duplicate name
 ERROR:  collation "test0" already exists
 do $$
 BEGIN
-  EXECUTE 'CREATE COLLATION test1 (provider = icu, lc_collate = ' ||
-          quote_literal(current_setting('lc_collate')) ||
-          ', lc_ctype = ' ||
-          quote_literal(current_setting('lc_ctype')) || ');';
+  EXECUTE 'CREATE COLLATION test1 (provider = icu, locale = ' ||
+          quote_literal(current_setting('lc_collate')) || ');';
 END
 $$;
-CREATE COLLATION test3 (provider = icu, lc_collate = 'en_US.utf8'); -- fail, need lc_ctype
-ERROR:  parameter "lc_ctype" must be specified
+CREATE COLLATION test3 (provider = icu, lc_collate = 'en_US.utf8'); -- fail, needs "locale"
+ERROR:  parameter "locale" must be specified
 CREATE COLLATION testx (provider = icu, locale = 'nonsense'); /* never fails with ICU */  DROP COLLATION testx;
 CREATE COLLATION test4 FROM nonsense;
 ERROR:  collation "nonsense" for encoding "UTF8" does not exist
diff --git a/src/test/regress/sql/collate.icu.utf8.sql b/src/test/regress/sql/collate.icu.utf8.sql
index 242a7ce6b7..b0ddc7db44 100644
--- a/src/test/regress/sql/collate.icu.utf8.sql
+++ b/src/test/regress/sql/collate.icu.utf8.sql
@@ -366,13 +366,11 @@ CREATE SCHEMA test_schema;
 CREATE COLLATION test0 FROM "C"; -- fail, duplicate name
 do $$
 BEGIN
-  EXECUTE 'CREATE COLLATION test1 (provider = icu, lc_collate = ' ||
-          quote_literal(current_setting('lc_collate')) ||
-          ', lc_ctype = ' ||
-          quote_literal(current_setting('lc_ctype')) || ');';
+  EXECUTE 'CREATE COLLATION test1 (provider = icu, locale = ' ||
+          quote_literal(current_setting('lc_collate')) || ');';
 END
 $$;
-CREATE COLLATION test3 (provider = icu, lc_collate = 'en_US.utf8'); -- fail, need lc_ctype
+CREATE COLLATION test3 (provider = icu, lc_collate = 'en_US.utf8'); -- fail, needs "locale"
 CREATE COLLATION testx (provider = icu, locale = 'nonsense'); /* never fails with ICU */  DROP COLLATION testx;
 
 CREATE COLLATION test4 FROM nonsense;

base-commit: 27d195a57849fbcfb2ef455d40e1901b5002b505
-- 
2.35.1

From c7b408ba646c5ee5f8c6ae84bec04ca4059ed08f Mon Sep 17 00:00:00 2001
From: Peter Eisentraut <peter@eisentraut.org>
Date: Thu, 10 Mar 2022 10:49:49 +0100
Subject: [PATCH] DefineCollation() code cleanup

Reorganize the code in DefineCollation() so that the parts using the
FROM clause and the parts not doing so are more cleanly separated.  No
functionality change intended.

Reported-by: Julien Rouhaud <rjuju123@gmail.com>
---
 src/backend/commands/collationcmds.c | 109 ++++++++++++++-------------
 1 file changed, 57 insertions(+), 52 deletions(-)

diff --git a/src/backend/commands/collationcmds.c b/src/backend/commands/collationcmds.c
index 12fc2316f9..93df1d366c 100644
--- a/src/backend/commands/collationcmds.c
+++ b/src/backend/commands/collationcmds.c
@@ -63,12 +63,11 @@ DefineCollation(ParseState *pstate, List *names, List *parameters, bool if_not_e
 	DefElem    *providerEl = NULL;
 	DefElem    *deterministicEl = NULL;
 	DefElem    *versionEl = NULL;
-	char	   *collcollate = NULL;
-	char	   *collctype = NULL;
-	char	   *collproviderstr = NULL;
-	bool		collisdeterministic = true;
-	int			collencoding = 0;
-	char		collprovider = 0;
+	char	   *collcollate;
+	char	   *collctype;
+	bool		collisdeterministic;
+	int			collencoding;
+	char		collprovider;
 	char	   *collversion = NULL;
 	Oid			newoid;
 	ObjectAddress address;
@@ -167,65 +166,71 @@ DefineCollation(ParseState *pstate, List *names, List *parameters, bool if_not_e
 					(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
 					 errmsg("collation \"default\" cannot be copied")));
 	}
-
-	if (localeEl)
+	else
 	{
-		collcollate = defGetString(localeEl);
-		collctype = defGetString(localeEl);
-	}
+		char	   *collproviderstr = NULL;
 
-	if (lccollateEl)
-		collcollate = defGetString(lccollateEl);
+		collcollate = NULL;
+		collctype = NULL;
 
-	if (lcctypeEl)
-		collctype = defGetString(lcctypeEl);
+		if (localeEl)
+		{
+			collcollate = defGetString(localeEl);
+			collctype = defGetString(localeEl);
+		}
 
-	if (providerEl)
-		collproviderstr = defGetString(providerEl);
+		if (lccollateEl)
+			collcollate = defGetString(lccollateEl);
 
-	if (deterministicEl)
-		collisdeterministic = defGetBoolean(deterministicEl);
+		if (lcctypeEl)
+			collctype = defGetString(lcctypeEl);
 
-	if (versionEl)
-		collversion = defGetString(versionEl);
+		if (providerEl)
+			collproviderstr = defGetString(providerEl);
 
-	if (collproviderstr)
-	{
-		if (pg_strcasecmp(collproviderstr, "icu") == 0)
-			collprovider = COLLPROVIDER_ICU;
-		else if (pg_strcasecmp(collproviderstr, "libc") == 0)
-			collprovider = COLLPROVIDER_LIBC;
+		if (deterministicEl)
+			collisdeterministic = defGetBoolean(deterministicEl);
+		else
+			collisdeterministic = true;
+
+		if (versionEl)
+			collversion = defGetString(versionEl);
+
+		if (collproviderstr)
+		{
+			if (pg_strcasecmp(collproviderstr, "icu") == 0)
+				collprovider = COLLPROVIDER_ICU;
+			else if (pg_strcasecmp(collproviderstr, "libc") == 0)
+				collprovider = COLLPROVIDER_LIBC;
+			else
+				ereport(ERROR,
+						(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
+						 errmsg("unrecognized collation provider: %s",
+								collproviderstr)));
+		}
 		else
+			collprovider = COLLPROVIDER_LIBC;
+
+		if (!collcollate)
 			ereport(ERROR,
 					(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
-					 errmsg("unrecognized collation provider: %s",
-							collproviderstr)));
-	}
-	else if (!fromEl)
-		collprovider = COLLPROVIDER_LIBC;
-
-	if (!collcollate)
-		ereport(ERROR,
-				(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
-				 errmsg("parameter \"lc_collate\" must be specified")));
+					 errmsg("parameter \"lc_collate\" must be specified")));
 
-	if (!collctype)
-		ereport(ERROR,
-				(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
-				 errmsg("parameter \"lc_ctype\" must be specified")));
+		if (!collctype)
+			ereport(ERROR,
+					(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
+					 errmsg("parameter \"lc_ctype\" must be specified")));
 
-	/*
-	 * Nondeterministic collations are currently only supported with ICU
-	 * because that's the only case where it can actually make a difference.
-	 * So we can save writing the code for the other providers.
-	 */
-	if (!collisdeterministic && collprovider != COLLPROVIDER_ICU)
-		ereport(ERROR,
-				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-				 errmsg("nondeterministic collations not supported with this provider")));
+		/*
+		 * Nondeterministic collations are currently only supported with ICU
+		 * because that's the only case where it can actually make a difference.
+		 * So we can save writing the code for the other providers.
+		 */
+		if (!collisdeterministic && collprovider != COLLPROVIDER_ICU)
+			ereport(ERROR,
+					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+					 errmsg("nondeterministic collations not supported with this provider")));
 
-	if (!fromEl)
-	{
 		if (collprovider == COLLPROVIDER_ICU)
 		{
 #ifdef USE_ICU
-- 
2.35.1

From 7d9703ae72a0b82168eaf8be3d8274e1101df71a Mon Sep 17 00:00:00 2001
From: Peter Eisentraut <peter@eisentraut.org>
Date: Mon, 14 Mar 2022 13:46:15 +0100
Subject: [PATCH v6] Add option to use ICU as global locale provider

This adds the option to use ICU as the default locale provider for
either the whole cluster or a database.  New options for initdb,
createdb, and CREATE DATABASE are used to select this.

Since some (legacy) code still uses the libc locale facilities
directly, we still need to set the libc global locale settings even if
ICU is otherwise selected.  So pg_database now has three
locale-related fields: the existing datcollate and datctype, which are
always set, and a new daticulocale, which is only set if ICU is
selected.  A similar change is made in pg_collation for consistency,
but in that case, only the libc-related fields or the ICU-related
field is set, never both.

Discussion: https://www.postgresql.org/message-id/flat/5e756dd6-0e91-d778-96fd-b1bcb06c161a%402ndquadrant.com

XXX catversion bump
---
 doc/src/sgml/catalogs.sgml                    |   9 +
 doc/src/sgml/ref/create_database.sgml         |  25 +++
 doc/src/sgml/ref/createdb.sgml                |  19 +++
 doc/src/sgml/ref/initdb.sgml                  |  72 ++++++--
 src/backend/catalog/pg_collation.c            |  18 +-
 src/backend/commands/collationcmds.c          |  96 +++++++----
 src/backend/commands/dbcommands.c             | 159 +++++++++++++++---
 src/backend/utils/adt/pg_locale.c             | 144 ++++++++++------
 src/backend/utils/init/postinit.c             |  21 ++-
 src/bin/initdb/Makefile                       |   4 +-
 src/bin/initdb/initdb.c                       |  97 +++++++++--
 src/bin/initdb/t/001_initdb.pl                |  27 +++
 src/bin/pg_dump/pg_dump.c                     |  30 +++-
 src/bin/pg_upgrade/check.c                    |  13 ++
 src/bin/pg_upgrade/info.c                     |  18 +-
 src/bin/pg_upgrade/pg_upgrade.h               |   2 +
 src/bin/psql/describe.c                       |  23 ++-
 src/bin/psql/tab-complete.c                   |   3 +-
 src/bin/scripts/Makefile                      |   2 +
 src/bin/scripts/createdb.c                    |  20 +++
 src/bin/scripts/t/020_createdb.pl             |  28 +++
 src/include/catalog/pg_collation.dat          |   3 +-
 src/include/catalog/pg_collation.h            |  20 ++-
 src/include/catalog/pg_database.dat           |   4 +-
 src/include/catalog/pg_database.h             |   6 +
 src/include/utils/pg_locale.h                 |   5 +
 src/test/Makefile                             |   6 +-
 src/test/icu/.gitignore                       |   2 +
 src/test/icu/Makefile                         |  25 +++
 src/test/icu/README                           |  27 +++
 src/test/icu/t/010_database.pl                |  58 +++++++
 .../regress/expected/collate.icu.utf8.out     |  10 +-
 src/test/regress/sql/collate.icu.utf8.sql     |   8 +-
 33 files changed, 837 insertions(+), 167 deletions(-)
 create mode 100644 src/test/icu/.gitignore
 create mode 100644 src/test/icu/Makefile
 create mode 100644 src/test/icu/README
 create mode 100644 src/test/icu/t/010_database.pl

diff --git a/doc/src/sgml/catalogs.sgml b/doc/src/sgml/catalogs.sgml
index 7777d60514..bcf2b43206 100644
--- a/doc/src/sgml/catalogs.sgml
+++ b/doc/src/sgml/catalogs.sgml
@@ -2384,6 +2384,15 @@ <title><structname>pg_collation</structname> Columns</title>
       </para></entry>
      </row>
 
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
+       <structfield>colliculocale</structfield> <type>text</type>
+      </para>
+      <para>
+       ICU locale ID for this collation object
+      </para></entry>
+     </row>
+
      <row>
       <entry role="catalog_table_entry"><para role="column_definition">
        <structfield>collversion</structfield> <type>text</type>
diff --git a/doc/src/sgml/ref/create_database.sgml b/doc/src/sgml/ref/create_database.sgml
index f70d0c75b4..33e2d7ce83 100644
--- a/doc/src/sgml/ref/create_database.sgml
+++ b/doc/src/sgml/ref/create_database.sgml
@@ -28,6 +28,8 @@
            [ LOCALE [=] <replaceable class="parameter">locale</replaceable> ]
            [ LC_COLLATE [=] <replaceable class="parameter">lc_collate</replaceable> ]
            [ LC_CTYPE [=] <replaceable class="parameter">lc_ctype</replaceable> ]
+           [ ICU_LOCALE [=] <replaceable class="parameter">icu_locale</replaceable> ]
+           [ LOCALE_PROVIDER [=] <replaceable class="parameter">locale_provider</replaceable> ]
            [ COLLATION_VERSION = <replaceable>collation_version</replaceable> ]
            [ TABLESPACE [=] <replaceable class="parameter">tablespace_name</replaceable> ]
            [ ALLOW_CONNECTIONS [=] <replaceable class="parameter">allowconn</replaceable> ]
@@ -160,6 +162,29 @@ <title>Parameters</title>
       </listitem>
      </varlistentry>
 
+     <varlistentry>
+      <term><replaceable class="parameter">icu_locale</replaceable></term>
+      <listitem>
+       <para>
+        Specifies the ICU locale ID if the ICU locale provider is used.
+       </para>
+      </listitem>
+     </varlistentry>
+
+     <varlistentry>
+      <term><replaceable>locale_provider</replaceable></term>
+
+      <listitem>
+       <para>
+        Specifies the provider to use for the default collation in this
+        database.  Possible values are:
+        <literal>icu</literal>,<indexterm><primary>ICU</primary></indexterm>
+        <literal>libc</literal>.  <literal>libc</literal> is the default.  The
+        available choices depend on the operating system and build options.
+       </para>
+      </listitem>
+     </varlistentry>
+
      <varlistentry>
       <term><replaceable>collation_version</replaceable></term>
 
diff --git a/doc/src/sgml/ref/createdb.sgml b/doc/src/sgml/ref/createdb.sgml
index 86473455c9..be42e502d6 100644
--- a/doc/src/sgml/ref/createdb.sgml
+++ b/doc/src/sgml/ref/createdb.sgml
@@ -147,6 +147,25 @@ <title>Options</title>
       </listitem>
      </varlistentry>
 
+     <varlistentry>
+      <term><option>--icu-locale=<replaceable class="parameter">locale</replaceable></option></term>
+      <listitem>
+       <para>
+        Specifies the ICU locale ID to be used in this database, if the
+        ICU locale provider is selected.
+       </para>
+      </listitem>
+     </varlistentry>
+
+     <varlistentry>
+      <term><option>--locale-provider={<literal>libc</literal>|<literal>icu</literal>}</option></term>
+      <listitem>
+       <para>
+        Specifies the locale provider for the database's default collation.
+       </para>
+      </listitem>
+     </varlistentry>
+
      <varlistentry>
       <term><option>-O <replaceable class="parameter">owner</replaceable></option></term>
       <term><option>--owner=<replaceable class="parameter">owner</replaceable></option></term>
diff --git a/doc/src/sgml/ref/initdb.sgml b/doc/src/sgml/ref/initdb.sgml
index 8f71c7c962..f5d633b0af 100644
--- a/doc/src/sgml/ref/initdb.sgml
+++ b/doc/src/sgml/ref/initdb.sgml
@@ -86,30 +86,45 @@ <title>Description</title>
   </para>
 
   <para>
-   <command>initdb</command> initializes the database cluster's default
-   locale and character set encoding. The character set encoding,
-   collation order (<literal>LC_COLLATE</literal>) and character set classes
-   (<literal>LC_CTYPE</literal>, e.g., upper, lower, digit) can be set separately
-   for a database when it is created. <command>initdb</command> determines
-   those settings for the template databases, which will
-   serve as the default for all other databases.
+   <command>initdb</command> initializes the database cluster's default locale
+   and character set encoding. These can also be set separately for each
+   database when it is created. <command>initdb</command> determines those
+   settings for the template databases, which will serve as the default for
+   all other databases.  By default, <command>initdb</command> uses the
+   locale provider <literal>libc</literal>, takes the locale settings from
+   the environment, and determines the encoding from the locale settings.
+   This is almost always sufficient, unless there are special requirements.
   </para>
 
   <para>
-   To alter the default collation order or character set classes, use the
-   <option>--lc-collate</option> and <option>--lc-ctype</option> options.
-   Collation orders other than <literal>C</literal> or <literal>POSIX</literal> also have
-   a performance penalty.  For these reasons it is important to choose the
-   right locale when running <command>initdb</command>.
+   To choose a different locale for the cluster, use the option
+   <option>--locale</option>.  There are also individual options
+   <option>--lc-*</option> (see below) to set values for the individual locale
+   categories.  Note that inconsistent settings for different locale
+   categories can give nonsensical results, so this should be used with care.
   </para>
 
   <para>
-   The remaining locale categories can be changed later when the server
-   is started.  You can also use <option>--locale</option> to set the
-   default for all locale categories, including collation order and
-   character set classes. All server locale values (<literal>lc_*</literal>) can
-   be displayed via <command>SHOW ALL</command>.
-   More details can be found in <xref linkend="locale"/>.
+   Alternatively, the ICU library can be used to provide locale services.
+   (Again, this only sets the default for subsequently created databases.)  To
+   select this option, specify <literal>--locale-provider=icu</literal>.
+   To chose the specific ICU locale ID to apply, use the option
+   <option>--icu-locale</option>.  Note that
+   for implementation reasons and to support legacy code,
+   <command>initdb</command> will still select and initialize libc locale
+   settings when the ICU locale provider is used.
+  </para>
+
+  <para>
+   When <command>initdb</command> runs, it will print out the locale settings
+   it has chosen.  If you have complex requirements or specified multiple
+   options, it is advisable to check that the result matches what was
+   intended.
+  </para>
+
+  <para>
+   More details about locale settings can be found in <xref
+   linkend="locale"/>.
   </para>
 
   <para>
@@ -210,6 +225,15 @@ <title>Options</title>
       </listitem>
      </varlistentry>
 
+     <varlistentry>
+      <term><option>--icu-locale=<replaceable>locale</replaceable></option></term>
+      <listitem>
+       <para>
+        Specifies the ICU locale ID, if the ICU locale provider is used.
+       </para>
+      </listitem>
+     </varlistentry>
+
      <varlistentry id="app-initdb-data-checksums" xreflabel="data checksums">
       <term><option>-k</option></term>
       <term><option>--data-checksums</option></term>
@@ -264,6 +288,18 @@ <title>Options</title>
       </listitem>
      </varlistentry>
 
+     <varlistentry>
+      <term><option>--locale-provider={<literal>libc</literal>|<literal>icu</literal>}</option></term>
+      <listitem>
+       <para>
+        This option sets the locale provider for databases created in the
+        new cluster.  It can be overridden in the <command>CREATE
+        DATABASE</command> command when new databases are subsequently
+        created.  The default is <literal>libc</literal>.
+       </para>
+      </listitem>
+     </varlistentry>
+
      <varlistentry>
       <term><option>-N</option></term>
       <term><option>--no-sync</option></term>
diff --git a/src/backend/catalog/pg_collation.c b/src/backend/catalog/pg_collation.c
index bfc02d3038..93545786df 100644
--- a/src/backend/catalog/pg_collation.c
+++ b/src/backend/catalog/pg_collation.c
@@ -49,6 +49,7 @@ CollationCreate(const char *collname, Oid collnamespace,
 				bool collisdeterministic,
 				int32 collencoding,
 				const char *collcollate, const char *collctype,
+				const char *colliculocale,
 				const char *collversion,
 				bool if_not_exists,
 				bool quiet)
@@ -66,8 +67,7 @@ CollationCreate(const char *collname, Oid collnamespace,
 	AssertArg(collname);
 	AssertArg(collnamespace);
 	AssertArg(collowner);
-	AssertArg(collcollate);
-	AssertArg(collctype);
+	AssertArg((collcollate && collctype) || colliculocale);
 
 	/*
 	 * Make sure there is no existing collation of same name & encoding.
@@ -161,8 +161,18 @@ CollationCreate(const char *collname, Oid collnamespace,
 	values[Anum_pg_collation_collprovider - 1] = CharGetDatum(collprovider);
 	values[Anum_pg_collation_collisdeterministic - 1] = BoolGetDatum(collisdeterministic);
 	values[Anum_pg_collation_collencoding - 1] = Int32GetDatum(collencoding);
-	values[Anum_pg_collation_collcollate - 1] = CStringGetTextDatum(collcollate);
-	values[Anum_pg_collation_collctype - 1] = CStringGetTextDatum(collctype);
+	if (collcollate)
+		values[Anum_pg_collation_collcollate - 1] = CStringGetTextDatum(collcollate);
+	else
+		nulls[Anum_pg_collation_collcollate - 1] = true;
+	if (collctype)
+		values[Anum_pg_collation_collctype - 1] = CStringGetTextDatum(collctype);
+	else
+		nulls[Anum_pg_collation_collctype - 1] = true;
+	if (colliculocale)
+		values[Anum_pg_collation_colliculocale - 1] = CStringGetTextDatum(colliculocale);
+	else
+		nulls[Anum_pg_collation_colliculocale - 1] = true;
 	if (collversion)
 		values[Anum_pg_collation_collversion - 1] = CStringGetTextDatum(collversion);
 	else
diff --git a/src/backend/commands/collationcmds.c b/src/backend/commands/collationcmds.c
index 93df1d366c..b86684a833 100644
--- a/src/backend/commands/collationcmds.c
+++ b/src/backend/commands/collationcmds.c
@@ -65,6 +65,7 @@ DefineCollation(ParseState *pstate, List *names, List *parameters, bool if_not_e
 	DefElem    *versionEl = NULL;
 	char	   *collcollate;
 	char	   *collctype;
+	char	   *colliculocale;
 	bool		collisdeterministic;
 	int			collencoding;
 	char		collprovider;
@@ -152,6 +153,12 @@ DefineCollation(ParseState *pstate, List *names, List *parameters, bool if_not_e
 		else
 			collctype = NULL;
 
+		datum = SysCacheGetAttr(COLLOID, tp, Anum_pg_collation_colliculocale, &isnull);
+		if (!isnull)
+			colliculocale = TextDatumGetCString(datum);
+		else
+			colliculocale = NULL;
+
 		ReleaseSysCache(tp);
 
 		/*
@@ -172,18 +179,7 @@ DefineCollation(ParseState *pstate, List *names, List *parameters, bool if_not_e
 
 		collcollate = NULL;
 		collctype = NULL;
-
-		if (localeEl)
-		{
-			collcollate = defGetString(localeEl);
-			collctype = defGetString(localeEl);
-		}
-
-		if (lccollateEl)
-			collcollate = defGetString(lccollateEl);
-
-		if (lcctypeEl)
-			collctype = defGetString(lcctypeEl);
+		colliculocale = NULL;
 
 		if (providerEl)
 			collproviderstr = defGetString(providerEl);
@@ -211,15 +207,42 @@ DefineCollation(ParseState *pstate, List *names, List *parameters, bool if_not_e
 		else
 			collprovider = COLLPROVIDER_LIBC;
 
-		if (!collcollate)
-			ereport(ERROR,
-					(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
-					 errmsg("parameter \"lc_collate\" must be specified")));
+		if (localeEl)
+		{
+			if (collprovider == COLLPROVIDER_LIBC)
+			{
+				collcollate = defGetString(localeEl);
+				collctype = defGetString(localeEl);
+			}
+			else
+				colliculocale = defGetString(localeEl);
+		}
 
-		if (!collctype)
-			ereport(ERROR,
-					(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
-					 errmsg("parameter \"lc_ctype\" must be specified")));
+		if (lccollateEl)
+			collcollate = defGetString(lccollateEl);
+
+		if (lcctypeEl)
+			collctype = defGetString(lcctypeEl);
+
+		if (collprovider == COLLPROVIDER_LIBC)
+		{
+			if (!collcollate)
+				ereport(ERROR,
+						(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
+						 errmsg("parameter \"lc_collate\" must be specified")));
+
+			if (!collctype)
+				ereport(ERROR,
+						(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
+						 errmsg("parameter \"lc_ctype\" must be specified")));
+		}
+		else if (collprovider == COLLPROVIDER_ICU)
+		{
+			if (!colliculocale)
+				ereport(ERROR,
+						(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
+						 errmsg("parameter \"locale\" must be specified")));
+		}
 
 		/*
 		 * Nondeterministic collations are currently only supported with ICU
@@ -260,7 +283,7 @@ DefineCollation(ParseState *pstate, List *names, List *parameters, bool if_not_e
 	}
 
 	if (!collversion)
-		collversion = get_collation_actual_version(collprovider, collcollate);
+		collversion = get_collation_actual_version(collprovider, collprovider == COLLPROVIDER_ICU ? colliculocale : collcollate);
 
 	newoid = CollationCreate(collName,
 							 collNamespace,
@@ -270,6 +293,7 @@ DefineCollation(ParseState *pstate, List *names, List *parameters, bool if_not_e
 							 collencoding,
 							 collcollate,
 							 collctype,
+							 colliculocale,
 							 collversion,
 							 if_not_exists,
 							 false);	/* not quiet */
@@ -352,9 +376,11 @@ AlterCollation(AlterCollationStmt *stmt)
 	datum = SysCacheGetAttr(COLLOID, tup, Anum_pg_collation_collversion, &isnull);
 	oldversion = isnull ? NULL : TextDatumGetCString(datum);
 
-	datum = SysCacheGetAttr(COLLOID, tup, Anum_pg_collation_collcollate, &isnull);
-	Assert(!isnull);
-	newversion = get_collation_actual_version(collForm->collprovider, TextDatumGetCString(datum));
+	datum = SysCacheGetAttr(COLLOID, tup, collForm->collprovider == COLLPROVIDER_ICU ? Anum_pg_collation_colliculocale : Anum_pg_collation_collcollate, &isnull);
+	if (!isnull)
+		newversion = get_collation_actual_version(collForm->collprovider, TextDatumGetCString(datum));
+	else
+		newversion = NULL;
 
 	/* cannot change from NULL to non-NULL or vice versa */
 	if ((!oldversion && newversion) || (oldversion && !newversion))
@@ -414,9 +440,11 @@ pg_collation_actual_version(PG_FUNCTION_ARGS)
 
 	collprovider = ((Form_pg_collation) GETSTRUCT(tp))->collprovider;
 
-	datum = SysCacheGetAttr(COLLOID, tp, Anum_pg_collation_collcollate, &isnull);
-	Assert(!isnull);
-	version = get_collation_actual_version(collprovider, TextDatumGetCString(datum));
+	datum = SysCacheGetAttr(COLLOID, tp, collprovider == COLLPROVIDER_ICU ? Anum_pg_collation_colliculocale : Anum_pg_collation_collcollate, &isnull);
+	if (!isnull)
+		version = get_collation_actual_version(collprovider, TextDatumGetCString(datum));
+	else
+		version = NULL;
 
 	ReleaseSysCache(tp);
 
@@ -643,7 +671,7 @@ pg_import_system_collations(PG_FUNCTION_ARGS)
 			 */
 			collid = CollationCreate(localebuf, nspid, GetUserId(),
 									 COLLPROVIDER_LIBC, true, enc,
-									 localebuf, localebuf,
+									 localebuf, localebuf, NULL,
 									 get_collation_actual_version(COLLPROVIDER_LIBC, localebuf),
 									 true, true);
 			if (OidIsValid(collid))
@@ -704,7 +732,7 @@ pg_import_system_collations(PG_FUNCTION_ARGS)
 
 			collid = CollationCreate(alias, nspid, GetUserId(),
 									 COLLPROVIDER_LIBC, true, enc,
-									 locale, locale,
+									 locale, locale, NULL,
 									 get_collation_actual_version(COLLPROVIDER_LIBC, locale),
 									 true, true);
 			if (OidIsValid(collid))
@@ -745,7 +773,7 @@ pg_import_system_collations(PG_FUNCTION_ARGS)
 			const char *name;
 			char	   *langtag;
 			char	   *icucomment;
-			const char *collcollate;
+			const char *iculocstr;
 			Oid			collid;
 
 			if (i == -1)
@@ -754,20 +782,20 @@ pg_import_system_collations(PG_FUNCTION_ARGS)
 				name = uloc_getAvailable(i);
 
 			langtag = get_icu_language_tag(name);
-			collcollate = U_ICU_VERSION_MAJOR_NUM >= 54 ? langtag : name;
+			iculocstr = U_ICU_VERSION_MAJOR_NUM >= 54 ? langtag : name;
 
 			/*
 			 * Be paranoid about not allowing any non-ASCII strings into
 			 * pg_collation
 			 */
-			if (!pg_is_ascii(langtag) || !pg_is_ascii(collcollate))
+			if (!pg_is_ascii(langtag) || !pg_is_ascii(iculocstr))
 				continue;
 
 			collid = CollationCreate(psprintf("%s-x-icu", langtag),
 									 nspid, GetUserId(),
 									 COLLPROVIDER_ICU, true, -1,
-									 collcollate, collcollate,
-									 get_collation_actual_version(COLLPROVIDER_ICU, collcollate),
+									 NULL, NULL, iculocstr,
+									 get_collation_actual_version(COLLPROVIDER_ICU, iculocstr),
 									 true, true);
 			if (OidIsValid(collid))
 			{
diff --git a/src/backend/commands/dbcommands.c b/src/backend/commands/dbcommands.c
index c37e3c9a9a..f0b57fd69a 100644
--- a/src/backend/commands/dbcommands.c
+++ b/src/backend/commands/dbcommands.c
@@ -86,7 +86,8 @@ static bool get_db_info(const char *name, LOCKMODE lockmode,
 						Oid *dbIdP, Oid *ownerIdP,
 						int *encodingP, bool *dbIsTemplateP, bool *dbAllowConnP,
 						TransactionId *dbFrozenXidP, MultiXactId *dbMinMultiP,
-						Oid *dbTablespace, char **dbCollate, char **dbCtype,
+						Oid *dbTablespace, char **dbCollate, char **dbCtype, char **dbIculocale,
+						char *dbLocProvider,
 						char **dbCollversion);
 static bool have_createdb_privilege(void);
 static void remove_dbtablespaces(Oid db_id);
@@ -107,6 +108,8 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 	int			src_encoding = -1;
 	char	   *src_collate = NULL;
 	char	   *src_ctype = NULL;
+	char	   *src_iculocale = NULL;
+	char		src_locprovider;
 	char	   *src_collversion = NULL;
 	bool		src_istemplate;
 	bool		src_allowconn;
@@ -128,6 +131,8 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 	DefElem    *dlocale = NULL;
 	DefElem    *dcollate = NULL;
 	DefElem    *dctype = NULL;
+	DefElem    *diculocale = NULL;
+	DefElem	   *dlocprovider = NULL;
 	DefElem    *distemplate = NULL;
 	DefElem    *dallowconnections = NULL;
 	DefElem    *dconnlimit = NULL;
@@ -137,6 +142,8 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 	const char *dbtemplate = NULL;
 	char	   *dbcollate = NULL;
 	char	   *dbctype = NULL;
+	char	   *dbiculocale = NULL;
+	char		dblocprovider = '\0';
 	char	   *canonname;
 	int			encoding = -1;
 	bool		dbistemplate = false;
@@ -194,6 +201,18 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 				errorConflictingDefElem(defel, pstate);
 			dctype = defel;
 		}
+		else if (strcmp(defel->defname, "icu_locale") == 0)
+		{
+			if (diculocale)
+				errorConflictingDefElem(defel, pstate);
+			diculocale = defel;
+		}
+		else if (strcmp(defel->defname, "locale_provider") == 0)
+		{
+			if (dlocprovider)
+				errorConflictingDefElem(defel, pstate);
+			dlocprovider = defel;
+		}
 		else if (strcmp(defel->defname, "is_template") == 0)
 		{
 			if (distemplate)
@@ -257,12 +276,6 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 					 parser_errposition(pstate, defel->location)));
 	}
 
-	if (dlocale && (dcollate || dctype))
-		ereport(ERROR,
-				(errcode(ERRCODE_SYNTAX_ERROR),
-				 errmsg("conflicting or redundant options"),
-				 errdetail("LOCALE cannot be specified together with LC_COLLATE or LC_CTYPE.")));
-
 	if (downer && downer->arg)
 		dbowner = defGetString(downer);
 	if (dtemplate && dtemplate->arg)
@@ -304,6 +317,31 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 		dbcollate = defGetString(dcollate);
 	if (dctype && dctype->arg)
 		dbctype = defGetString(dctype);
+	if (diculocale && diculocale->arg)
+		dbiculocale = defGetString(diculocale);
+	if (dlocprovider && dlocprovider->arg)
+	{
+		char	   *locproviderstr = defGetString(dlocprovider);
+
+		if (pg_strcasecmp(locproviderstr, "icu") == 0)
+			dblocprovider = COLLPROVIDER_ICU;
+		else if (pg_strcasecmp(locproviderstr, "libc") == 0)
+			dblocprovider = COLLPROVIDER_LIBC;
+		else
+			ereport(ERROR,
+					(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
+					 errmsg("unrecognized locale provider: %s",
+							locproviderstr)));
+	}
+	if (diculocale && dblocprovider != COLLPROVIDER_ICU)
+		ereport(ERROR,
+				(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
+				 errmsg("ICU locale cannot be specified unless locale provider is ICU")));
+	if (dblocprovider == COLLPROVIDER_ICU && !dbiculocale)
+	{
+		if (dlocale && dlocale->arg)
+			dbiculocale = defGetString(dlocale);
+	}
 	if (distemplate && distemplate->arg)
 		dbistemplate = defGetBoolean(distemplate);
 	if (dallowconnections && dallowconnections->arg)
@@ -355,7 +393,8 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 					 &src_dboid, &src_owner, &src_encoding,
 					 &src_istemplate, &src_allowconn,
 					 &src_frozenxid, &src_minmxid, &src_deftablespace,
-					 &src_collate, &src_ctype, &src_collversion))
+					 &src_collate, &src_ctype, &src_iculocale, &src_locprovider,
+					 &src_collversion))
 		ereport(ERROR,
 				(errcode(ERRCODE_UNDEFINED_DATABASE),
 				 errmsg("template database \"%s\" does not exist",
@@ -381,6 +420,10 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 		dbcollate = src_collate;
 	if (dbctype == NULL)
 		dbctype = src_ctype;
+	if (dbiculocale == NULL)
+		dbiculocale = src_iculocale;
+	if (dblocprovider == '\0')
+		dblocprovider = src_locprovider;
 
 	/* Some encodings are client only */
 	if (!PG_VALID_BE_ENCODING(encoding))
@@ -402,6 +445,37 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 
 	check_encoding_locale_matches(encoding, dbcollate, dbctype);
 
+	if (dblocprovider == COLLPROVIDER_ICU)
+	{
+		/*
+		 * This would happen if template0 uses the libc provider but the new
+		 * database uses icu.
+		 */
+		if (!dbiculocale)
+			ereport(ERROR,
+					(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+					 errmsg("ICU locale must be specified")));
+	}
+
+	if (dblocprovider == COLLPROVIDER_ICU)
+	{
+#ifdef USE_ICU
+		UErrorCode  status;
+
+		status = U_ZERO_ERROR;
+		ucol_open(dbiculocale, &status);
+		if (U_FAILURE(status))
+			ereport(ERROR,
+					(errmsg("could not open collator for locale \"%s\": %s",
+							dbiculocale, u_errorName(status))));
+#else
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				 errmsg("ICU is not supported in this build"), \
+				 errhint("You need to rebuild PostgreSQL using %s.", "--with-icu")));
+#endif
+	}
+
 	/*
 	 * Check that the new encoding and locale settings match the source
 	 * database.  We insist on this because we simply copy the source data ---
@@ -435,6 +509,25 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 					 errmsg("new LC_CTYPE (%s) is incompatible with the LC_CTYPE of the template database (%s)",
 							dbctype, src_ctype),
 					 errhint("Use the same LC_CTYPE as in the template database, or use template0 as template.")));
+
+		if (dblocprovider != src_locprovider)
+			ereport(ERROR,
+					(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+					 errmsg("new locale provider (%s) does not match locale provider of the template database (%s)",
+							collprovider_name(dblocprovider), collprovider_name(src_locprovider)),
+					 errhint("Use the same locale provider as in the template database, or use template0 as template.")));
+
+		if (dblocprovider == COLLPROVIDER_ICU)
+		{
+			Assert(dbiculocale);
+			Assert(src_iculocale);
+			if (strcmp(dbiculocale, src_iculocale) != 0)
+				ereport(ERROR,
+						(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+						 errmsg("new ICU locale (%s) is incompatible with the ICU locale of the template database (%s)",
+								dbiculocale, src_iculocale),
+						 errhint("Use the same ICU locale as in the template database, or use template0 as template.")));
+		}
 	}
 
 	/*
@@ -453,7 +546,7 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 	{
 		char	   *actual_versionstr;
 
-		actual_versionstr = get_collation_actual_version(COLLPROVIDER_LIBC, dbcollate);
+		actual_versionstr = get_collation_actual_version(dblocprovider, dblocprovider == COLLPROVIDER_ICU ? dbiculocale : dbcollate);
 		if (!actual_versionstr)
 			ereport(ERROR,
 					(errmsg("template database \"%s\" has a collation version, but no actual collation version could be determined",
@@ -481,7 +574,7 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 	 * collation version, which is normally only the case for template0.
 	 */
 	if (dbcollversion == NULL)
-		dbcollversion = get_collation_actual_version(COLLPROVIDER_LIBC, dbcollate);
+		dbcollversion = get_collation_actual_version(dblocprovider, dblocprovider == COLLPROVIDER_ICU ? dbiculocale : dbcollate);
 
 	/* Resolve default tablespace for new database */
 	if (dtablespacename && dtablespacename->arg)
@@ -620,6 +713,9 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 	 * block on the unique index, and fail after we commit).
 	 */
 
+	Assert((dblocprovider == COLLPROVIDER_ICU && dbiculocale) ||
+		   (dblocprovider != COLLPROVIDER_ICU && !dbiculocale));
+
 	/* Form tuple */
 	MemSet(new_record, 0, sizeof(new_record));
 	MemSet(new_record_nulls, false, sizeof(new_record_nulls));
@@ -629,6 +725,7 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 		DirectFunctionCall1(namein, CStringGetDatum(dbname));
 	new_record[Anum_pg_database_datdba - 1] = ObjectIdGetDatum(datdba);
 	new_record[Anum_pg_database_encoding - 1] = Int32GetDatum(encoding);
+	new_record[Anum_pg_database_datlocprovider - 1] = CharGetDatum(dblocprovider);
 	new_record[Anum_pg_database_datistemplate - 1] = BoolGetDatum(dbistemplate);
 	new_record[Anum_pg_database_datallowconn - 1] = BoolGetDatum(dballowconnections);
 	new_record[Anum_pg_database_datconnlimit - 1] = Int32GetDatum(dbconnlimit);
@@ -637,6 +734,10 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 	new_record[Anum_pg_database_dattablespace - 1] = ObjectIdGetDatum(dst_deftablespace);
 	new_record[Anum_pg_database_datcollate - 1] = CStringGetTextDatum(dbcollate);
 	new_record[Anum_pg_database_datctype - 1] = CStringGetTextDatum(dbctype);
+	if (dbiculocale)
+		new_record[Anum_pg_database_daticulocale - 1] = CStringGetTextDatum(dbiculocale);
+	else
+		new_record_nulls[Anum_pg_database_daticulocale - 1] = true;
 	if (dbcollversion)
 		new_record[Anum_pg_database_datcollversion - 1] = CStringGetTextDatum(dbcollversion);
 	else
@@ -907,7 +1008,7 @@ dropdb(const char *dbname, bool missing_ok, bool force)
 	pgdbrel = table_open(DatabaseRelationId, RowExclusiveLock);
 
 	if (!get_db_info(dbname, AccessExclusiveLock, &db_id, NULL, NULL,
-					 &db_istemplate, NULL, NULL, NULL, NULL, NULL, NULL, NULL))
+					 &db_istemplate, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL))
 	{
 		if (!missing_ok)
 		{
@@ -1109,7 +1210,7 @@ RenameDatabase(const char *oldname, const char *newname)
 	rel = table_open(DatabaseRelationId, RowExclusiveLock);
 
 	if (!get_db_info(oldname, AccessExclusiveLock, &db_id, NULL, NULL,
-					 NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL))
+					 NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL))
 		ereport(ERROR,
 				(errcode(ERRCODE_UNDEFINED_DATABASE),
 				 errmsg("database \"%s\" does not exist", oldname)));
@@ -1222,7 +1323,7 @@ movedb(const char *dbname, const char *tblspcname)
 	pgdbrel = table_open(DatabaseRelationId, RowExclusiveLock);
 
 	if (!get_db_info(dbname, AccessExclusiveLock, &db_id, NULL, NULL,
-					 NULL, NULL, NULL, NULL, &src_tblspcoid, NULL, NULL, NULL))
+					 NULL, NULL, NULL, NULL, &src_tblspcoid, NULL, NULL, NULL, NULL, NULL))
 		ereport(ERROR,
 				(errcode(ERRCODE_UNDEFINED_DATABASE),
 				 errmsg("database \"%s\" does not exist", dbname)));
@@ -1755,9 +1856,11 @@ AlterDatabaseRefreshColl(AlterDatabaseRefreshCollStmt *stmt)
 	datum = heap_getattr(tuple, Anum_pg_database_datcollversion, RelationGetDescr(rel), &isnull);
 	oldversion = isnull ? NULL : TextDatumGetCString(datum);
 
-	datum = heap_getattr(tuple, Anum_pg_database_datcollate, RelationGetDescr(rel), &isnull);
-	Assert(!isnull);
-	newversion = get_collation_actual_version(COLLPROVIDER_LIBC, TextDatumGetCString(datum));
+	datum = heap_getattr(tuple, datForm->datlocprovider == COLLPROVIDER_ICU ? Anum_pg_database_daticulocale : Anum_pg_database_datcollate, RelationGetDescr(rel), &isnull);
+	if (!isnull)
+		newversion = get_collation_actual_version(datForm->datlocprovider, TextDatumGetCString(datum));
+	else
+		newversion = NULL;
 
 	/* cannot change from NULL to non-NULL or vice versa */
 	if ((!oldversion && newversion) || (oldversion && !newversion))
@@ -1943,6 +2046,7 @@ pg_database_collation_actual_version(PG_FUNCTION_ARGS)
 {
 	Oid			dbid = PG_GETARG_OID(0);
 	HeapTuple	tp;
+	char		datlocprovider;
 	Datum		datum;
 	bool		isnull;
 	char	   *version;
@@ -1953,9 +2057,13 @@ pg_database_collation_actual_version(PG_FUNCTION_ARGS)
 				(errcode(ERRCODE_UNDEFINED_OBJECT),
 				 errmsg("database with OID %u does not exist", dbid)));
 
-	datum = SysCacheGetAttr(DATABASEOID, tp, Anum_pg_database_datcollate, &isnull);
-	Assert(!isnull);
-	version = get_collation_actual_version(COLLPROVIDER_LIBC, TextDatumGetCString(datum));
+	datlocprovider = ((Form_pg_database) GETSTRUCT(tp))->datlocprovider;
+
+	datum = SysCacheGetAttr(DATABASEOID, tp, datlocprovider == COLLPROVIDER_ICU ? Anum_pg_database_daticulocale : Anum_pg_database_datcollate, &isnull);
+	if (!isnull)
+		version = get_collation_actual_version(datlocprovider, TextDatumGetCString(datum));
+	else
+		version = NULL;
 
 	ReleaseSysCache(tp);
 
@@ -1981,7 +2089,8 @@ get_db_info(const char *name, LOCKMODE lockmode,
 			Oid *dbIdP, Oid *ownerIdP,
 			int *encodingP, bool *dbIsTemplateP, bool *dbAllowConnP,
 			TransactionId *dbFrozenXidP, MultiXactId *dbMinMultiP,
-			Oid *dbTablespace, char **dbCollate, char **dbCtype,
+			Oid *dbTablespace, char **dbCollate, char **dbCtype, char **dbIculocale,
+			char *dbLocProvider,
 			char **dbCollversion)
 {
 	bool		result = false;
@@ -2075,6 +2184,8 @@ get_db_info(const char *name, LOCKMODE lockmode,
 				if (dbTablespace)
 					*dbTablespace = dbform->dattablespace;
 				/* default locale settings for this database */
+				if (dbLocProvider)
+					*dbLocProvider = dbform->datlocprovider;
 				if (dbCollate)
 				{
 					datum = SysCacheGetAttr(DATABASEOID, tuple, Anum_pg_database_datcollate, &isnull);
@@ -2087,6 +2198,14 @@ get_db_info(const char *name, LOCKMODE lockmode,
 					Assert(!isnull);
 					*dbCtype = TextDatumGetCString(datum);
 				}
+				if (dbIculocale)
+				{
+					datum = SysCacheGetAttr(DATABASEOID, tuple, Anum_pg_database_daticulocale, &isnull);
+					if (isnull)
+						*dbIculocale = NULL;
+					else
+						*dbIculocale = TextDatumGetCString(datum);
+				}
 				if (dbCollversion)
 				{
 					datum = SysCacheGetAttr(DATABASEOID, tuple, Anum_pg_database_datcollversion, &isnull);
diff --git a/src/backend/utils/adt/pg_locale.c b/src/backend/utils/adt/pg_locale.c
index 871a710967..4019255f8e 100644
--- a/src/backend/utils/adt/pg_locale.c
+++ b/src/backend/utils/adt/pg_locale.c
@@ -1288,26 +1288,37 @@ lookup_collation_cache(Oid collation, bool set_flags)
 	{
 		/* Attempt to set the flags */
 		HeapTuple	tp;
-		Datum		datum;
-		bool		isnull;
-		const char *collcollate;
-		const char *collctype;
+		Form_pg_collation collform;
 
 		tp = SearchSysCache1(COLLOID, ObjectIdGetDatum(collation));
 		if (!HeapTupleIsValid(tp))
 			elog(ERROR, "cache lookup failed for collation %u", collation);
+		collform = (Form_pg_collation) GETSTRUCT(tp);
 
-		datum = SysCacheGetAttr(COLLOID, tp, Anum_pg_collation_collcollate, &isnull);
-		Assert(!isnull);
-		collcollate = TextDatumGetCString(datum);
-		datum = SysCacheGetAttr(COLLOID, tp, Anum_pg_collation_collctype, &isnull);
-		Assert(!isnull);
-		collctype = TextDatumGetCString(datum);
-
-		cache_entry->collate_is_c = ((strcmp(collcollate, "C") == 0) ||
-									 (strcmp(collcollate, "POSIX") == 0));
-		cache_entry->ctype_is_c = ((strcmp(collctype, "C") == 0) ||
-								   (strcmp(collctype, "POSIX") == 0));
+		if (collform->collprovider == COLLPROVIDER_LIBC)
+		{
+			Datum		datum;
+			bool		isnull;
+			const char *collcollate;
+			const char *collctype;
+
+			datum = SysCacheGetAttr(COLLOID, tp, Anum_pg_collation_collcollate, &isnull);
+			Assert(!isnull);
+			collcollate = TextDatumGetCString(datum);
+			datum = SysCacheGetAttr(COLLOID, tp, Anum_pg_collation_collctype, &isnull);
+			Assert(!isnull);
+			collctype = TextDatumGetCString(datum);
+
+			cache_entry->collate_is_c = ((strcmp(collcollate, "C") == 0) ||
+										 (strcmp(collcollate, "POSIX") == 0));
+			cache_entry->ctype_is_c = ((strcmp(collctype, "C") == 0) ||
+									   (strcmp(collctype, "POSIX") == 0));
+		}
+		else
+		{
+			cache_entry->collate_is_c = false;
+			cache_entry->ctype_is_c = false;
+		}
 
 		cache_entry->flags_valid = true;
 
@@ -1340,6 +1351,9 @@ lc_collate_is_c(Oid collation)
 		static int	result = -1;
 		char	   *localeptr;
 
+		if (default_locale.provider == COLLPROVIDER_ICU)
+			return false;
+
 		if (result >= 0)
 			return (bool) result;
 		localeptr = setlocale(LC_COLLATE, NULL);
@@ -1390,6 +1404,9 @@ lc_ctype_is_c(Oid collation)
 		static int	result = -1;
 		char	   *localeptr;
 
+		if (default_locale.provider == COLLPROVIDER_ICU)
+			return false;
+
 		if (result >= 0)
 			return (bool) result;
 		localeptr = setlocale(LC_CTYPE, NULL);
@@ -1418,6 +1435,38 @@ lc_ctype_is_c(Oid collation)
 	return (lookup_collation_cache(collation, true))->ctype_is_c;
 }
 
+struct pg_locale_struct default_locale;
+
+void
+make_icu_collator(const char *iculocstr,
+				  struct pg_locale_struct *resultp)
+{
+#ifdef USE_ICU
+	UCollator  *collator;
+	UErrorCode	status;
+
+	status = U_ZERO_ERROR;
+	collator = ucol_open(iculocstr, &status);
+	if (U_FAILURE(status))
+		ereport(ERROR,
+				(errmsg("could not open collator for locale \"%s\": %s",
+						iculocstr, u_errorName(status))));
+
+	if (U_ICU_VERSION_MAJOR_NUM < 54)
+		icu_set_collation_attributes(collator, iculocstr);
+
+	/* We will leak this string if the caller errors later :-( */
+	resultp->info.icu.locale = MemoryContextStrdup(TopMemoryContext, iculocstr);
+	resultp->info.icu.ucol = collator;
+#else							/* not USE_ICU */
+	/* could get here if a collation was created by a build with ICU */
+	ereport(ERROR,
+			(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+			 errmsg("ICU is not supported in this build"), \
+			 errhint("You need to rebuild PostgreSQL using %s.", "--with-icu")));
+#endif							/* not USE_ICU */
+}
+
 
 /* simple subroutine for reporting errors from newlocale() */
 #ifdef HAVE_LOCALE_T
@@ -1475,7 +1524,12 @@ pg_newlocale_from_collation(Oid collid)
 	Assert(OidIsValid(collid));
 
 	if (collid == DEFAULT_COLLATION_OID)
-		return (pg_locale_t) 0;
+	{
+		if (default_locale.provider == COLLPROVIDER_ICU)
+			return &default_locale;
+		else
+			return (pg_locale_t) 0;
+	}
 
 	cache_entry = lookup_collation_cache(collid, false);
 
@@ -1484,8 +1538,6 @@ pg_newlocale_from_collation(Oid collid)
 		/* We haven't computed this yet in this session, so do it */
 		HeapTuple	tp;
 		Form_pg_collation collform;
-		const char *collcollate;
-		const char *collctype pg_attribute_unused();
 		struct pg_locale_struct result;
 		pg_locale_t resultp;
 		Datum		datum;
@@ -1496,13 +1548,6 @@ pg_newlocale_from_collation(Oid collid)
 			elog(ERROR, "cache lookup failed for collation %u", collid);
 		collform = (Form_pg_collation) GETSTRUCT(tp);
 
-		datum = SysCacheGetAttr(COLLOID, tp, Anum_pg_collation_collcollate, &isnull);
-		Assert(!isnull);
-		collcollate = TextDatumGetCString(datum);
-		datum = SysCacheGetAttr(COLLOID, tp, Anum_pg_collation_collctype, &isnull);
-		Assert(!isnull);
-		collctype = TextDatumGetCString(datum);
-
 		/* We'll fill in the result struct locally before allocating memory */
 		memset(&result, 0, sizeof(result));
 		result.provider = collform->collprovider;
@@ -1511,8 +1556,17 @@ pg_newlocale_from_collation(Oid collid)
 		if (collform->collprovider == COLLPROVIDER_LIBC)
 		{
 #ifdef HAVE_LOCALE_T
+			const char *collcollate;
+			const char *collctype pg_attribute_unused();
 			locale_t	loc;
 
+			datum = SysCacheGetAttr(COLLOID, tp, Anum_pg_collation_collcollate, &isnull);
+			Assert(!isnull);
+			collcollate = TextDatumGetCString(datum);
+			datum = SysCacheGetAttr(COLLOID, tp, Anum_pg_collation_collctype, &isnull);
+			Assert(!isnull);
+			collctype = TextDatumGetCString(datum);
+
 			if (strcmp(collcollate, collctype) == 0)
 			{
 				/* Normal case where they're the same */
@@ -1563,36 +1617,12 @@ pg_newlocale_from_collation(Oid collid)
 		}
 		else if (collform->collprovider == COLLPROVIDER_ICU)
 		{
-#ifdef USE_ICU
-			UCollator  *collator;
-			UErrorCode	status;
-
-			if (strcmp(collcollate, collctype) != 0)
-				ereport(ERROR,
-						(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-						 errmsg("collations with different collate and ctype values are not supported by ICU")));
-
-			status = U_ZERO_ERROR;
-			collator = ucol_open(collcollate, &status);
-			if (U_FAILURE(status))
-				ereport(ERROR,
-						(errmsg("could not open collator for locale \"%s\": %s",
-								collcollate, u_errorName(status))));
+			const char *iculocstr;
 
-			if (U_ICU_VERSION_MAJOR_NUM < 54)
-				icu_set_collation_attributes(collator, collcollate);
-
-			/* We will leak this string if we get an error below :-( */
-			result.info.icu.locale = MemoryContextStrdup(TopMemoryContext,
-														 collcollate);
-			result.info.icu.ucol = collator;
-#else							/* not USE_ICU */
-			/* could get here if a collation was created by a build with ICU */
-			ereport(ERROR,
-					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-					 errmsg("ICU is not supported in this build"), \
-					 errhint("You need to rebuild PostgreSQL using %s.", "--with-icu")));
-#endif							/* not USE_ICU */
+			datum = SysCacheGetAttr(COLLOID, tp, Anum_pg_collation_colliculocale, &isnull);
+			Assert(!isnull);
+			iculocstr = TextDatumGetCString(datum);
+			make_icu_collator(iculocstr, &result);
 		}
 
 		datum = SysCacheGetAttr(COLLOID, tp, Anum_pg_collation_collversion,
@@ -1604,7 +1634,11 @@ pg_newlocale_from_collation(Oid collid)
 
 			collversionstr = TextDatumGetCString(datum);
 
-			actual_versionstr = get_collation_actual_version(collform->collprovider, collcollate);
+			datum = SysCacheGetAttr(COLLOID, tp, collform->collprovider == COLLPROVIDER_ICU ? Anum_pg_collation_colliculocale : Anum_pg_collation_collcollate, &isnull);
+			Assert(!isnull);
+
+			actual_versionstr = get_collation_actual_version(collform->collprovider,
+															 TextDatumGetCString(datum));
 			if (!actual_versionstr)
 			{
 				/*
diff --git a/src/backend/utils/init/postinit.c b/src/backend/utils/init/postinit.c
index 86d193c89f..6452b42dbf 100644
--- a/src/backend/utils/init/postinit.c
+++ b/src/backend/utils/init/postinit.c
@@ -318,6 +318,7 @@ CheckMyDatabase(const char *name, bool am_superuser, bool override_allow_connect
 	bool		isnull;
 	char	   *collate;
 	char	   *ctype;
+	char	   *iculocale;
 
 	/* Fetch our pg_database row normally, via syscache */
 	tup = SearchSysCache1(DATABASEOID, ObjectIdGetDatum(MyDatabaseId));
@@ -420,6 +421,24 @@ CheckMyDatabase(const char *name, bool am_superuser, bool override_allow_connect
 						   " which is not recognized by setlocale().", ctype),
 				 errhint("Recreate the database with another locale or install the missing locale.")));
 
+	if (dbform->datlocprovider == COLLPROVIDER_ICU)
+	{
+		datum = SysCacheGetAttr(DATABASEOID, tup, Anum_pg_database_daticulocale, &isnull);
+		Assert(!isnull);
+		iculocale = TextDatumGetCString(datum);
+		make_icu_collator(iculocale, &default_locale);
+	}
+	else
+		iculocale = NULL;
+
+	default_locale.provider = dbform->datlocprovider;
+	/*
+	 * Default locale is currently always deterministic.  Nondeterministic
+	 * locales currently don't support pattern matching, which would break a
+	 * lot of things if applied globally.
+	 */
+	default_locale.deterministic = true;
+
 	/*
 	 * Check collation version.  See similar code in
 	 * pg_newlocale_from_collation().  Note that here we warn instead of error
@@ -434,7 +453,7 @@ CheckMyDatabase(const char *name, bool am_superuser, bool override_allow_connect
 
 		collversionstr = TextDatumGetCString(datum);
 
-		actual_versionstr = get_collation_actual_version(COLLPROVIDER_LIBC, collate);
+		actual_versionstr = get_collation_actual_version(dbform->datlocprovider, dbform->datlocprovider == COLLPROVIDER_ICU ? iculocale : collate);
 		if (!actual_versionstr)
 			ereport(WARNING,
 					(errmsg("database \"%s\" has no actual collation version, but a version was recorded",
diff --git a/src/bin/initdb/Makefile b/src/bin/initdb/Makefile
index eba282267a..8dd25e7afc 100644
--- a/src/bin/initdb/Makefile
+++ b/src/bin/initdb/Makefile
@@ -40,7 +40,7 @@ OBJS = \
 all: initdb
 
 initdb: $(OBJS) | submake-libpq submake-libpgport submake-libpgfeutils
-	$(CC) $(CFLAGS) $(OBJS) $(LDFLAGS) $(LDFLAGS_EX) $(LIBS) -o $@$(X)
+	$(CC) $(CFLAGS) $(OBJS) $(LDFLAGS) $(LDFLAGS_EX) $(LIBS) $(ICU_LIBS) -o $@$(X)
 
 # We must pull in localtime.c from src/timezones
 localtime.c: % : $(top_srcdir)/src/timezone/%
@@ -62,6 +62,8 @@ clean distclean maintainer-clean:
 # ensure that changes in datadir propagate into object file
 initdb.o: initdb.c $(top_builddir)/src/Makefile.global
 
+export with_icu
+
 check:
 	$(prove_check)
 
diff --git a/src/bin/initdb/initdb.c b/src/bin/initdb/initdb.c
index 97f15971e2..cbcd55288f 100644
--- a/src/bin/initdb/initdb.c
+++ b/src/bin/initdb/initdb.c
@@ -55,6 +55,10 @@
 #include <signal.h>
 #include <time.h>
 
+#ifdef USE_ICU
+#include <unicode/ucol.h>
+#endif
+
 #ifdef HAVE_SHM_OPEN
 #include "sys/mman.h"
 #endif
@@ -132,6 +136,8 @@ static char *lc_monetary = NULL;
 static char *lc_numeric = NULL;
 static char *lc_time = NULL;
 static char *lc_messages = NULL;
+static char locale_provider = COLLPROVIDER_LIBC;
+static char *icu_locale = NULL;
 static const char *default_text_search_config = NULL;
 static char *username = NULL;
 static bool pwprompt = false;
@@ -1405,6 +1411,12 @@ bootstrap_template1(void)
 	bki_lines = replace_token(bki_lines, "LC_CTYPE",
 							  escape_quotes_bki(lc_ctype));
 
+	bki_lines = replace_token(bki_lines, "ICU_LOCALE",
+							  locale_provider == COLLPROVIDER_ICU ? escape_quotes_bki(icu_locale) : "_null_");
+
+	sprintf(buf, "%c", locale_provider);
+	bki_lines = replace_token(bki_lines, "LOCALE_PROVIDER", buf);
+
 	/* Also ensure backend isn't confused by this environment var: */
 	unsetenv("PGCLIENTENCODING");
 
@@ -2165,7 +2177,6 @@ setlocales(void)
 	 * canonicalize locale names, and obtain any missing values from our
 	 * current environment
 	 */
-
 	check_locale_name(LC_CTYPE, lc_ctype, &canonname);
 	lc_ctype = canonname;
 	check_locale_name(LC_COLLATE, lc_collate, &canonname);
@@ -2184,6 +2195,37 @@ setlocales(void)
 	check_locale_name(LC_CTYPE, lc_messages, &canonname);
 	lc_messages = canonname;
 #endif
+
+	if (locale_provider == COLLPROVIDER_ICU)
+	{
+		if (!icu_locale)
+		{
+			pg_log_error("ICU locale must be specified");
+			exit(1);
+		}
+
+		/*
+		 * Check ICU locale ID
+		 */
+#ifdef USE_ICU
+		{
+			UErrorCode	status;
+
+			status = U_ZERO_ERROR;
+			ucol_open(icu_locale, &status);
+			if (U_FAILURE(status))
+			{
+				pg_log_error("could not open collator for locale \"%s\": %s",
+							 icu_locale, u_errorName(status));
+				exit(1);
+			}
+		}
+#else
+		pg_log_error("ICU is not supported in this build");
+		fprintf(stderr, _("You need to rebuild PostgreSQL using %s.\n"), "--with-icu");
+		exit(1);
+#endif
+	}
 }
 
 /*
@@ -2202,6 +2244,7 @@ usage(const char *progname)
 	printf(_(" [-D, --pgdata=]DATADIR     location for this database cluster\n"));
 	printf(_("  -E, --encoding=ENCODING   set default encoding for new databases\n"));
 	printf(_("  -g, --allow-group-access  allow group read/execute on data directory\n"));
+	printf(_("      --icu-locale=LOCALE   set ICU locale ID for new databases\n"));
 	printf(_("  -k, --data-checksums      use data page checksums\n"));
 	printf(_("      --locale=LOCALE       set default locale for new databases\n"));
 	printf(_("      --lc-collate=, --lc-ctype=, --lc-messages=LOCALE\n"
@@ -2209,6 +2252,8 @@ usage(const char *progname)
 			 "                            set default locale in the respective category for\n"
 			 "                            new databases (default taken from environment)\n"));
 	printf(_("      --no-locale           equivalent to --locale=C\n"));
+	printf(_("      --locale-provider={libc|icu}\n"
+			 "                            set default locale provider for new databases\n"));
 	printf(_("      --pwfile=FILE         read password for the new superuser from file\n"));
 	printf(_("  -T, --text-search-config=CFG\n"
 			 "                            default text search configuration\n"));
@@ -2372,21 +2417,26 @@ setup_locale_encoding(void)
 {
 	setlocales();
 
-	if (strcmp(lc_ctype, lc_collate) == 0 &&
+	if (locale_provider == COLLPROVIDER_LIBC &&
+		strcmp(lc_ctype, lc_collate) == 0 &&
 		strcmp(lc_ctype, lc_time) == 0 &&
 		strcmp(lc_ctype, lc_numeric) == 0 &&
 		strcmp(lc_ctype, lc_monetary) == 0 &&
-		strcmp(lc_ctype, lc_messages) == 0)
+		strcmp(lc_ctype, lc_messages) == 0 &&
+		(!icu_locale || strcmp(lc_ctype, icu_locale) == 0))
 		printf(_("The database cluster will be initialized with locale \"%s\".\n"), lc_ctype);
 	else
 	{
-		printf(_("The database cluster will be initialized with locales\n"
-				 "  COLLATE:  %s\n"
-				 "  CTYPE:    %s\n"
-				 "  MESSAGES: %s\n"
-				 "  MONETARY: %s\n"
-				 "  NUMERIC:  %s\n"
-				 "  TIME:     %s\n"),
+		printf(_("The database cluster will be initialized with this locale configuration:\n"));
+		printf(_("  provider:    %s\n"), collprovider_name(locale_provider));
+		if (icu_locale)
+			printf(_("  ICU locale:  %s\n"), icu_locale);
+		printf(_("  LC_COLLATE:  %s\n"
+				 "  LC_CTYPE:    %s\n"
+				 "  LC_MESSAGES: %s\n"
+				 "  LC_MONETARY: %s\n"
+				 "  LC_NUMERIC:  %s\n"
+				 "  LC_TIME:     %s\n"),
 			   lc_collate,
 			   lc_ctype,
 			   lc_messages,
@@ -2395,7 +2445,9 @@ setup_locale_encoding(void)
 			   lc_time);
 	}
 
-	if (!encoding)
+	if (!encoding && locale_provider == COLLPROVIDER_ICU)
+		encodingid = PG_UTF8;
+	else if (!encoding)
 	{
 		int			ctype_enc;
 
@@ -2899,6 +2951,8 @@ main(int argc, char *argv[])
 		{"data-checksums", no_argument, NULL, 'k'},
 		{"allow-group-access", no_argument, NULL, 'g'},
 		{"discard-caches", no_argument, NULL, 14},
+		{"locale-provider", required_argument, NULL, 15},
+		{"icu-locale", required_argument, NULL, 16},
 		{NULL, 0, NULL, 0}
 	};
 
@@ -3045,6 +3099,20 @@ main(int argc, char *argv[])
 										 extra_options,
 										 "-c debug_discard_caches=1");
 				break;
+			case 15:
+				if (strcmp(optarg, "icu") == 0)
+					locale_provider = COLLPROVIDER_ICU;
+				else if (strcmp(optarg, "libc") == 0)
+					locale_provider = COLLPROVIDER_LIBC;
+				else
+				{
+					pg_log_error("unrecognized locale provider: %s", optarg);
+					exit(1);
+				}
+				break;
+			case 16:
+				icu_locale = pg_strdup(optarg);
+				break;
 			default:
 				/* getopt_long already emitted a complaint */
 				fprintf(stderr, _("Try \"%s --help\" for more information.\n"),
@@ -3073,6 +3141,13 @@ main(int argc, char *argv[])
 		exit(1);
 	}
 
+	if (icu_locale && locale_provider != COLLPROVIDER_ICU)
+	{
+		pg_log_error("%s cannot be specified unless locale provider \"%s\" is chosen",
+					 "--icu-locale", "icu");
+		exit(1);
+	}
+
 	atexit(cleanup_directories_atexit);
 
 	/* If we only need to fsync, just do it and exit */
diff --git a/src/bin/initdb/t/001_initdb.pl b/src/bin/initdb/t/001_initdb.pl
index 7dc8cdd855..c636bf3ab2 100644
--- a/src/bin/initdb/t/001_initdb.pl
+++ b/src/bin/initdb/t/001_initdb.pl
@@ -93,4 +93,31 @@
 		'check PGDATA permissions');
 }
 
+# Locale provider tests
+
+if ($ENV{with_icu} eq 'yes')
+{
+	command_fails_like(['initdb', '--no-sync', '--locale-provider=icu', "$tempdir/data2"],
+		qr/initdb: error: ICU locale must be specified/,
+		'locale provider ICU requires --icu-locale');
+
+	command_ok(['initdb', '--no-sync', '--locale-provider=icu', '--icu-locale=en', "$tempdir/data3"],
+		'option --icu-locale');
+
+	command_fails_like(['initdb', '--no-sync', '--locale-provider=icu', '--icu-locale=@colNumeric=lower', "$tempdir/dataX"],
+		qr/initdb: error: could not open collator for locale/,
+		'fails for invalid ICU locale');
+}
+else
+{
+	command_fails(['initdb', '--no-sync', '--locale-provider=icu', "$tempdir/data2"],
+				  'locale provider ICU fails since no ICU support');
+}
+
+command_fails(['initdb', '--no-sync', '--locale-provider=xyz', "$tempdir/dataX"],
+			  'fails for invalid locale provider');
+
+command_fails(['initdb', '--no-sync', '--locale-provider=libc', '--icu-locale=en', "$tempdir/dataX"],
+			  'fails for invalid option combination');
+
 done_testing();
diff --git a/src/bin/pg_dump/pg_dump.c b/src/bin/pg_dump/pg_dump.c
index 4dd24b8c89..725cd2e4eb 100644
--- a/src/bin/pg_dump/pg_dump.c
+++ b/src/bin/pg_dump/pg_dump.c
@@ -2753,8 +2753,10 @@ dumpDatabase(Archive *fout)
 				i_datname,
 				i_datdba,
 				i_encoding,
+				i_datlocprovider,
 				i_collate,
 				i_ctype,
+				i_daticulocale,
 				i_frozenxid,
 				i_minmxid,
 				i_datacl,
@@ -2769,8 +2771,10 @@ dumpDatabase(Archive *fout)
 	const char *datname,
 			   *dba,
 			   *encoding,
+			   *datlocprovider,
 			   *collate,
 			   *ctype,
+			   *iculocale,
 			   *datistemplate,
 			   *datconnlimit,
 			   *tablespace;
@@ -2794,9 +2798,9 @@ dumpDatabase(Archive *fout)
 	else
 		appendPQExpBuffer(dbQry, "0 AS datminmxid, ");
 	if (fout->remoteVersion >= 150000)
-		appendPQExpBuffer(dbQry, "datcollversion, ");
+		appendPQExpBuffer(dbQry, "datlocprovider, daticulocale, datcollversion, ");
 	else
-		appendPQExpBuffer(dbQry, "NULL AS datcollversion, ");
+		appendPQExpBuffer(dbQry, "'c' AS datlocprovider, NULL AS daticulocale, NULL AS datcollversion, ");
 	appendPQExpBuffer(dbQry,
 					  "(SELECT spcname FROM pg_tablespace t WHERE t.oid = dattablespace) AS tablespace, "
 					  "shobj_description(oid, 'pg_database') AS description "
@@ -2810,8 +2814,10 @@ dumpDatabase(Archive *fout)
 	i_datname = PQfnumber(res, "datname");
 	i_datdba = PQfnumber(res, "datdba");
 	i_encoding = PQfnumber(res, "encoding");
+	i_datlocprovider = PQfnumber(res, "datlocprovider");
 	i_collate = PQfnumber(res, "datcollate");
 	i_ctype = PQfnumber(res, "datctype");
+	i_daticulocale = PQfnumber(res, "daticulocale");
 	i_frozenxid = PQfnumber(res, "datfrozenxid");
 	i_minmxid = PQfnumber(res, "datminmxid");
 	i_datacl = PQfnumber(res, "datacl");
@@ -2826,8 +2832,13 @@ dumpDatabase(Archive *fout)
 	datname = PQgetvalue(res, 0, i_datname);
 	dba = getRoleName(PQgetvalue(res, 0, i_datdba));
 	encoding = PQgetvalue(res, 0, i_encoding);
+	datlocprovider = PQgetvalue(res, 0, i_datlocprovider);
 	collate = PQgetvalue(res, 0, i_collate);
 	ctype = PQgetvalue(res, 0, i_ctype);
+	if (!PQgetisnull(res, 0, i_daticulocale))
+		iculocale = PQgetvalue(res, 0, i_daticulocale);
+	else
+		iculocale = NULL;
 	frozenxid = atooid(PQgetvalue(res, 0, i_frozenxid));
 	minmxid = atooid(PQgetvalue(res, 0, i_minmxid));
 	dbdacl.acl = PQgetvalue(res, 0, i_datacl);
@@ -2859,6 +2870,16 @@ dumpDatabase(Archive *fout)
 		appendPQExpBufferStr(creaQry, " ENCODING = ");
 		appendStringLiteralAH(creaQry, encoding, fout);
 	}
+
+	appendPQExpBufferStr(creaQry, " LOCALE_PROVIDER = ");
+	if (datlocprovider[0] == 'c')
+		appendPQExpBufferStr(creaQry, "libc");
+	else if (datlocprovider[0] == 'i')
+		appendPQExpBufferStr(creaQry, "icu");
+	else
+		fatal("unrecognized locale provider: %s",
+			  datlocprovider);
+
 	if (strlen(collate) > 0 && strcmp(collate, ctype) == 0)
 	{
 		appendPQExpBufferStr(creaQry, " LOCALE = ");
@@ -2877,6 +2898,11 @@ dumpDatabase(Archive *fout)
 			appendStringLiteralAH(creaQry, ctype, fout);
 		}
 	}
+	if (iculocale)
+	{
+		appendPQExpBufferStr(creaQry, " ICU_LOCALE = ");
+		appendStringLiteralAH(creaQry, iculocale, fout);
+	}
 
 	/*
 	 * For binary upgrade, carry over the collation version.  For normal
diff --git a/src/bin/pg_upgrade/check.c b/src/bin/pg_upgrade/check.c
index 019bcb6c7b..cf3b398d9e 100644
--- a/src/bin/pg_upgrade/check.c
+++ b/src/bin/pg_upgrade/check.c
@@ -10,6 +10,7 @@
 #include "postgres_fe.h"
 
 #include "catalog/pg_authid_d.h"
+#include "catalog/pg_collation.h"
 #include "fe_utils/string_utils.h"
 #include "mb/pg_wchar.h"
 #include "pg_upgrade.h"
@@ -349,6 +350,18 @@ check_locale_and_encoding(DbInfo *olddb, DbInfo *newdb)
 	if (!equivalent_locale(LC_CTYPE, olddb->db_ctype, newdb->db_ctype))
 		pg_fatal("lc_ctype values for database \"%s\" do not match:  old \"%s\", new \"%s\"\n",
 				 olddb->db_name, olddb->db_ctype, newdb->db_ctype);
+	if (olddb->db_collprovider != newdb->db_collprovider)
+		pg_fatal("locale providers for database \"%s\" do not match:  old \"%s\", new \"%s\"\n",
+				 olddb->db_name,
+				 collprovider_name(olddb->db_collprovider),
+				 collprovider_name(newdb->db_collprovider));
+	if ((olddb->db_iculocale == NULL && newdb->db_iculocale != NULL) ||
+		(olddb->db_iculocale != NULL && newdb->db_iculocale == NULL) ||
+		(olddb->db_iculocale != NULL && newdb->db_iculocale != NULL && strcmp(olddb->db_iculocale, newdb->db_iculocale) != 0))
+		pg_fatal("ICU locale values for database \"%s\" do not match:  old \"%s\", new \"%s\"\n",
+				 olddb->db_name,
+				 olddb->db_iculocale ? olddb->db_iculocale : "(null)",
+				 newdb->db_iculocale ? newdb->db_iculocale : "(null)");
 }
 
 /*
diff --git a/src/bin/pg_upgrade/info.c b/src/bin/pg_upgrade/info.c
index 69ef23119f..5c3968e0ea 100644
--- a/src/bin/pg_upgrade/info.c
+++ b/src/bin/pg_upgrade/info.c
@@ -312,11 +312,20 @@ get_db_infos(ClusterInfo *cluster)
 				i_encoding,
 				i_datcollate,
 				i_datctype,
+				i_datlocprovider,
+				i_daticulocale,
 				i_spclocation;
 	char		query[QUERY_ALLOC];
 
 	snprintf(query, sizeof(query),
-			 "SELECT d.oid, d.datname, d.encoding, d.datcollate, d.datctype, "
+			 "SELECT d.oid, d.datname, d.encoding, d.datcollate, d.datctype, ");
+	if (GET_MAJOR_VERSION(old_cluster.major_version) <= 1500)
+		snprintf(query + strlen(query), sizeof(query) - strlen(query),
+				 "'c' AS datlocprovider, NULL AS daticulocale, ");
+	else
+		snprintf(query + strlen(query), sizeof(query) - strlen(query),
+				 "datlocprovider, daticulocale, ");
+	snprintf(query + strlen(query), sizeof(query) - strlen(query),
 			 "pg_catalog.pg_tablespace_location(t.oid) AS spclocation "
 			 "FROM pg_catalog.pg_database d "
 			 " LEFT OUTER JOIN pg_catalog.pg_tablespace t "
@@ -331,6 +340,8 @@ get_db_infos(ClusterInfo *cluster)
 	i_encoding = PQfnumber(res, "encoding");
 	i_datcollate = PQfnumber(res, "datcollate");
 	i_datctype = PQfnumber(res, "datctype");
+	i_datlocprovider = PQfnumber(res, "datlocprovider");
+	i_daticulocale = PQfnumber(res, "daticulocale");
 	i_spclocation = PQfnumber(res, "spclocation");
 
 	ntups = PQntuples(res);
@@ -343,6 +354,11 @@ get_db_infos(ClusterInfo *cluster)
 		dbinfos[tupnum].db_encoding = atoi(PQgetvalue(res, tupnum, i_encoding));
 		dbinfos[tupnum].db_collate = pg_strdup(PQgetvalue(res, tupnum, i_datcollate));
 		dbinfos[tupnum].db_ctype = pg_strdup(PQgetvalue(res, tupnum, i_datctype));
+		dbinfos[tupnum].db_collprovider = PQgetvalue(res, tupnum, i_datlocprovider)[0];
+		if (PQgetisnull(res, tupnum, i_daticulocale))
+			dbinfos[tupnum].db_iculocale = NULL;
+		else
+			dbinfos[tupnum].db_iculocale = pg_strdup(PQgetvalue(res, tupnum, i_daticulocale));
 		snprintf(dbinfos[tupnum].db_tablespace, sizeof(dbinfos[tupnum].db_tablespace), "%s",
 				 PQgetvalue(res, tupnum, i_spclocation));
 	}
diff --git a/src/bin/pg_upgrade/pg_upgrade.h b/src/bin/pg_upgrade/pg_upgrade.h
index b9b3ac81b2..6d7fd88c0c 100644
--- a/src/bin/pg_upgrade/pg_upgrade.h
+++ b/src/bin/pg_upgrade/pg_upgrade.h
@@ -171,6 +171,8 @@ typedef struct
 											 * path */
 	char	   *db_collate;
 	char	   *db_ctype;
+	char		db_collprovider;
+	char	   *db_iculocale;
 	int			db_encoding;
 	RelInfoArr	rel_arr;		/* array of all user relinfos */
 } DbInfo;
diff --git a/src/bin/psql/describe.c b/src/bin/psql/describe.c
index 9229eacb6d..991bfc1546 100644
--- a/src/bin/psql/describe.c
+++ b/src/bin/psql/describe.c
@@ -896,6 +896,18 @@ listAllDbs(const char *pattern, bool verbose)
 					  gettext_noop("Encoding"),
 					  gettext_noop("Collate"),
 					  gettext_noop("Ctype"));
+	if (pset.sversion >= 150000)
+		appendPQExpBuffer(&buf,
+						  "       d.daticulocale as \"%s\",\n"
+						  "       CASE d.datlocprovider WHEN 'c' THEN 'libc' WHEN 'i' THEN 'icu' END AS \"%s\",\n",
+						  gettext_noop("ICU Locale"),
+						  gettext_noop("Locale Provider"));
+	else
+		appendPQExpBuffer(&buf,
+						  "       d.datcollate as \"%s\",\n"
+						  "       'libc' AS \"%s\",\n",
+						  gettext_noop("ICU Locale"),
+						  gettext_noop("Locale Provider"));
 	appendPQExpBufferStr(&buf, "       ");
 	printACLColumn(&buf, "d.datacl");
 	if (verbose)
@@ -4625,7 +4637,7 @@ listCollations(const char *pattern, bool verbose, bool showSystem)
 	PQExpBufferData buf;
 	PGresult   *res;
 	printQueryOpt myopt = pset.popt;
-	static const bool translate_columns[] = {false, false, false, false, false, true, false};
+	static const bool translate_columns[] = {false, false, false, false, false, false, true, false};
 
 	initPQExpBuffer(&buf);
 
@@ -4639,6 +4651,15 @@ listCollations(const char *pattern, bool verbose, bool showSystem)
 					  gettext_noop("Collate"),
 					  gettext_noop("Ctype"));
 
+	if (pset.sversion >= 150000)
+		appendPQExpBuffer(&buf,
+						  ",\n       c.colliculocale AS \"%s\"",
+						  gettext_noop("ICU Locale"));
+	else
+		appendPQExpBuffer(&buf,
+						  ",\n       c.collcollate AS \"%s\"",
+						  gettext_noop("ICU Locale"));
+
 	if (pset.sversion >= 100000)
 		appendPQExpBuffer(&buf,
 						  ",\n       CASE c.collprovider WHEN 'd' THEN 'default' WHEN 'c' THEN 'libc' WHEN 'i' THEN 'icu' END AS \"%s\"",
diff --git a/src/bin/psql/tab-complete.c b/src/bin/psql/tab-complete.c
index 17172827a9..380cbc0b1f 100644
--- a/src/bin/psql/tab-complete.c
+++ b/src/bin/psql/tab-complete.c
@@ -2738,7 +2738,8 @@ psql_completion(const char *text, int start, int end)
 		COMPLETE_WITH("OWNER", "TEMPLATE", "ENCODING", "TABLESPACE",
 					  "IS_TEMPLATE",
 					  "ALLOW_CONNECTIONS", "CONNECTION LIMIT",
-					  "LC_COLLATE", "LC_CTYPE", "LOCALE", "OID");
+					  "LC_COLLATE", "LC_CTYPE", "LOCALE", "OID",
+					  "LOCALE_PROVIDER", "ICU_LOCALE");
 
 	else if (Matches("CREATE", "DATABASE", MatchAny, "TEMPLATE"))
 		COMPLETE_WITH_QUERY(Query_for_list_of_template_databases);
diff --git a/src/bin/scripts/Makefile b/src/bin/scripts/Makefile
index b833109da6..25e7da3d3f 100644
--- a/src/bin/scripts/Makefile
+++ b/src/bin/scripts/Makefile
@@ -53,6 +53,8 @@ clean distclean maintainer-clean:
 	rm -f common.o $(WIN32RES)
 	rm -rf tmp_check
 
+export with_icu
+
 check:
 	$(prove_check)
 
diff --git a/src/bin/scripts/createdb.c b/src/bin/scripts/createdb.c
index b0c6805bc9..6f612abf7c 100644
--- a/src/bin/scripts/createdb.c
+++ b/src/bin/scripts/createdb.c
@@ -38,6 +38,8 @@ main(int argc, char *argv[])
 		{"lc-ctype", required_argument, NULL, 2},
 		{"locale", required_argument, NULL, 'l'},
 		{"maintenance-db", required_argument, NULL, 3},
+		{"locale-provider", required_argument, NULL, 4},
+		{"icu-locale", required_argument, NULL, 5},
 		{NULL, 0, NULL, 0}
 	};
 
@@ -61,6 +63,8 @@ main(int argc, char *argv[])
 	char	   *lc_collate = NULL;
 	char	   *lc_ctype = NULL;
 	char	   *locale = NULL;
+	char	   *locale_provider = NULL;
+	char	   *icu_locale = NULL;
 
 	PQExpBufferData sql;
 
@@ -119,6 +123,12 @@ main(int argc, char *argv[])
 			case 3:
 				maintenance_db = pg_strdup(optarg);
 				break;
+			case 4:
+				locale_provider = pg_strdup(optarg);
+				break;
+			case 5:
+				icu_locale = pg_strdup(optarg);
+				break;
 			default:
 				fprintf(stderr, _("Try \"%s --help\" for more information.\n"), progname);
 				exit(1);
@@ -217,6 +227,13 @@ main(int argc, char *argv[])
 		appendPQExpBufferStr(&sql, " LC_CTYPE ");
 		appendStringLiteralConn(&sql, lc_ctype, conn);
 	}
+	if (locale_provider)
+		appendPQExpBuffer(&sql, " LOCALE_PROVIDER %s", locale_provider);
+	if (icu_locale)
+	{
+		appendPQExpBufferStr(&sql, " ICU_LOCALE ");
+		appendStringLiteralConn(&sql, icu_locale, conn);
+	}
 
 	appendPQExpBufferChar(&sql, ';');
 
@@ -273,6 +290,9 @@ help(const char *progname)
 	printf(_("  -l, --locale=LOCALE          locale settings for the database\n"));
 	printf(_("      --lc-collate=LOCALE      LC_COLLATE setting for the database\n"));
 	printf(_("      --lc-ctype=LOCALE        LC_CTYPE setting for the database\n"));
+	printf(_("      --icu-locale=LOCALE      ICU locale setting for the database\n"));
+	printf(_("      --locale-provider={libc|icu}\n"
+			 "                               locale provider for the database's default collation\n"));
 	printf(_("  -O, --owner=OWNER            database user to own the new database\n"));
 	printf(_("  -T, --template=TEMPLATE      template database to copy\n"));
 	printf(_("  -V, --version                output version information, then exit\n"));
diff --git a/src/bin/scripts/t/020_createdb.pl b/src/bin/scripts/t/020_createdb.pl
index 639245466e..35deec9a92 100644
--- a/src/bin/scripts/t/020_createdb.pl
+++ b/src/bin/scripts/t/020_createdb.pl
@@ -25,9 +25,37 @@
 	qr/statement: CREATE DATABASE foobar2 ENCODING 'LATIN1'/,
 	'create database with encoding');
 
+if ($ENV{with_icu} eq 'yes')
+{
+	# This fails because template0 uses libc provider and has no ICU
+	# locale set.  It would succeed if template0 used the icu
+	# provider.  XXX Maybe split into multiple tests?
+	$node->command_fails(
+		[ 'createdb', '-T', 'template0', '--locale-provider=icu', 'foobar4' ],
+		'create database with ICU fails without ICU locale specified');
+
+	$node->issues_sql_like(
+		[ 'createdb', '-T', 'template0', '--locale-provider=icu', '--icu-locale=en', 'foobar5' ],
+		qr/statement: CREATE DATABASE foobar5 .* LOCALE_PROVIDER icu ICU_LOCALE 'en'/,
+		'create database with ICU locale specified');
+
+	$node->command_fails(
+		[ 'createdb', '-T', 'template0', '--locale-provider=icu', '--icu-locale=@colNumeric=lower', 'foobarX' ],
+		'fails for invalid ICU locale');
+}
+else
+{
+	$node->command_fails(
+		[ 'createdb', '-T', 'template0', '--locale-provider=icu', 'foobar4' ],
+		'create database with ICU fails since no ICU support');
+}
+
 $node->command_fails([ 'createdb', 'foobar1' ],
 	'fails if database already exists');
 
+$node->command_fails([ 'createdb', '-T', 'template0', '--locale-provider=xyz', 'foobarX' ],
+	'fails for invalid locale provider');
+
 # Check use of templates with shared dependencies copied from the template.
 my ($ret, $stdout, $stderr) = $node->psql(
 	'foobar2',
diff --git a/src/include/catalog/pg_collation.dat b/src/include/catalog/pg_collation.dat
index 4b56825d82..f7470ead49 100644
--- a/src/include/catalog/pg_collation.dat
+++ b/src/include/catalog/pg_collation.dat
@@ -14,8 +14,7 @@
 
 { oid => '100', oid_symbol => 'DEFAULT_COLLATION_OID',
   descr => 'database\'s default collation',
-  collname => 'default', collprovider => 'd', collencoding => '-1',
-  collcollate => '', collctype => '' },
+  collname => 'default', collprovider => 'd', collencoding => '-1' },
 { oid => '950', oid_symbol => 'C_COLLATION_OID',
   descr => 'standard C collation',
   collname => 'C', collprovider => 'c', collencoding => '-1',
diff --git a/src/include/catalog/pg_collation.h b/src/include/catalog/pg_collation.h
index 8763dd4080..c642c3bb95 100644
--- a/src/include/catalog/pg_collation.h
+++ b/src/include/catalog/pg_collation.h
@@ -40,8 +40,9 @@ CATALOG(pg_collation,3456,CollationRelationId)
 	bool		collisdeterministic BKI_DEFAULT(t);
 	int32		collencoding;	/* encoding for this collation; -1 = "all" */
 #ifdef CATALOG_VARLEN			/* variable-length fields start here */
-	text		collcollate BKI_FORCE_NOT_NULL;		/* LC_COLLATE setting */
-	text		collctype BKI_FORCE_NOT_NULL;		/* LC_CTYPE setting */
+	text		collcollate BKI_DEFAULT(_null_);	/* LC_COLLATE setting */
+	text		collctype BKI_DEFAULT(_null_);		/* LC_CTYPE setting */
+	text		colliculocale BKI_DEFAULT(_null_);	/* ICU locale ID */
 	text		collversion BKI_DEFAULT(_null_);	/* provider-dependent
 													 * version of collation
 													 * data */
@@ -66,6 +67,20 @@ DECLARE_UNIQUE_INDEX_PKEY(pg_collation_oid_index, 3085, CollationOidIndexId, on
 #define COLLPROVIDER_ICU		'i'
 #define COLLPROVIDER_LIBC		'c'
 
+static inline const char *
+collprovider_name(char c)
+{
+	switch (c)
+	{
+		case COLLPROVIDER_ICU:
+			return "icu";
+		case COLLPROVIDER_LIBC:
+			return "libc";
+		default:
+			return "???";
+	}
+}
+
 #endif							/* EXPOSE_TO_CLIENT_CODE */
 
 
@@ -75,6 +90,7 @@ extern Oid	CollationCreate(const char *collname, Oid collnamespace,
 							bool collisdeterministic,
 							int32 collencoding,
 							const char *collcollate, const char *collctype,
+							const char *colliculocale,
 							const char *collversion,
 							bool if_not_exists,
 							bool quiet);
diff --git a/src/include/catalog/pg_database.dat b/src/include/catalog/pg_database.dat
index e7e42d6023..5feedff7bf 100644
--- a/src/include/catalog/pg_database.dat
+++ b/src/include/catalog/pg_database.dat
@@ -14,9 +14,9 @@
 
 { oid => '1', oid_symbol => 'TemplateDbOid',
   descr => 'default template for new databases',
-  datname => 'template1', encoding => 'ENCODING', datistemplate => 't',
+  datname => 'template1', encoding => 'ENCODING', datlocprovider => 'LOCALE_PROVIDER', datistemplate => 't',
   datallowconn => 't', datconnlimit => '-1', datfrozenxid => '0',
   datminmxid => '1', dattablespace => 'pg_default', datcollate => 'LC_COLLATE',
-  datctype => 'LC_CTYPE', datacl => '_null_' },
+  datctype => 'LC_CTYPE', daticulocale => 'ICU_LOCALE', datacl => '_null_' },
 
 ]
diff --git a/src/include/catalog/pg_database.h b/src/include/catalog/pg_database.h
index 76adbd4aad..a9f4a8071f 100644
--- a/src/include/catalog/pg_database.h
+++ b/src/include/catalog/pg_database.h
@@ -40,6 +40,9 @@ CATALOG(pg_database,1262,DatabaseRelationId) BKI_SHARED_RELATION BKI_ROWTYPE_OID
 	/* character encoding */
 	int32		encoding;
 
+	/* locale provider, see pg_collation.collprovider */
+	char		datlocprovider;
+
 	/* allowed as CREATE DATABASE template? */
 	bool		datistemplate;
 
@@ -65,6 +68,9 @@ CATALOG(pg_database,1262,DatabaseRelationId) BKI_SHARED_RELATION BKI_ROWTYPE_OID
 	/* LC_CTYPE setting */
 	text		datctype BKI_FORCE_NOT_NULL;
 
+	/* ICU locale ID */
+	text		daticulocale;
+
 	/* provider-dependent version of collation data */
 	text		datcollversion BKI_DEFAULT(_null_);
 
diff --git a/src/include/utils/pg_locale.h b/src/include/utils/pg_locale.h
index 30e423af0e..9b158f24a0 100644
--- a/src/include/utils/pg_locale.h
+++ b/src/include/utils/pg_locale.h
@@ -103,6 +103,11 @@ struct pg_locale_struct
 
 typedef struct pg_locale_struct *pg_locale_t;
 
+extern struct pg_locale_struct default_locale;
+
+extern void make_icu_collator(const char *iculocstr,
+							  struct pg_locale_struct *resultp);
+
 extern pg_locale_t pg_newlocale_from_collation(Oid collid);
 
 extern char *get_collation_actual_version(char collprovider, const char *collcollate);
diff --git a/src/test/Makefile b/src/test/Makefile
index 46275915ff..69ef074d75 100644
--- a/src/test/Makefile
+++ b/src/test/Makefile
@@ -14,6 +14,10 @@ include $(top_builddir)/src/Makefile.global
 
 SUBDIRS = perl regress isolation modules authentication recovery subscription
 
+ifeq ($(with_icu),yes)
+SUBDIRS += icu
+endif
+
 # Test suites that are not safe by default but can be run if selected
 # by the user via the whitespace-separated list in variable
 # PG_TEST_EXTRA:
@@ -37,7 +41,7 @@ endif
 # clean" etc to recurse into them.  (We must filter out those that we
 # have conditionally included into SUBDIRS above, else there will be
 # make confusion.)
-ALWAYS_SUBDIRS = $(filter-out $(SUBDIRS),examples kerberos ldap ssl)
+ALWAYS_SUBDIRS = $(filter-out $(SUBDIRS),examples kerberos icu ldap ssl)
 
 # We want to recurse to all subdirs for all standard targets, except that
 # installcheck and install should not recurse into the subdirectory "modules".
diff --git a/src/test/icu/.gitignore b/src/test/icu/.gitignore
new file mode 100644
index 0000000000..871e943d50
--- /dev/null
+++ b/src/test/icu/.gitignore
@@ -0,0 +1,2 @@
+# Generated by test suite
+/tmp_check/
diff --git a/src/test/icu/Makefile b/src/test/icu/Makefile
new file mode 100644
index 0000000000..e30f5e9524
--- /dev/null
+++ b/src/test/icu/Makefile
@@ -0,0 +1,25 @@
+#-------------------------------------------------------------------------
+#
+# Makefile for src/test/icu
+#
+# Portions Copyright (c) 1996-2022, PostgreSQL Global Development Group
+# Portions Copyright (c) 1994, Regents of the University of California
+#
+# src/test/icu/Makefile
+#
+#-------------------------------------------------------------------------
+
+subdir = src/test/icu
+top_builddir = ../../..
+include $(top_builddir)/src/Makefile.global
+
+export with_icu
+
+check:
+	$(prove_check)
+
+installcheck:
+	$(prove_installcheck)
+
+clean distclean maintainer-clean:
+	rm -rf tmp_check
diff --git a/src/test/icu/README b/src/test/icu/README
new file mode 100644
index 0000000000..cfc9353dff
--- /dev/null
+++ b/src/test/icu/README
@@ -0,0 +1,27 @@
+src/test/icu/README
+
+Regression tests for ICU functionality
+======================================
+
+This directory contains a test suite for ICU functionality.
+
+Running the tests
+=================
+
+NOTE: You must have given the --enable-tap-tests argument to configure.
+Also, to use "make installcheck", you must have built and installed
+contrib/hstore in addition to the core code.
+
+Run
+    make check
+or
+    make installcheck
+You can use "make installcheck" if you previously did "make install".
+In that case, the code in the installation tree is tested.  With
+"make check", a temporary installation tree is built from the current
+sources and then tested.
+
+Either way, this test initializes, starts, and stops several test Postgres
+clusters.
+
+See src/test/perl/README for more info about running these tests.
diff --git a/src/test/icu/t/010_database.pl b/src/test/icu/t/010_database.pl
new file mode 100644
index 0000000000..4cc8907b42
--- /dev/null
+++ b/src/test/icu/t/010_database.pl
@@ -0,0 +1,58 @@
+# Copyright (c) 2022, PostgreSQL Global Development Group
+
+use strict;
+use warnings;
+use PostgreSQL::Test::Cluster;
+use PostgreSQL::Test::Utils;
+use Test::More;
+
+if ($ENV{with_icu} ne 'yes')
+{
+	plan skip_all => 'ICU not supported by this build';
+}
+
+my $node1 = PostgreSQL::Test::Cluster->new('node1');
+$node1->init;
+$node1->start;
+
+$node1->safe_psql('postgres',
+	q{CREATE DATABASE dbicu LOCALE_PROVIDER icu LOCALE 'C' ICU_LOCALE 'en-u-kf-upper' TEMPLATE template0});
+
+$node1->safe_psql('dbicu',
+q{
+CREATE COLLATION upperfirst (provider = icu, locale = 'en-u-kf-upper');
+CREATE TABLE icu (def text, en text COLLATE "en-x-icu", upfirst text COLLATE upperfirst);
+INSERT INTO icu VALUES ('a', 'a', 'a'), ('b', 'b', 'b'), ('A', 'A', 'A'), ('B', 'B', 'B');
+});
+
+is($node1->safe_psql('dbicu', q{SELECT def FROM icu ORDER BY def}),
+	qq(A
+a
+B
+b),
+	'sort by database default locale');
+
+is($node1->safe_psql('dbicu', q{SELECT def FROM icu ORDER BY def COLLATE "en-x-icu"}),
+	qq(a
+A
+b
+B),
+	'sort by explicit collation standard');
+
+is($node1->safe_psql('dbicu', q{SELECT def FROM icu ORDER BY en COLLATE upperfirst}),
+	qq(A
+a
+B
+b),
+	'sort by explicit collation upper first');
+
+
+# Test error cases in CREATE DATABASE involving locale-related options
+
+my ($ret, $stdout, $stderr) = $node1->psql('postgres',
+	q{CREATE DATABASE dbicu LOCALE_PROVIDER icu TEMPLATE template0});
+isnt($ret, 0, "ICU locale must be specified for ICU provider: exit code not 0");
+like($stderr, qr/ERROR:  ICU locale must be specified/, "ICU locale must be specified for ICU provider: error message");
+
+
+done_testing();
diff --git a/src/test/regress/expected/collate.icu.utf8.out b/src/test/regress/expected/collate.icu.utf8.out
index 9699ca16cf..d4c8c6de38 100644
--- a/src/test/regress/expected/collate.icu.utf8.out
+++ b/src/test/regress/expected/collate.icu.utf8.out
@@ -1029,14 +1029,12 @@ CREATE COLLATION test0 FROM "C"; -- fail, duplicate name
 ERROR:  collation "test0" already exists
 do $$
 BEGIN
-  EXECUTE 'CREATE COLLATION test1 (provider = icu, lc_collate = ' ||
-          quote_literal(current_setting('lc_collate')) ||
-          ', lc_ctype = ' ||
-          quote_literal(current_setting('lc_ctype')) || ');';
+  EXECUTE 'CREATE COLLATION test1 (provider = icu, locale = ' ||
+          quote_literal(current_setting('lc_collate')) || ');';
 END
 $$;
-CREATE COLLATION test3 (provider = icu, lc_collate = 'en_US.utf8'); -- fail, need lc_ctype
-ERROR:  parameter "lc_ctype" must be specified
+CREATE COLLATION test3 (provider = icu, lc_collate = 'en_US.utf8'); -- fail, needs "locale"
+ERROR:  parameter "locale" must be specified
 CREATE COLLATION testx (provider = icu, locale = 'nonsense'); /* never fails with ICU */  DROP COLLATION testx;
 CREATE COLLATION test4 FROM nonsense;
 ERROR:  collation "nonsense" for encoding "UTF8" does not exist
diff --git a/src/test/regress/sql/collate.icu.utf8.sql b/src/test/regress/sql/collate.icu.utf8.sql
index 242a7ce6b7..b0ddc7db44 100644
--- a/src/test/regress/sql/collate.icu.utf8.sql
+++ b/src/test/regress/sql/collate.icu.utf8.sql
@@ -366,13 +366,11 @@ CREATE SCHEMA test_schema;
 CREATE COLLATION test0 FROM "C"; -- fail, duplicate name
 do $$
 BEGIN
-  EXECUTE 'CREATE COLLATION test1 (provider = icu, lc_collate = ' ||
-          quote_literal(current_setting('lc_collate')) ||
-          ', lc_ctype = ' ||
-          quote_literal(current_setting('lc_ctype')) || ');';
+  EXECUTE 'CREATE COLLATION test1 (provider = icu, locale = ' ||
+          quote_literal(current_setting('lc_collate')) || ');';
 END
 $$;
-CREATE COLLATION test3 (provider = icu, lc_collate = 'en_US.utf8'); -- fail, need lc_ctype
+CREATE COLLATION test3 (provider = icu, lc_collate = 'en_US.utf8'); -- fail, needs "locale"
 CREATE COLLATION testx (provider = icu, locale = 'nonsense'); /* never fails with ICU */  DROP COLLATION testx;
 
 CREATE COLLATION test4 FROM nonsense;

base-commit: 705e20f8550c0e8e47c0b6b20b5f5ffd6ffd9e33
-- 
2.35.1

diff --git a/doc/src/sgml/catalogs.sgml b/doc/src/sgml/catalogs.sgml
index bcf2b43..4dc5b34 100644
--- a/doc/src/sgml/catalogs.sgml
+++ b/doc/src/sgml/catalogs.sgml
@@ -3054,6 +3054,15 @@ SCRAM-SHA-256$<replaceable>&lt;iteration count&gt;</replaceable>:<replaceable>&l
 
      <row>
       <entry role="catalog_table_entry"><para role="column_definition">
+       <structfield>daticulocale</structfield> <type>text</type>
+      </para>
+      <para>
+       ICU locale ID for this database
+      </para></entry>
+     </row>
+
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
        <structfield>datcollversion</structfield> <type>text</type>
       </para>
       <para>

diff --git a/src/backend/utils/adt/pg_locale.c b/src/backend/utils/adt/pg_locale.c
index 1a047a97d74e7fe5b2cad22cd54cf30f7129bf84..21cfbfffdd1b58df821adbdd577fb599bc2747cf 100644
--- a/src/backend/utils/adt/pg_locale.c
+++ b/src/backend/utils/adt/pg_locale.c
@@ -1406,6 +1406,14 @@ make_icu_collator(const char *iculocstr,
 #ifdef USE_ICU
 	UCollator  *collator;
 	UErrorCode	status;
+	const char *default_icu_locale;
+	UVersionInfo versioninfo;
+	char		buf[U_MAX_VERSION_STRING_LENGTH];
+	const char *valid_locale;
+
+	default_icu_locale = uloc_getDefault();
+	elog(LOG, "make_icu_collator uloc_getDefault() %s",
+		 default_icu_locale ? default_icu_locale : "(null)");
 
 	status = U_ZERO_ERROR;
 	collator = ucol_open(iculocstr, &status);
@@ -1417,6 +1425,20 @@ make_icu_collator(const char *iculocstr,
 	if (U_ICU_VERSION_MAJOR_NUM < 54)
 		icu_set_collation_attributes(collator, iculocstr);
 
+	status = U_ZERO_ERROR;
+	valid_locale = ucol_getLocaleByType(collator, ULOC_VALID_LOCALE, &status);
+	if (U_FAILURE(status) || valid_locale == NULL)
+		ereport(ERROR,
+				(errmsg("failed to get valid locale for collator with "
+						"requested locale \"%s\": %s",
+						iculocstr, u_errorName(status))));
+
+	ucol_getVersion(collator, versioninfo);
+	u_versionToString(versioninfo, buf);
+
+	elog(LOG, "make_icu_collator icu_locale %s valid_locale %s version %s",
+		 iculocstr ? iculocstr : "(null)", valid_locale, buf);
+
 	/* We will leak this string if the caller errors later :-( */
 	resultp->info.icu.locale = MemoryContextStrdup(TopMemoryContext, iculocstr);
 	resultp->info.icu.ucol = collator;
@@ -1654,6 +1676,12 @@ get_collation_actual_version(char collprovider, const char *collcollate)
 		UErrorCode	status;
 		UVersionInfo versioninfo;
 		char		buf[U_MAX_VERSION_STRING_LENGTH];
+		const char *default_icu_locale;
+		const char *valid_locale;
+
+		default_icu_locale = uloc_getDefault();
+		elog(LOG, "get_collation_actual_version uloc_getDefault() %s",
+			 default_icu_locale ? default_icu_locale : "(null)");
 
 		status = U_ZERO_ERROR;
 		collator = ucol_open(collcollate, &status);
@@ -1661,10 +1689,25 @@ get_collation_actual_version(char collprovider, const char *collcollate)
 			ereport(ERROR,
 					(errmsg("could not open collator for locale \"%s\": %s",
 							collcollate, u_errorName(status))));
-		ucol_getVersion(collator, versioninfo);
-		ucol_close(collator);
 
+		status = U_ZERO_ERROR;
+		valid_locale = ucol_getLocaleByType(collator, ULOC_VALID_LOCALE,
+											&status);
+		if (U_FAILURE(status) || valid_locale == NULL)
+			ereport(ERROR,
+					(errmsg("failed to get valid locale for collator with "
+							"requested locale \"%s\": %s",
+							collcollate, u_errorName(status))));
+
+		ucol_getVersion(collator, versioninfo);
 		u_versionToString(versioninfo, buf);
+
+		elog(LOG,
+			 "get_collation_actual_version icu_locale %s valid_locale %s "
+			 "version %s",
+			 collcollate ? collcollate : "(null)", valid_locale, buf);
+
+		ucol_close(collator);
 		collversion = pstrdup(buf);
 	}
 	else
@@ -1955,6 +1998,14 @@ check_icu_locale(const char *icu_locale)
 #ifdef USE_ICU
 	UCollator  *collator;
 	UErrorCode	status;
+	const char *default_icu_locale;
+	UVersionInfo versioninfo;
+	char		buf[U_MAX_VERSION_STRING_LENGTH];
+	const char *valid_locale;
+
+	default_icu_locale = uloc_getDefault();
+	elog(LOG, "check_icu_locale uloc_getDefault() %s",
+		 default_icu_locale ? default_icu_locale : "(null)");
 
 	status = U_ZERO_ERROR;
 	collator = ucol_open(icu_locale, &status);
@@ -1965,6 +2016,21 @@ check_icu_locale(const char *icu_locale)
 
 	if (U_ICU_VERSION_MAJOR_NUM < 54)
 		icu_set_collation_attributes(collator, icu_locale);
+
+	status = U_ZERO_ERROR;
+	valid_locale = ucol_getLocaleByType(collator, ULOC_VALID_LOCALE, &status);
+	if (U_FAILURE(status) || valid_locale == NULL)
+		ereport(ERROR,
+				(errmsg("failed to get valid locale for collator with "
+						"requested locale \"%s\": %s",
+						icu_locale, u_errorName(status))));
+
+	ucol_getVersion(collator, versioninfo);
+	u_versionToString(versioninfo, buf);
+
+	elog(LOG, "check_icu_locale icu_locale %s valid_locale %s version %s",
+		 icu_locale ? icu_locale : "(null)", valid_locale, buf);
+
 	ucol_close(collator);
 #else
 	ereport(ERROR,

diff --git a/src/bin/pg_dump/Makefile b/src/bin/pg_dump/Makefile
index 2f524b09bf53a55037013d78148f8cbca4fa7eee..9dc5a784dd2d1ce58a6284f19c54730364779c4d 100644
--- a/src/bin/pg_dump/Makefile
+++ b/src/bin/pg_dump/Makefile
@@ -17,6 +17,7 @@ top_builddir = ../../..
 include $(top_builddir)/src/Makefile.global
 
 export GZIP_PROGRAM=$(GZIP)
+export with_icu
 
 override CPPFLAGS := -I$(libpq_srcdir) $(CPPFLAGS)
 LDFLAGS_INTERNAL += -L$(top_builddir)/src/fe_utils -lpgfeutils $(libpq_pgport)
diff --git a/src/bin/pg_dump/pg_dump.c b/src/bin/pg_dump/pg_dump.c
index 2c6891573296b395c5bd6b627d061de657355e9c..e8e8f69e30c8a787e5dff157f5d1619917638d7d 100644
--- a/src/bin/pg_dump/pg_dump.c
+++ b/src/bin/pg_dump/pg_dump.c
@@ -13084,9 +13084,11 @@ dumpCollation(Archive *fout, const CollInfo *collinfo)
 	int			i_collisdeterministic;
 	int			i_collcollate;
 	int			i_collctype;
+	int			i_colliculocale;
 	const char *collprovider;
 	const char *collcollate;
 	const char *collctype;
+	const char *colliculocale;
 
 	/* Do nothing in data-only dump */
 	if (dopt->dataOnly)
@@ -13117,6 +13119,13 @@ dumpCollation(Archive *fout, const CollInfo *collinfo)
 		appendPQExpBufferStr(query,
 							 "true AS collisdeterministic, ");
 
+	if (fout->remoteVersion >= 150000)
+		appendPQExpBufferStr(query,
+							 "colliculocale, ");
+	else
+		appendPQExpBufferStr(query,
+							 "NULL AS colliculocale, ");
+
 	appendPQExpBuffer(query,
 					  "collcollate, "
 					  "collctype "
@@ -13130,10 +13139,24 @@ dumpCollation(Archive *fout, const CollInfo *collinfo)
 	i_collisdeterministic = PQfnumber(res, "collisdeterministic");
 	i_collcollate = PQfnumber(res, "collcollate");
 	i_collctype = PQfnumber(res, "collctype");
+	i_colliculocale = PQfnumber(res, "colliculocale");
 
 	collprovider = PQgetvalue(res, 0, i_collprovider);
-	collcollate = PQgetvalue(res, 0, i_collcollate);
-	collctype = PQgetvalue(res, 0, i_collctype);
+
+	if (!PQgetisnull(res, 0, i_collcollate))
+		collcollate = PQgetvalue(res, 0, i_collcollate);
+	else
+		collcollate = NULL;
+
+	if (!PQgetisnull(res, 0, i_collctype))
+		collctype = PQgetvalue(res, 0, i_collctype);
+	else
+		collctype = NULL;
+
+	if (!PQgetisnull(res, 0, i_colliculocale))
+		colliculocale = PQgetvalue(res, 0, i_colliculocale);
+	else
+		colliculocale = NULL;
 
 	appendPQExpBuffer(delq, "DROP COLLATION %s;\n",
 					  fmtQualifiedDumpable(collinfo));
@@ -13156,17 +13179,28 @@ dumpCollation(Archive *fout, const CollInfo *collinfo)
 	if (strcmp(PQgetvalue(res, 0, i_collisdeterministic), "f") == 0)
 		appendPQExpBufferStr(q, ", deterministic = false");
 
-	if (strcmp(collcollate, collctype) == 0)
+	if (colliculocale != NULL)
 	{
 		appendPQExpBufferStr(q, ", locale = ");
-		appendStringLiteralAH(q, collcollate, fout);
+		appendStringLiteralAH(q, colliculocale, fout);
 	}
 	else
 	{
-		appendPQExpBufferStr(q, ", lc_collate = ");
-		appendStringLiteralAH(q, collcollate, fout);
-		appendPQExpBufferStr(q, ", lc_ctype = ");
-		appendStringLiteralAH(q, collctype, fout);
+		Assert(collcollate != NULL);
+		Assert(collctype != NULL);
+
+		if (strcmp(collcollate, collctype) == 0)
+		{
+			appendPQExpBufferStr(q, ", locale = ");
+			appendStringLiteralAH(q, collcollate, fout);
+		}
+		else
+		{
+			appendPQExpBufferStr(q, ", lc_collate = ");
+			appendStringLiteralAH(q, collcollate, fout);
+			appendPQExpBufferStr(q, ", lc_ctype = ");
+			appendStringLiteralAH(q, collctype, fout);
+		}
 	}
 
 	/*
diff --git a/src/bin/pg_dump/t/002_pg_dump.pl b/src/bin/pg_dump/t/002_pg_dump.pl
index b10e1c4c0d4d27bf1a427c8cfe36f8dea4dad78a..7f4be26bce6fb37b83e4735c541a2215841f5e95 100644
--- a/src/bin/pg_dump/t/002_pg_dump.pl
+++ b/src/bin/pg_dump/t/002_pg_dump.pl
@@ -1593,6 +1593,15 @@ my %tests = (
 		like      => { %full_runs, section_pre_data => 1, },
 	},
 
+	'CREATE COLLATION icu_collation' => {
+		create_order => 76,
+		create_sql   => "CREATE COLLATION icu_collation (PROVIDER = icu, LOCALE = 'C');",
+		regexp =>
+		  qr/CREATE COLLATION public.icu_collation \(provider = icu, locale = 'C'(, version = '[^']*')?\);/m,
+		icu_collation => 1,
+		like      => { %full_runs, section_pre_data => 1, },
+	},
+
 	'CREATE CAST FOR timestamptz' => {
 		create_order => 51,
 		create_sql =>
@@ -3931,6 +3940,11 @@ foreach my $test (
 		$test_db = $tests{$test}->{database};
 	}
 
+	if (defined($tests{$test}->{icu_collation}))
+	{
+		$tests{$test}->{collation} = 1;
+	}
+
 	if ($tests{$test}->{create_sql})
 	{
 
@@ -3940,6 +3954,12 @@ foreach my $test (
 			next;
 		}
 
+		# Skip any icu-related collation commands if build was without icu
+		if ($ENV{with_icu} ne 'yes' && defined($tests{$test}->{icu_collation}))
+		{
+			next;
+		}
+
 		# Skip tests specific to LZ4 if this build does not support
 		# this option.
 		if (!$supports_lz4 && defined($tests{$test}->{lz4}))
@@ -4141,6 +4161,12 @@ foreach my $run (sort keys %pgdump_runs)
 			next;
 		}
 
+		# Skip any icu-related collation commands if build was without icu
+		if ($ENV{with_icu} ne 'yes' && defined($tests{$test}->{icu_collation}))
+		{
+			next;
+		}
+
 		# Skip tests specific to LZ4 if this build does not support
 		# this option.
 		if (!$supports_lz4 && defined($tests{$test}->{lz4}))

diff --git a/src/backend/commands/dbcommands.c b/src/backend/commands/dbcommands.c
index 6ff48bb18f3639ae45d9528b32df51a4aebc60c0..0a22cace11d9df6b5fc085bfd7b86319f4b13165 100644
--- a/src/backend/commands/dbcommands.c
+++ b/src/backend/commands/dbcommands.c
@@ -851,6 +851,12 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 					 parser_errposition(pstate, defel->location)));
 	}
 
+	if (dlocale && (dcollate || dctype))
+		ereport(ERROR,
+				(errcode(ERRCODE_SYNTAX_ERROR),
+				 errmsg("conflicting or redundant options"),
+				 errdetail("LOCALE cannot be specified together with LC_COLLATE or LC_CTYPE.")));
+
 	if (downer && downer->arg)
 		dbowner = defGetString(downer);
 	if (dtemplate && dtemplate->arg)

diff --git a/src/backend/commands/dbcommands.c b/src/backend/commands/dbcommands.c
index 6ff48bb18f3639ae45d9528b32df51a4aebc60c0..07758d15e8613d5a049537ddf2c5992e57ad6424 100644
--- a/src/backend/commands/dbcommands.c
+++ b/src/backend/commands/dbcommands.c
@@ -1042,11 +1042,16 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 			ereport(ERROR,
 					(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
 					 errmsg("ICU locale must be specified")));
-	}
 
-	if (dblocprovider == COLLPROVIDER_ICU)
 		check_icu_locale(dbiculocale);
 
+		if (!(is_encoding_supported_by_icu(encoding)))
+			ereport(ERROR,
+					(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+					 errmsg("encoding \"%s\" is not supported with ICU provider",
+							pg_encoding_to_char(encoding))));
+	}
+
 	/*
 	 * Check that the new encoding and locale settings match the source
 	 * database.  We insist on this because we simply copy the source data ---
diff --git a/src/bin/initdb/initdb.c b/src/bin/initdb/initdb.c
index e00837ecacf4885cf2a176168c283f3e67c6eb53..8a762ced8340c9d8256f7832a4c19a43f1d5538a 100644
--- a/src/bin/initdb/initdb.c
+++ b/src/bin/initdb/initdb.c
@@ -2362,6 +2362,16 @@ setup_locale_encoding(void)
 	if (!check_locale_encoding(lc_ctype, encodingid) ||
 		!check_locale_encoding(lc_collate, encodingid))
 		exit(1);				/* check_locale_encoding printed the error */
+
+	if (locale_provider == COLLPROVIDER_ICU &&
+		!(is_encoding_supported_by_icu(encodingid)))
+	{
+		pg_log_error("encoding \"%s\" is not supported with ICU provider",
+					 pg_encoding_to_char(encodingid));
+		pg_log_error_hint("Rerun %s and choose a matching combination.",
+						  progname);
+		exit(1);
+	}
 }
 
 
diff --git a/src/bin/initdb/t/001_initdb.pl b/src/bin/initdb/t/001_initdb.pl
index a37f6dd9b334b6ee22d9fdd4d51422795cb54a39..e4bb3d0cdd9c23729c5fb97886374f8df558f239 100644
--- a/src/bin/initdb/t/001_initdb.pl
+++ b/src/bin/initdb/t/001_initdb.pl
@@ -118,6 +118,15 @@ if ($ENV{with_icu} eq 'yes')
 		],
 		qr/FATAL:  could not open collator for locale/,
 		'fails for invalid ICU locale');
+
+	command_fails_like(
+		[
+			'initdb',                '--no-sync',
+			'--locale-provider=icu', '--icu-locale=en',
+			'--encoding=SQL_ASCII',  "$tempdir/dataX"
+		],
+		qr/error: encoding "SQL_ASCII" is not supported with ICU provider/,
+		'encoding "SQL_ASCII" is not supported with ICU provider');
 }
 else
 {
diff --git a/src/bin/scripts/t/020_createdb.pl b/src/bin/scripts/t/020_createdb.pl
index e91c1d013d08d8bd1e3a92f2aba958c5c7713ca6..eaab3caa32669ead068719d98bb953c5c6ff5a17 100644
--- a/src/bin/scripts/t/020_createdb.pl
+++ b/src/bin/scripts/t/020_createdb.pl
@@ -50,6 +50,16 @@ if ($ENV{with_icu} eq 'yes')
 		],
 		'fails for invalid ICU locale');
 
+	$node->command_fails_like(
+		[
+			'createdb',        '-T',
+			'template0',       '--locale-provider=icu',
+			'--icu-locale=en', '--encoding=SQL_ASCII',
+			'foobarX'
+		],
+		qr/ERROR:  encoding "SQL_ASCII" is not supported with ICU provider/,
+		'encoding "SQL_ASCII" is not supported with ICU provider');
+
 	# additional node, which uses the icu provider
 	my $node2 = PostgreSQL::Test::Cluster->new('icu');
 	$node2->init(extra => ['--locale-provider=icu', '--icu-locale=en']);

diff --git a/src/backend/commands/dbcommands.c b/src/backend/commands/dbcommands.c
index 6ff48bb18f3639ae45d9528b32df51a4aebc60c0..f248ad42b77c8c0cf2089963d4357b120914ce20 100644
--- a/src/backend/commands/dbcommands.c
+++ b/src/backend/commands/dbcommands.c
@@ -1034,6 +1034,12 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 
 	if (dblocprovider == COLLPROVIDER_ICU)
 	{
+		if (!(is_encoding_supported_by_icu(encoding)))
+			ereport(ERROR,
+					(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+					 errmsg("encoding \"%s\" is not supported with ICU provider",
+							pg_encoding_to_char(encoding))));
+
 		/*
 		 * This would happen if template0 uses the libc provider but the new
 		 * database uses icu.
@@ -1042,10 +1048,9 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 			ereport(ERROR,
 					(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
 					 errmsg("ICU locale must be specified")));
-	}
 
-	if (dblocprovider == COLLPROVIDER_ICU)
 		check_icu_locale(dbiculocale);
+	}
 
 	/*
 	 * Check that the new encoding and locale settings match the source
diff --git a/src/bin/initdb/initdb.c b/src/bin/initdb/initdb.c
index 6aeec8d426c52414b827686781c245291f27ed1f..999e7c2bf8dc707063eddf19a5c27eed03d3ca09 100644
--- a/src/bin/initdb/initdb.c
+++ b/src/bin/initdb/initdb.c
@@ -2092,20 +2092,30 @@ setlocales(void)
 	check_locale_name(LC_CTYPE, lc_messages, &canonname);
 	lc_messages = canonname;
 #endif
+}
 
-	if (locale_provider == COLLPROVIDER_ICU)
+static void
+check_icu_locale_encoding(void)
+{
+	if (!(is_encoding_supported_by_icu(encodingid)))
 	{
-		if (!icu_locale)
-			pg_fatal("ICU locale must be specified");
+		pg_log_error("encoding \"%s\" is not supported with ICU provider",
+					 pg_encoding_to_char(encodingid));
+		pg_log_error_hint("Rerun %s and choose a matching combination.",
+						  progname);
+		exit(1);
+	}
 
-		/*
-		 * In supported builds, the ICU locale ID will be checked by the
-		 * backend during post-bootstrap initialization.
-		 */
+	if (!icu_locale)
+		pg_fatal("ICU locale must be specified");
+
+	/*
+	 * In supported builds, the ICU locale ID will be checked by the backend
+	 * during post-bootstrap initialization.
+	 */
 #ifndef USE_ICU
-		pg_fatal("ICU is not supported in this build");
+	pg_fatal("ICU is not supported in this build");
 #endif
-	}
 }
 
 /*
@@ -2281,34 +2291,6 @@ setup_locale_encoding(void)
 {
 	setlocales();
 
-	if (locale_provider == COLLPROVIDER_LIBC &&
-		strcmp(lc_ctype, lc_collate) == 0 &&
-		strcmp(lc_ctype, lc_time) == 0 &&
-		strcmp(lc_ctype, lc_numeric) == 0 &&
-		strcmp(lc_ctype, lc_monetary) == 0 &&
-		strcmp(lc_ctype, lc_messages) == 0 &&
-		(!icu_locale || strcmp(lc_ctype, icu_locale) == 0))
-		printf(_("The database cluster will be initialized with locale \"%s\".\n"), lc_ctype);
-	else
-	{
-		printf(_("The database cluster will be initialized with this locale configuration:\n"));
-		printf(_("  provider:    %s\n"), collprovider_name(locale_provider));
-		if (icu_locale)
-			printf(_("  ICU locale:  %s\n"), icu_locale);
-		printf(_("  LC_COLLATE:  %s\n"
-				 "  LC_CTYPE:    %s\n"
-				 "  LC_MESSAGES: %s\n"
-				 "  LC_MONETARY: %s\n"
-				 "  LC_NUMERIC:  %s\n"
-				 "  LC_TIME:     %s\n"),
-			   lc_collate,
-			   lc_ctype,
-			   lc_messages,
-			   lc_monetary,
-			   lc_numeric,
-			   lc_time);
-	}
-
 	if (!encoding && locale_provider == COLLPROVIDER_ICU)
 		encodingid = PG_UTF8;
 	else if (!encoding)
@@ -2350,11 +2332,7 @@ setup_locale_encoding(void)
 #endif
 		}
 		else
-		{
 			encodingid = ctype_enc;
-			printf(_("The default database encoding has accordingly been set to \"%s\".\n"),
-				   pg_encoding_to_char(encodingid));
-		}
 	}
 	else
 		encodingid = get_encoding_id(encoding);
@@ -2362,6 +2340,39 @@ setup_locale_encoding(void)
 	if (!check_locale_encoding(lc_ctype, encodingid) ||
 		!check_locale_encoding(lc_collate, encodingid))
 		exit(1);				/* check_locale_encoding printed the error */
+
+	if (locale_provider == COLLPROVIDER_ICU)
+		check_icu_locale_encoding();
+
+	if (locale_provider == COLLPROVIDER_LIBC &&
+		strcmp(lc_ctype, lc_collate) == 0 &&
+		strcmp(lc_ctype, lc_time) == 0 &&
+		strcmp(lc_ctype, lc_numeric) == 0 &&
+		strcmp(lc_ctype, lc_monetary) == 0 &&
+		strcmp(lc_ctype, lc_messages) == 0)
+		printf(_("The database cluster will be initialized with locale \"%s\".\n"), lc_ctype);
+	else
+	{
+		printf(_("The database cluster will be initialized with this locale configuration:\n"));
+		printf(_("  provider:    %s\n"), collprovider_name(locale_provider));
+		if (icu_locale)
+			printf(_("  ICU locale:  %s\n"), icu_locale);
+		printf(_("  LC_COLLATE:  %s\n"
+				 "  LC_CTYPE:    %s\n"
+				 "  LC_MESSAGES: %s\n"
+				 "  LC_MONETARY: %s\n"
+				 "  LC_NUMERIC:  %s\n"
+				 "  LC_TIME:     %s\n"),
+			   lc_collate,
+			   lc_ctype,
+			   lc_messages,
+			   lc_monetary,
+			   lc_numeric,
+			   lc_time);
+	}
+
+	printf(_("The default database encoding will be set to \"%s\".\n"),
+		   pg_encoding_to_char(encodingid));
 }
 
 
diff --git a/src/bin/initdb/t/001_initdb.pl b/src/bin/initdb/t/001_initdb.pl
index a37f6dd9b334b6ee22d9fdd4d51422795cb54a39..40d6d6305a858ec01587d184c69d4f28d0796d74 100644
--- a/src/bin/initdb/t/001_initdb.pl
+++ b/src/bin/initdb/t/001_initdb.pl
@@ -118,6 +118,15 @@ if ($ENV{with_icu} eq 'yes')
 		],
 		qr/FATAL:  could not open collator for locale/,
 		'fails for invalid ICU locale');
+
+	command_fails_like(
+		[
+			'initdb',                '--no-sync',
+			'--locale-provider=icu', '--encoding=SQL_ASCII',
+			"$tempdir/dataX"
+		],
+		qr/error: encoding "SQL_ASCII" is not supported with ICU provider/,
+		'encoding "SQL_ASCII" is not supported with ICU provider');
 }
 else
 {
diff --git a/src/bin/scripts/t/020_createdb.pl b/src/bin/scripts/t/020_createdb.pl
index e91c1d013d08d8bd1e3a92f2aba958c5c7713ca6..56c578d3d81b8e61b687a8b508b3b741d4df270a 100644
--- a/src/bin/scripts/t/020_createdb.pl
+++ b/src/bin/scripts/t/020_createdb.pl
@@ -50,6 +50,15 @@ if ($ENV{with_icu} eq 'yes')
 		],
 		'fails for invalid ICU locale');
 
+	$node->command_fails_like(
+		[
+			'createdb',             '-T',
+			'template0',            '--locale-provider=icu',
+			'--encoding=SQL_ASCII', 'foobarX'
+		],
+		qr/ERROR:  encoding "SQL_ASCII" is not supported with ICU provider/,
+		'encoding "SQL_ASCII" is not supported with ICU provider');
+
 	# additional node, which uses the icu provider
 	my $node2 = PostgreSQL::Test::Cluster->new('icu');
 	$node2->init(extra => ['--locale-provider=icu', '--icu-locale=en']);

From 5bb07e390baf8a471f7d30582469268c8a6d71ca Mon Sep 17 00:00:00 2001
From: Peter Eisentraut <peter@eisentraut.org>
Date: Tue, 20 Sep 2022 05:50:41 -0400
Subject: [PATCH] Improve ICU option handling in CREATE DATABASE

We check that the ICU locale is only specified if the ICU locale
provider is selected.  But we did that too early.  We need to wait
until we load the settings of the template database, since that could
also set what the locale provider is.

Reported-by: Marina Polyakova <m.polyakova@postgrespro.ru>
Discussion: https://www.postgresql.org/message-id/9ba4cd1ea6ed6b7b15c0ff15e6f540cd@postgrespro.ru
---
 src/backend/commands/dbcommands.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/src/backend/commands/dbcommands.c b/src/backend/commands/dbcommands.c
index cba929b7f998..5dfec5c6b056 100644
--- a/src/backend/commands/dbcommands.c
+++ b/src/backend/commands/dbcommands.c
@@ -907,10 +907,6 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 					 errmsg("unrecognized locale provider: %s",
 							locproviderstr)));
 	}
-	if (diculocale && dblocprovider != COLLPROVIDER_ICU)
-		ereport(ERROR,
-				(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
-				 errmsg("ICU locale cannot be specified unless locale provider is ICU")));
 	if (distemplate && distemplate->arg)
 		dbistemplate = defGetBoolean(distemplate);
 	if (dallowconnections && dallowconnections->arg)
@@ -1050,6 +1046,13 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 
 		check_icu_locale(dbiculocale);
 	}
+	else
+	{
+		if (dbiculocale)
+			ereport(ERROR,
+					(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
+					 errmsg("ICU locale cannot be specified unless locale provider is ICU")));
+	}
 
 	/*
 	 * Check that the new encoding and locale settings match the source
-- 
2.37.3

diff --git a/src/backend/commands/dbcommands.c b/src/backend/commands/dbcommands.c
index e0753c1badcc299e2bac45f3bdd2f23f59d70cbc..2589a2523e07c9543c99c7d7b446438d62382b89 100644
--- a/src/backend/commands/dbcommands.c
+++ b/src/backend/commands/dbcommands.c
@@ -1030,6 +1030,11 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 
 	if (dblocprovider == COLLPROVIDER_ICU)
 	{
+#ifndef USE_ICU
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				 errmsg("ICU is not supported in this build")));
+#else
 		if (!(is_encoding_supported_by_icu(encoding)))
 			ereport(ERROR,
 					(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
@@ -1046,6 +1051,7 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 					 errmsg("ICU locale must be specified")));
 
 		check_icu_locale(dbiculocale);
+#endif
 	}
 	else
 	{
diff --git a/src/backend/utils/adt/pg_locale.c b/src/backend/utils/adt/pg_locale.c
index 2b42d9ccd8b751bcb5cda3a1f4c7803a68bc0a4a..743f11e1d1fd62d500fc2846976472d13e08046b 100644
--- a/src/backend/utils/adt/pg_locale.c
+++ b/src/backend/utils/adt/pg_locale.c
@@ -1945,15 +1945,12 @@ icu_set_collation_attributes(UCollator *collator, const char *loc)
 	}
 }
 
-#endif							/* USE_ICU */
-
 /*
  * Check if the given locale ID is valid, and ereport(ERROR) if it isn't.
  */
 void
 check_icu_locale(const char *icu_locale)
 {
-#ifdef USE_ICU
 	UCollator  *collator;
 	UErrorCode	status;
 
@@ -1967,13 +1964,10 @@ check_icu_locale(const char *icu_locale)
 	if (U_ICU_VERSION_MAJOR_NUM < 54)
 		icu_set_collation_attributes(collator, icu_locale);
 	ucol_close(collator);
-#else
-	ereport(ERROR,
-			(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-			 errmsg("ICU is not supported in this build")));
-#endif
 }
 
+#endif							/* USE_ICU */
+
 /*
  * These functions convert from/to libc's wchar_t, *not* pg_wchar_t.
  * Therefore we keep them here rather than with the mbutils code.
diff --git a/src/bin/initdb/initdb.c b/src/bin/initdb/initdb.c
index f61a04305590c7d09ec59fe202d6f22c0a605827..82e6644f89b07004c067785c86cad83e10b1282c 100644
--- a/src/bin/initdb/initdb.c
+++ b/src/bin/initdb/initdb.c
@@ -2047,9 +2047,12 @@ check_locale_encoding(const char *locale, int user_enc)
  *
  * this should match the similar check in the backend createdb() function
  */
-static bool
+static void
 check_icu_locale_encoding(int user_enc)
 {
+#ifndef USE_ICU
+	pg_fatal("ICU is not supported in this build");
+#else
 	if (!(is_encoding_supported_by_icu(user_enc)))
 	{
 		pg_log_error("encoding mismatch");
@@ -2058,9 +2061,17 @@ check_icu_locale_encoding(int user_enc)
 		pg_log_error_hint("Rerun %s and either do not specify an encoding explicitly, "
 						  "or choose a matching combination.",
 						  progname);
-		return false;
+		exit(1);
 	}
-	return true;
+
+	if (!icu_locale)
+		pg_fatal("ICU locale must be specified");
+
+	/*
+	 * In supported builds, the ICU locale ID will be checked by the backend
+	 * during post-bootstrap initialization.
+	 */
+#endif
 }
 
 /*
@@ -2113,20 +2124,6 @@ setlocales(void)
 	check_locale_name(LC_CTYPE, lc_messages, &canonname);
 	lc_messages = canonname;
 #endif
-
-	if (locale_provider == COLLPROVIDER_ICU)
-	{
-		if (!icu_locale)
-			pg_fatal("ICU locale must be specified");
-
-		/*
-		 * In supported builds, the ICU locale ID will be checked by the
-		 * backend during post-bootstrap initialization.
-		 */
-#ifndef USE_ICU
-		pg_fatal("ICU is not supported in this build");
-#endif
-	}
 }
 
 /*
@@ -2388,9 +2385,8 @@ setup_locale_encoding(void)
 		!check_locale_encoding(lc_collate, encodingid))
 		exit(1);				/* check_locale_encoding printed the error */
 
-	if (locale_provider == COLLPROVIDER_ICU &&
-		!check_icu_locale_encoding(encodingid))
-		exit(1);
+	if (locale_provider == COLLPROVIDER_ICU)
+		check_icu_locale_encoding(encodingid);
 }
 
 
diff --git a/src/bin/initdb/t/001_initdb.pl b/src/bin/initdb/t/001_initdb.pl
index 164fc11cbffc8c466f84d51c07106b602d022bc6..884506a1bc58752669694df95c6dcb05726507a5 100644
--- a/src/bin/initdb/t/001_initdb.pl
+++ b/src/bin/initdb/t/001_initdb.pl
@@ -123,28 +123,41 @@ if ($ENV{with_icu} eq 'yes')
 		[
 			'initdb',                '--no-sync',
 			'--locale-provider=icu', '--encoding=SQL_ASCII',
-			'--icu-locale=en', "$tempdir/dataX"
+			"$tempdir/dataX"
 		],
 		qr/error: encoding mismatch/,
 		'fails for encoding not supported by ICU');
 }
 else
 {
-	command_fails(
+	command_fails_like(
 		[ 'initdb', '--no-sync', '--locale-provider=icu', "$tempdir/data2" ],
+		qr/error: ICU is not supported in this build/,
 		'locale provider ICU fails since no ICU support');
+
+	command_fails_like(
+		[
+			'initdb',                '--no-sync',
+			'--locale-provider=icu', '--encoding=SQL_ASCII',
+			"$tempdir/data2"
+		],
+		qr/error: ICU is not supported in this build/,
+		'locale provider ICU with not supported ICU encoding fails since no ICU support'
+	);
 }
 
-command_fails(
+command_fails_like(
 	[ 'initdb', '--no-sync', '--locale-provider=xyz', "$tempdir/dataX" ],
+	qr/error: unrecognized locale provider: xyz/,
 	'fails for invalid locale provider');
 
-command_fails(
+command_fails_like(
 	[
 		'initdb',                 '--no-sync',
 		'--locale-provider=libc', '--icu-locale=en',
 		"$tempdir/dataX"
 	],
+	qr/error: --icu-locale cannot be specified unless locale provider "icu" is chosen/,
 	'fails for invalid option combination');
 
 done_testing();
diff --git a/src/bin/scripts/t/020_createdb.pl b/src/bin/scripts/t/020_createdb.pl
index 8ed8628db11c1410db4987f11250535bfb1aa008..7a262d227061ace1f72498371ab0c4fa8767d7a9 100644
--- a/src/bin/scripts/t/020_createdb.pl
+++ b/src/bin/scripts/t/020_createdb.pl
@@ -30,11 +30,12 @@ if ($ENV{with_icu} eq 'yes')
 	# This fails because template0 uses libc provider and has no ICU
 	# locale set.  It would succeed if template0 used the icu
 	# provider.  XXX Maybe split into multiple tests?
-	$node->command_fails(
+	$node->command_fails_like(
 		[
 			'createdb', '-T', 'template0', '-E', 'UTF8',
 			'--locale-provider=icu', 'foobar4'
 		],
+		qr/ERROR:  ICU locale must be specified/,
 		'create database with ICU fails without ICU locale specified');
 
 	$node->issues_sql_like(
@@ -46,12 +47,13 @@ if ($ENV{with_icu} eq 'yes')
 		qr/statement: CREATE DATABASE foobar5 .* LOCALE_PROVIDER icu ICU_LOCALE 'en'/,
 		'create database with ICU locale specified');
 
-	$node->command_fails(
+	$node->command_fails_like(
 		[
 			'createdb', '-T', 'template0', '-E', 'UTF8',
 			'--locale-provider=icu',
 			'--icu-locale=@colNumeric=lower', 'foobarX'
 		],
+		qr/ERROR:  could not open collator for locale/,
 		'fails for invalid ICU locale');
 
 	$node->command_fails_like(
@@ -78,18 +80,39 @@ if ($ENV{with_icu} eq 'yes')
 }
 else
 {
-	$node->command_fails(
+	$node->command_fails_like(
 		[ 'createdb', '-T', 'template0', '--locale-provider=icu', 'foobar4' ],
+		qr/ERROR:  ICU is not supported in this build/,
 		'create database with ICU fails since no ICU support');
+
+	$node->command_fails_like(
+		[
+			'createdb',             '-T',
+			'template0',            '--locale-provider=icu',
+			'--encoding=SQL_ASCII', 'foobar4'
+		],
+		qr/ERROR:  ICU is not supported in this build/,
+		'create database with ICU and not supported ICU encoding fails since no ICU support'
+	);
 }
 
 $node->command_fails([ 'createdb', 'foobar1' ],
 	'fails if database already exists');
 
-$node->command_fails(
+$node->command_fails_like(
 	[ 'createdb', '-T', 'template0', '--locale-provider=xyz', 'foobarX' ],
+	qr/ERROR:  unrecognized locale provider: xyz/,
 	'fails for invalid locale provider');
 
+$node->command_fails_like(
+	[
+		'createdb',        '-T',
+		'template0',       '--locale-provider=libc',
+		'--icu-locale=en', 'foobarX'
+	],
+	qr/ERROR:  ICU locale cannot be specified unless locale provider is ICU/,
+	'fails for invalid option combination');
+
 # Check use of templates with shared dependencies copied from the template.
 my ($ret, $stdout, $stderr) = $node->psql(
 	'foobar2',
diff --git a/src/include/utils/pg_locale.h b/src/include/utils/pg_locale.h
index a87594212364aaac3337ef07188dd291d62299d7..6e8af399769fdb257a65446b3c476bbfeca49f33 100644
--- a/src/include/utils/pg_locale.h
+++ b/src/include/utils/pg_locale.h
@@ -104,8 +104,8 @@ extern char *get_collation_actual_version(char collprovider, const char *collcol
 #ifdef USE_ICU
 extern int32_t icu_to_uchar(UChar **buff_uchar, const char *buff, size_t nbytes);
 extern int32_t icu_from_uchar(char **result, const UChar *buff_uchar, int32_t len_uchar);
-#endif
 extern void check_icu_locale(const char *icu_locale);
+#endif
 
 /* These functions convert from/to libc's wchar_t, *not* pg_wchar_t */
 extern size_t wchar2char(char *to, const wchar_t *from, size_t tolen,

diff --git a/src/backend/commands/dbcommands.c b/src/backend/commands/dbcommands.c
index 96b46cbc020ef8b85b6d54d3d4ca8ad116277832..242d68f58287aeb6f95619c2ce8b78e38433cf18 100644
--- a/src/backend/commands/dbcommands.c
+++ b/src/backend/commands/dbcommands.c
@@ -1030,6 +1030,11 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 
 	if (dblocprovider == COLLPROVIDER_ICU)
 	{
+#ifndef USE_ICU
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				 errmsg("ICU is not supported in this build")));
+#else
 		if (!(is_encoding_supported_by_icu(encoding)))
 			ereport(ERROR,
 					(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
@@ -1046,6 +1051,7 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 					 errmsg("ICU locale must be specified")));
 
 		check_icu_locale(dbiculocale);
+#endif
 	}
 	else
 	{
diff --git a/src/backend/utils/adt/pg_locale.c b/src/backend/utils/adt/pg_locale.c
index 2b42d9ccd8b751bcb5cda3a1f4c7803a68bc0a4a..743f11e1d1fd62d500fc2846976472d13e08046b 100644
--- a/src/backend/utils/adt/pg_locale.c
+++ b/src/backend/utils/adt/pg_locale.c
@@ -1945,15 +1945,12 @@ icu_set_collation_attributes(UCollator *collator, const char *loc)
 	}
 }
 
-#endif							/* USE_ICU */
-
 /*
  * Check if the given locale ID is valid, and ereport(ERROR) if it isn't.
  */
 void
 check_icu_locale(const char *icu_locale)
 {
-#ifdef USE_ICU
 	UCollator  *collator;
 	UErrorCode	status;
 
@@ -1967,13 +1964,10 @@ check_icu_locale(const char *icu_locale)
 	if (U_ICU_VERSION_MAJOR_NUM < 54)
 		icu_set_collation_attributes(collator, icu_locale);
 	ucol_close(collator);
-#else
-	ereport(ERROR,
-			(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-			 errmsg("ICU is not supported in this build")));
-#endif
 }
 
+#endif							/* USE_ICU */
+
 /*
  * These functions convert from/to libc's wchar_t, *not* pg_wchar_t.
  * Therefore we keep them here rather than with the mbutils code.
diff --git a/src/bin/initdb/initdb.c b/src/bin/initdb/initdb.c
index f61a04305590c7d09ec59fe202d6f22c0a605827..47dde552e218055f5d73003799b4ccc7c96a49a7 100644
--- a/src/bin/initdb/initdb.c
+++ b/src/bin/initdb/initdb.c
@@ -2043,24 +2043,35 @@ check_locale_encoding(const char *locale, int user_enc)
 }
 
 /*
- * check if the chosen encoding matches is supported by ICU
+ * check if the chosen locale and encoding are supported by ICU
  *
  * this should match the similar check in the backend createdb() function
  */
-static bool
-check_icu_locale_encoding(int user_enc)
+static void
+check_icu_locale_encoding(void)
 {
-	if (!(is_encoding_supported_by_icu(user_enc)))
+#ifndef USE_ICU
+	pg_fatal("ICU is not supported in this build");
+#else
+	if (!(is_encoding_supported_by_icu(encodingid)))
 	{
 		pg_log_error("encoding mismatch");
 		pg_log_error_detail("The encoding you selected (%s) is not supported with the ICU provider.",
-							pg_encoding_to_char(user_enc));
+							pg_encoding_to_char(encodingid));
 		pg_log_error_hint("Rerun %s and either do not specify an encoding explicitly, "
 						  "or choose a matching combination.",
 						  progname);
-		return false;
+		exit(1);
 	}
-	return true;
+
+	if (!icu_locale)
+		pg_fatal("ICU locale must be specified");
+
+	/*
+	 * In supported builds, the ICU locale ID will be checked by the backend
+	 * during post-bootstrap initialization.
+	 */
+#endif
 }
 
 /*
@@ -2113,20 +2124,6 @@ setlocales(void)
 	check_locale_name(LC_CTYPE, lc_messages, &canonname);
 	lc_messages = canonname;
 #endif
-
-	if (locale_provider == COLLPROVIDER_ICU)
-	{
-		if (!icu_locale)
-			pg_fatal("ICU locale must be specified");
-
-		/*
-		 * In supported builds, the ICU locale ID will be checked by the
-		 * backend during post-bootstrap initialization.
-		 */
-#ifndef USE_ICU
-		pg_fatal("ICU is not supported in this build");
-#endif
-	}
 }
 
 /*
@@ -2297,18 +2294,86 @@ setup_bin_paths(const char *argv0)
 	canonicalize_path(share_path);
 }
 
+static void
+set_encoding(void)
+{
+	int			ctype_enc;
+
+	if (encoding)
+	{
+		encodingid = get_encoding_id(encoding);
+		return;
+	}
+
+	if (locale_provider == COLLPROVIDER_ICU)
+	{
+		encodingid = PG_UTF8;
+		printf(_("Encoding \"%s\" implied by locale will be set as the default database encoding.\n"),
+			   pg_encoding_to_char(encodingid));
+		return;
+	}
+
+	ctype_enc = pg_get_encoding_from_locale(lc_ctype, true);
+
+	if (ctype_enc == -1)
+	{
+		/* Couldn't recognize the locale's codeset */
+		pg_log_error("could not find suitable encoding for locale \"%s\"",
+					 lc_ctype);
+		pg_log_error_hint("Rerun %s with the -E option.", progname);
+		pg_log_error_hint("Try \"%s --help\" for more information.", progname);
+		exit(1);
+	}
+
+	if (!pg_valid_server_encoding_id(ctype_enc))
+	{
+		/*
+		 * We recognized it, but it's not a legal server encoding. On Windows,
+		 * UTF-8 works with any locale, so we can fall back to UTF-8.
+		 */
+#ifdef WIN32
+		encodingid = PG_UTF8;
+		printf(_("Encoding \"%s\" implied by locale is not allowed as a server-side encoding.\n"
+				 "The default database encoding will be set to \"%s\" instead.\n"),
+			   pg_encoding_to_char(ctype_enc),
+			   pg_encoding_to_char(encodingid));
+		return;
+#else
+		pg_log_error("locale \"%s\" requires unsupported encoding \"%s\"",
+					 lc_ctype, pg_encoding_to_char(ctype_enc));
+		pg_log_error_detail("Encoding \"%s\" is not allowed as a server-side encoding.",
+							pg_encoding_to_char(ctype_enc));
+		pg_log_error_hint("Rerun %s with a different locale selection.",
+						  progname);
+		exit(1);
+#endif
+	}
+
+	encodingid = ctype_enc;
+	printf(_("Encoding \"%s\" implied by locale will be set as the default database encoding.\n"),
+		   pg_encoding_to_char(encodingid));
+}
+
 void
 setup_locale_encoding(void)
 {
 	setlocales();
 
+	set_encoding();
+
+	if (!check_locale_encoding(lc_ctype, encodingid) ||
+		!check_locale_encoding(lc_collate, encodingid))
+		exit(1);				/* check_locale_encoding printed the error */
+
+	if (locale_provider == COLLPROVIDER_ICU)
+		check_icu_locale_encoding();
+
 	if (locale_provider == COLLPROVIDER_LIBC &&
 		strcmp(lc_ctype, lc_collate) == 0 &&
 		strcmp(lc_ctype, lc_time) == 0 &&
 		strcmp(lc_ctype, lc_numeric) == 0 &&
 		strcmp(lc_ctype, lc_monetary) == 0 &&
-		strcmp(lc_ctype, lc_messages) == 0 &&
-		(!icu_locale || strcmp(lc_ctype, icu_locale) == 0))
+		strcmp(lc_ctype, lc_messages) == 0)
 		printf(_("The database cluster will be initialized with locale \"%s\".\n"), lc_ctype);
 	else
 	{
@@ -2329,68 +2394,6 @@ setup_locale_encoding(void)
 			   lc_numeric,
 			   lc_time);
 	}
-
-	if (!encoding && locale_provider == COLLPROVIDER_ICU)
-	{
-		encodingid = PG_UTF8;
-		printf(_("The default database encoding has been set to \"%s\".\n"),
-			   pg_encoding_to_char(encodingid));
-	}
-	else if (!encoding)
-	{
-		int			ctype_enc;
-
-		ctype_enc = pg_get_encoding_from_locale(lc_ctype, true);
-
-		if (ctype_enc == -1)
-		{
-			/* Couldn't recognize the locale's codeset */
-			pg_log_error("could not find suitable encoding for locale \"%s\"",
-						 lc_ctype);
-			pg_log_error_hint("Rerun %s with the -E option.", progname);
-			pg_log_error_hint("Try \"%s --help\" for more information.", progname);
-			exit(1);
-		}
-		else if (!pg_valid_server_encoding_id(ctype_enc))
-		{
-			/*
-			 * We recognized it, but it's not a legal server encoding. On
-			 * Windows, UTF-8 works with any locale, so we can fall back to
-			 * UTF-8.
-			 */
-#ifdef WIN32
-			encodingid = PG_UTF8;
-			printf(_("Encoding \"%s\" implied by locale is not allowed as a server-side encoding.\n"
-					 "The default database encoding will be set to \"%s\" instead.\n"),
-				   pg_encoding_to_char(ctype_enc),
-				   pg_encoding_to_char(encodingid));
-#else
-			pg_log_error("locale \"%s\" requires unsupported encoding \"%s\"",
-						 lc_ctype, pg_encoding_to_char(ctype_enc));
-			pg_log_error_detail("Encoding \"%s\" is not allowed as a server-side encoding.",
-								pg_encoding_to_char(ctype_enc));
-			pg_log_error_hint("Rerun %s with a different locale selection.",
-							  progname);
-			exit(1);
-#endif
-		}
-		else
-		{
-			encodingid = ctype_enc;
-			printf(_("The default database encoding has accordingly been set to \"%s\".\n"),
-				   pg_encoding_to_char(encodingid));
-		}
-	}
-	else
-		encodingid = get_encoding_id(encoding);
-
-	if (!check_locale_encoding(lc_ctype, encodingid) ||
-		!check_locale_encoding(lc_collate, encodingid))
-		exit(1);				/* check_locale_encoding printed the error */
-
-	if (locale_provider == COLLPROVIDER_ICU &&
-		!check_icu_locale_encoding(encodingid))
-		exit(1);
 }
 
 
diff --git a/src/bin/initdb/t/001_initdb.pl b/src/bin/initdb/t/001_initdb.pl
index 164fc11cbffc8c466f84d51c07106b602d022bc6..3a5166408ce2ef7831d7bd80e1ec95cb8867517a 100644
--- a/src/bin/initdb/t/001_initdb.pl
+++ b/src/bin/initdb/t/001_initdb.pl
@@ -102,12 +102,14 @@ if ($ENV{with_icu} eq 'yes')
 		qr/initdb: error: ICU locale must be specified/,
 		'locale provider ICU requires --icu-locale');
 
-	command_ok(
+	command_like(
 		[
 			'initdb',                '--no-sync',
+			'-A',                    'trust',
 			'--locale-provider=icu', '--icu-locale=en',
 			"$tempdir/data3"
 		],
+		qr/Encoding "UTF8" implied by locale will be set as the default database encoding/,
 		'option --icu-locale');
 
 	command_fails_like(
@@ -123,28 +125,41 @@ if ($ENV{with_icu} eq 'yes')
 		[
 			'initdb',                '--no-sync',
 			'--locale-provider=icu', '--encoding=SQL_ASCII',
-			'--icu-locale=en', "$tempdir/dataX"
+			"$tempdir/dataX"
 		],
 		qr/error: encoding mismatch/,
 		'fails for encoding not supported by ICU');
 }
 else
 {
-	command_fails(
+	command_fails_like(
 		[ 'initdb', '--no-sync', '--locale-provider=icu', "$tempdir/data2" ],
+		qr/error: ICU is not supported in this build/,
 		'locale provider ICU fails since no ICU support');
+
+	command_fails_like(
+		[
+			'initdb',                '--no-sync',
+			'--locale-provider=icu', '--encoding=SQL_ASCII',
+			"$tempdir/data2"
+		],
+		qr/error: ICU is not supported in this build/,
+		'locale provider ICU with not supported ICU encoding fails since no ICU support'
+	);
 }
 
-command_fails(
+command_fails_like(
 	[ 'initdb', '--no-sync', '--locale-provider=xyz', "$tempdir/dataX" ],
+	qr/error: unrecognized locale provider: xyz/,
 	'fails for invalid locale provider');
 
-command_fails(
+command_fails_like(
 	[
 		'initdb',                 '--no-sync',
 		'--locale-provider=libc', '--icu-locale=en',
 		"$tempdir/dataX"
 	],
+	qr/error: --icu-locale cannot be specified unless locale provider "icu" is chosen/,
 	'fails for invalid option combination');
 
 done_testing();
diff --git a/src/bin/scripts/t/020_createdb.pl b/src/bin/scripts/t/020_createdb.pl
index a74bf3b0d8bb9642d0b24f5781d5794727466a88..45b44fce460376240a2617fa207e44e686439fab 100644
--- a/src/bin/scripts/t/020_createdb.pl
+++ b/src/bin/scripts/t/020_createdb.pl
@@ -30,11 +30,12 @@ if ($ENV{with_icu} eq 'yes')
 	# This fails because template0 uses libc provider and has no ICU
 	# locale set.  It would succeed if template0 used the icu
 	# provider.  XXX Maybe split into multiple tests?
-	$node->command_fails(
+	$node->command_fails_like(
 		[
 			'createdb', '-T', 'template0', '-E', 'UTF8',
 			'--locale-provider=icu', 'foobar4'
 		],
+		qr/ERROR:  ICU locale must be specified/,
 		'create database with ICU fails without ICU locale specified');
 
 	$node->issues_sql_like(
@@ -46,12 +47,13 @@ if ($ENV{with_icu} eq 'yes')
 		qr/statement: CREATE DATABASE foobar5 .* LOCALE_PROVIDER icu ICU_LOCALE 'en'/,
 		'create database with ICU locale specified');
 
-	$node->command_fails(
+	$node->command_fails_like(
 		[
 			'createdb', '-T', 'template0', '-E', 'UTF8',
 			'--locale-provider=icu',
 			'--icu-locale=@colNumeric=lower', 'foobarX'
 		],
+		qr/ERROR:  could not open collator for locale/,
 		'fails for invalid ICU locale');
 
 	$node->command_fails_like(
@@ -78,18 +80,39 @@ if ($ENV{with_icu} eq 'yes')
 }
 else
 {
-	$node->command_fails(
+	$node->command_fails_like(
 		[ 'createdb', '-T', 'template0', '--locale-provider=icu', 'foobar4' ],
+		qr/ERROR:  ICU is not supported in this build/,
 		'create database with ICU fails since no ICU support');
+
+	$node->command_fails_like(
+		[
+			'createdb',             '-T',
+			'template0',            '--locale-provider=icu',
+			'--encoding=SQL_ASCII', 'foobar4'
+		],
+		qr/ERROR:  ICU is not supported in this build/,
+		'create database with ICU and not supported ICU encoding fails since no ICU support'
+	);
 }
 
 $node->command_fails([ 'createdb', 'foobar1' ],
 	'fails if database already exists');
 
-$node->command_fails(
+$node->command_fails_like(
 	[ 'createdb', '-T', 'template0', '--locale-provider=xyz', 'foobarX' ],
+	qr/ERROR:  unrecognized locale provider: xyz/,
 	'fails for invalid locale provider');
 
+$node->command_fails_like(
+	[
+		'createdb',        '-T',
+		'template0',       '--locale-provider=libc',
+		'--icu-locale=en', 'foobarX'
+	],
+	qr/ERROR:  ICU locale cannot be specified unless locale provider is ICU/,
+	'fails for invalid option combination');
+
 # Check use of templates with shared dependencies copied from the template.
 my ($ret, $stdout, $stderr) = $node->psql(
 	'foobar2',
diff --git a/src/include/utils/pg_locale.h b/src/include/utils/pg_locale.h
index a87594212364aaac3337ef07188dd291d62299d7..6e8af399769fdb257a65446b3c476bbfeca49f33 100644
--- a/src/include/utils/pg_locale.h
+++ b/src/include/utils/pg_locale.h
@@ -104,8 +104,8 @@ extern char *get_collation_actual_version(char collprovider, const char *collcol
 #ifdef USE_ICU
 extern int32_t icu_to_uchar(UChar **buff_uchar, const char *buff, size_t nbytes);
 extern int32_t icu_from_uchar(char **result, const UChar *buff_uchar, int32_t len_uchar);
-#endif
 extern void check_icu_locale(const char *icu_locale);
+#endif
 
 /* These functions convert from/to libc's wchar_t, *not* pg_wchar_t */
 extern size_t wchar2char(char *to, const wchar_t *from, size_t tolen,

diff --git a/src/backend/access/hash/hashfunc.c b/src/backend/access/hash/hashfunc.c
index b57ed946c42bb54ede800e95045aa937a8dbad85..b3c0f6f753f8428274389844ccf9778a7ed47ea4 100644
--- a/src/backend/access/hash/hashfunc.c
+++ b/src/backend/access/hash/hashfunc.c
@@ -281,6 +281,14 @@ hashtext(PG_FUNCTION_ARGS)
 	if (!lc_collate_is_c(collid))
 		mylocale = pg_newlocale_from_collation(collid);
 
+	elog(NOTICE, "hashtext lc_collate_is_c(collid) %d mylocale %p", lc_collate_is_c(collid), mylocale);
+	if (mylocale)
+	{
+		elog(NOTICE, "hashtext mylocale->provider %c", mylocale->provider);
+		if (mylocale->provider == COLLPROVIDER_ICU)
+			elog(NOTICE, "hashtext mylocale->info.icu.locale %s", mylocale->info.icu.locale ? mylocale->info.icu.locale : "(null)");
+	}
+
 	if (!mylocale || mylocale->deterministic)
 	{
 		result = hash_any((unsigned char *) VARDATA_ANY(key),
@@ -337,6 +345,14 @@ hashtextextended(PG_FUNCTION_ARGS)
 	if (!lc_collate_is_c(collid))
 		mylocale = pg_newlocale_from_collation(collid);
 
+	elog(NOTICE, "hashtextextended lc_collate_is_c(collid) %d mylocale %p", lc_collate_is_c(collid), mylocale);
+	if (mylocale)
+	{
+		elog(NOTICE, "hashtextextended mylocale->provider %c", mylocale->provider);
+		if (mylocale->provider == COLLPROVIDER_ICU)
+			elog(NOTICE, "hashtextextended mylocale->info.icu.locale %s", mylocale->info.icu.locale ? mylocale->info.icu.locale : "(null)");
+	}
+
 	if (!mylocale || mylocale->deterministic)
 	{
 		result = hash_any_extended((unsigned char *) VARDATA_ANY(key),
diff --git a/src/backend/regex/regc_pg_locale.c b/src/backend/regex/regc_pg_locale.c
index 02d462a659778016f3c4479d425ba0a84feb6e26..9627c84a7ccfb4c4013556a51c989e9e6d611634 100644
--- a/src/backend/regex/regc_pg_locale.c
+++ b/src/backend/regex/regc_pg_locale.c
@@ -243,6 +243,8 @@ pg_set_regex_collation(Oid collation)
 				 errhint("Use the COLLATE clause to set the collation explicitly.")));
 	}
 
+	elog(NOTICE, "pg_set_regex_collation lc_ctype_is_c(collid) %d", lc_ctype_is_c(collation));
+
 	if (lc_ctype_is_c(collation))
 	{
 		/* C/POSIX collations use this path regardless of database encoding */
@@ -259,6 +261,14 @@ pg_set_regex_collation(Oid collation)
 		 */
 		pg_regex_locale = pg_newlocale_from_collation(collation);
 
+		elog(NOTICE, "pg_set_regex_collation pg_regex_locale %p", pg_regex_locale);
+		if (pg_regex_locale)
+		{
+			elog(NOTICE, "pg_set_regex_collation pg_regex_locale->provider %c", pg_regex_locale->provider);
+			if (pg_regex_locale->provider == COLLPROVIDER_ICU)
+				elog(NOTICE, "pg_set_regex_collation pg_regex_locale->info.icu.locale %s", pg_regex_locale->info.icu.locale ? pg_regex_locale->info.icu.locale : "(null)");
+		}
+
 		if (pg_regex_locale && !pg_regex_locale->deterministic)
 			ereport(ERROR,
 					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
diff --git a/src/backend/utils/adt/formatting.c b/src/backend/utils/adt/formatting.c
index 26f498b5df4d8eb280a0e6af69fd92d4ce0d89b7..a0616a0457c9abe4635064964146027008271ff8 100644
--- a/src/backend/utils/adt/formatting.c
+++ b/src/backend/utils/adt/formatting.c
@@ -1682,6 +1682,8 @@ str_tolower(const char *buff, size_t nbytes, Oid collid)
 				 errhint("Use the COLLATE clause to set the collation explicitly.")));
 	}
 
+	elog(NOTICE, "str_tolower lc_ctype_is_c(collid) %d", lc_ctype_is_c(collid));
+
 	/* C/POSIX collations use this path regardless of database encoding */
 	if (lc_ctype_is_c(collid))
 	{
@@ -1693,6 +1695,14 @@ str_tolower(const char *buff, size_t nbytes, Oid collid)
 
 		mylocale = pg_newlocale_from_collation(collid);
 
+		elog(NOTICE, "str_tolower mylocale %p", mylocale);
+		if (mylocale)
+		{
+			elog(NOTICE, "str_tolower mylocale->provider %c", mylocale->provider);
+			if (mylocale->provider == COLLPROVIDER_ICU)
+				elog(NOTICE, "str_tolower mylocale->info.icu.locale %s", mylocale->info.icu.locale ? mylocale->info.icu.locale : "(null)");
+		}
+
 #ifdef USE_ICU
 		if (mylocale && mylocale->provider == COLLPROVIDER_ICU)
 		{
@@ -1804,6 +1814,8 @@ str_toupper(const char *buff, size_t nbytes, Oid collid)
 				 errhint("Use the COLLATE clause to set the collation explicitly.")));
 	}
 
+	elog(NOTICE, "str_toupper lc_ctype_is_c(collid) %d", lc_ctype_is_c(collid));
+
 	/* C/POSIX collations use this path regardless of database encoding */
 	if (lc_ctype_is_c(collid))
 	{
@@ -1815,6 +1827,14 @@ str_toupper(const char *buff, size_t nbytes, Oid collid)
 
 		mylocale = pg_newlocale_from_collation(collid);
 
+		elog(NOTICE, "str_toupper mylocale %p", mylocale);
+		if (mylocale)
+		{
+			elog(NOTICE, "str_toupper mylocale->provider %c", mylocale->provider);
+			if (mylocale->provider == COLLPROVIDER_ICU)
+				elog(NOTICE, "str_toupper mylocale->info.icu.locale %s", mylocale->info.icu.locale ? mylocale->info.icu.locale : "(null)");
+		}
+
 #ifdef USE_ICU
 		if (mylocale && mylocale->provider == COLLPROVIDER_ICU)
 		{
@@ -1927,6 +1947,8 @@ str_initcap(const char *buff, size_t nbytes, Oid collid)
 				 errhint("Use the COLLATE clause to set the collation explicitly.")));
 	}
 
+	elog(NOTICE, "str_initcap lc_ctype_is_c(collid) %d", lc_ctype_is_c(collid));
+
 	/* C/POSIX collations use this path regardless of database encoding */
 	if (lc_ctype_is_c(collid))
 	{
@@ -1938,6 +1960,14 @@ str_initcap(const char *buff, size_t nbytes, Oid collid)
 
 		mylocale = pg_newlocale_from_collation(collid);
 
+		elog(NOTICE, "str_initcap mylocale %p", mylocale);
+		if (mylocale)
+		{
+			elog(NOTICE, "str_initcap mylocale->provider %c", mylocale->provider);
+			if (mylocale->provider == COLLPROVIDER_ICU)
+				elog(NOTICE, "str_initcap mylocale->info.icu.locale %s", mylocale->info.icu.locale ? mylocale->info.icu.locale : "(null)");
+		}
+
 #ifdef USE_ICU
 		if (mylocale && mylocale->provider == COLLPROVIDER_ICU)
 		{
diff --git a/src/backend/utils/adt/varchar.c b/src/backend/utils/adt/varchar.c
index 68e2e6f7a719866eacc506e1780f6d1b58951599..dacf044a4ee05555b4742300d0c078b3880db60c 100644
--- a/src/backend/utils/adt/varchar.c
+++ b/src/backend/utils/adt/varchar.c
@@ -1010,6 +1010,14 @@ hashbpchar(PG_FUNCTION_ARGS)
 	if (!lc_collate_is_c(collid))
 		mylocale = pg_newlocale_from_collation(collid);
 
+	elog(NOTICE, "hashbpchar lc_collate_is_c(collid) %d mylocale %p", lc_collate_is_c(collid), mylocale);
+	if (mylocale)
+	{
+		elog(NOTICE, "hashbpchar mylocale->provider %c", mylocale->provider);
+		if (mylocale->provider == COLLPROVIDER_ICU)
+			elog(NOTICE, "hashbpchar mylocale->info.icu.locale %s", mylocale->info.icu.locale ? mylocale->info.icu.locale : "(null)");
+	}
+
 	if (!mylocale || mylocale->deterministic)
 	{
 		result = hash_any((unsigned char *) keydata, keylen);
@@ -1070,6 +1078,14 @@ hashbpcharextended(PG_FUNCTION_ARGS)
 	if (!lc_collate_is_c(collid))
 		mylocale = pg_newlocale_from_collation(collid);
 
+	elog(NOTICE, "hashbpcharextended lc_collate_is_c(collid) %d mylocale %p", lc_collate_is_c(collid), mylocale);
+	if (mylocale)
+	{
+		elog(NOTICE, "hashbpcharextended mylocale->provider %c", mylocale->provider);
+		if (mylocale->provider == COLLPROVIDER_ICU)
+			elog(NOTICE, "hashbpcharextended mylocale->info.icu.locale %s", mylocale->info.icu.locale ? mylocale->info.icu.locale : "(null)");
+	}
+
 	if (!mylocale || mylocale->deterministic)
 	{
 		result = hash_any_extended((unsigned char *) keydata, keylen,
diff --git a/src/backend/utils/adt/varlena.c b/src/backend/utils/adt/varlena.c
index c5e7ee7ca2d3073c067928cfa35c1e746218bb64..012565dd2986c7ae9781f61dbb5f724770575fab 100644
--- a/src/backend/utils/adt/varlena.c
+++ b/src/backend/utils/adt/varlena.c
@@ -1521,6 +1521,8 @@ varstr_cmp(const char *arg1, int len1, const char *arg2, int len2, Oid collid)
 
 	check_collation_set(collid);
 
+	elog(NOTICE, "varstr_cmp lc_collate_is_c(collid) %d", lc_collate_is_c(collid));
+
 	/*
 	 * Unfortunately, there is no strncoll(), so in the non-C locale case we
 	 * have to do some memory copying.  This turns out to be significantly
@@ -1543,6 +1545,14 @@ varstr_cmp(const char *arg1, int len1, const char *arg2, int len2, Oid collid)
 
 		mylocale = pg_newlocale_from_collation(collid);
 
+		elog(NOTICE, "varstr_cmp mylocale %p", mylocale);
+		if (mylocale)
+		{
+			elog(NOTICE, "varstr_cmp mylocale->provider %c", mylocale->provider);
+			if (mylocale->provider == COLLPROVIDER_ICU)
+				elog(NOTICE, "varstr_cmp mylocale->info.icu.locale %s", mylocale->info.icu.locale ? mylocale->info.icu.locale : "(null)");
+		}
+
 		/*
 		 * memcmp() can't tell us which of two unequal strings sorts first,
 		 * but it's a cheap way to tell if they're equal.  Testing shows that
@@ -2377,6 +2387,14 @@ varstrfastcmp_locale(char *a1p, int len1, char *a2p, int len2, SortSupport ssup)
 		return sss->last_returned;
 	}
 
+	elog(NOTICE, "varstrfastcmp_locale sss->collate_c %d sss->locale %p", sss->collate_c, sss->locale);
+	if (sss->locale)
+	{
+		elog(NOTICE, "varstrfastcmp_locale sss->locale->provider %c", sss->locale->provider);
+		if (sss->locale->provider == COLLPROVIDER_ICU)
+			elog(NOTICE, "varstrfastcmp_locale sss->locale->info.icu.locale %s", sss->locale->info.icu.locale ? sss->locale->info.icu.locale : "(null)");
+	}
+
 	if (sss->locale)
 	{
 		if (sss->locale->provider == COLLPROVIDER_ICU)
@@ -2472,6 +2490,14 @@ varstr_abbrev_convert(Datum original, SortSupport ssup)
 	if (sss->typid == BPCHAROID)
 		len = bpchartruelen(authoritative_data, len);
 
+	elog(NOTICE, "varstr_abbrev_convert sss->collate_c %d sss->locale %p", sss->collate_c, sss->locale);
+	if (sss->locale)
+	{
+		elog(NOTICE, "varstr_abbrev_convert sss->locale->provider %c", sss->locale->provider);
+		if (sss->locale->provider == COLLPROVIDER_ICU)
+			elog(NOTICE, "varstr_abbrev_convert sss->locale->info.icu.locale %s", sss->locale->info.icu.locale ? sss->locale->info.icu.locale : "(null)");
+	}
+
 	/*
 	 * If we're using the C collation, use memcpy(), rather than strxfrm(), to
 	 * abbreviate keys.  The full comparator for the C locale is always

diff --git a/src/test/regress/pg_regress.c b/src/test/regress/pg_regress.c
index dda076847a38a74a765ca1283226815e9d10ada1..4aa42c6b1c7f2f2c36af539bafca4d64cdb7db3a 100644
--- a/src/test/regress/pg_regress.c
+++ b/src/test/regress/pg_regress.c
@@ -1899,14 +1899,25 @@ create_database(const char *dbname)
 	/*
 	 * We use template0 so that any installation-local cruft in template1 will
 	 * not mess up the tests.
+	 *
+	 * Explicitly set the locale provider libc for the option --no-locale.
+	 * Otherwise during installcheck the new database may use the ICU locale
+	 * provider with the custom ICU locale from template0.
 	 */
 	header(_("creating database \"%s\""), dbname);
 	if (encoding)
+
+		/*
+		 * Explicitly set the locale provider libc for the manually chosen
+		 * encoding. Otherwise during installcheck the new database may use
+		 * the ICU locale provider (from template0) which does not support all
+		 * encodings.
+		 */
 		psql_add_command(buf, "CREATE DATABASE \"%s\" TEMPLATE=template0 ENCODING='%s'%s", dbname, encoding,
-						 (nolocale) ? " LC_COLLATE='C' LC_CTYPE='C'" : "");
+						 (nolocale) ? " LC_COLLATE='C' LC_CTYPE='C' LOCALE_PROVIDER='libc'" : " LOCALE_PROVIDER='libc'");
 	else
 		psql_add_command(buf, "CREATE DATABASE \"%s\" TEMPLATE=template0%s", dbname,
-						 (nolocale) ? " LC_COLLATE='C' LC_CTYPE='C'" : "");
+						 (nolocale) ? " LC_COLLATE='C' LC_CTYPE='C' LOCALE_PROVIDER='libc'" : "");
 	psql_add_command(buf,
 					 "ALTER DATABASE \"%s\" SET lc_messages TO 'C';"
 					 "ALTER DATABASE \"%s\" SET lc_monetary TO 'C';"