TRUNCATE on foreign tables

 contrib/postgres_fdw/deparse.c                 | 10 +++
 contrib/postgres_fdw/expected/postgres_fdw.out | 89 ++++++++++++++++++++++++++
 contrib/postgres_fdw/postgres_fdw.c            | 31 +++++++++
 contrib/postgres_fdw/postgres_fdw.h            |  1 +
 contrib/postgres_fdw/sql/postgres_fdw.sql      | 31 +++++++++
 doc/src/sgml/fdwhandler.sgml                   | 26 ++++++++
 src/backend/commands/tablecmds.c               | 28 ++++++--
 src/include/foreign/fdwapi.h                   |  5 ++
 8 files changed, 217 insertions(+), 4 deletions(-)

diff --git a/contrib/postgres_fdw/deparse.c b/contrib/postgres_fdw/deparse.c
index e803997..99d6a05 100644
--- a/contrib/postgres_fdw/deparse.c
+++ b/contrib/postgres_fdw/deparse.c
@@ -2099,6 +2099,16 @@ deparseAnalyzeSql(StringInfo buf, Relation rel, List **retrieved_attrs)
 }
 
 /*
+ * Construct a simple "TRUNCATE rel" statement
+ */
+void
+deparseTruncateSql(StringInfo buf, Relation rel)
+{
+	appendStringInfoString(buf, "TRUNCATE ");
+	deparseRelation(buf, rel);
+}
+
+/*
  * Construct name to use for given column, and emit it into buf.
  * If it has a column_name FDW option, use that instead of attribute name.
  *
diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index c915885..2a494f8 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8157,6 +8157,95 @@ select * from rem3;
 drop foreign table rem3;
 drop table loc3;
 -- ===================================================================
+-- test for TRUNCATE
+-- ===================================================================
+CREATE TABLE tru_nt (id int, x text);
+CREATE FOREIGN TABLE tru_ft (id int, x text)
+       SERVER loopback OPTIONS (table_name 'tru_nt');
+INSERT INTO tru_nt (SELECT x,md5(x::text) FROM generate_series(1,10) x);
+CREATE TABLE tru_pt (id int, y text) PARTITION BY HASH(id);
+CREATE TABLE tru_pt__p0 PARTITION OF tru_pt
+                        FOR VALUES WITH (MODULUS 2, REMAINDER 0);
+CREATE TABLE __tru_pt__p1 (id int, y text);
+CREATE FOREIGN TABLE tru_pt__p1 PARTITION OF tru_pt
+                                FOR VALUES WITH (MODULUS 2, REMAINDER 1)
+               SERVER loopback OPTIONS (table_name '__tru_pt__p1');
+INSERT INTO tru_pt (SELECT x,md5(x::text) FROM generate_series(11,30) x);
+-- normal truncate
+SELECT * FROM tru_ft;
+ id |                x                 
+----+----------------------------------
+  1 | c4ca4238a0b923820dcc509a6f75849b
+  2 | c81e728d9d4c2f636f067f89cc14862c
+  3 | eccbc87e4b5ce2fe28308fd9f2a7baf3
+  4 | a87ff679a2f3e71d9181a67b7542122c
+  5 | e4da3b7fbbce2345d7772b0674a318d5
+  6 | 1679091c5a880faf6fb5e6087eb1b2dc
+  7 | 8f14e45fceea167a5a36dedd4bea2543
+  8 | c9f0f895fb98ab9159f51fd0297e236d
+  9 | 45c48cce2e2d7fbdea1afc51c7c6ad26
+ 10 | d3d9446802a44259755d38e6d163e820
+(10 rows)
+
+TRUNCATE tru_ft;
+SELECT * FROM tru_nt;
+ id | x 
+----+---
+(0 rows)
+
+SELECT * FROM tru_ft;
+ id | x 
+----+---
+(0 rows)
+
+-- partition table mixtured by table and foreign table
+SELECT * FROM tru_pt;
+ id |                y                 
+----+----------------------------------
+ 12 | c20ad4d76fe97759aa27a0c99bff6710
+ 13 | c51ce410c124a10e0db5e4b97fc2af39
+ 14 | aab3238922bcc25a6f606eb525ffdc56
+ 16 | c74d97b01eae257e44aa9d5bade97baf
+ 17 | 70efdf2ec9b086079795c442636b55fb
+ 18 | 6f4922f45568161a8cdf4ad2299f6d23
+ 23 | 37693cfc748049e45d87b8c7d8b9aacd
+ 25 | 8e296a067a37563370ded05f5a3bf3ec
+ 26 | 4e732ced3463d06de0ca9a15b6153677
+ 27 | 02e74f10e0327ad868d138f2b4fdd6f0
+ 28 | 33e75ff09dd601bbe69f351039152189
+ 30 | 34173cb38f07f89ddbebc2ac9128303f
+ 11 | 6512bd43d9caa6e02c990b0a82652dca
+ 15 | 9bf31c7ff062936a96d3c8bd1f8f2ff3
+ 19 | 1f0e3dad99908345f7439f8ffabdffc4
+ 20 | 98f13708210194c475687be6106a3b84
+ 21 | 3c59dc048e8850243be8079a5c74d079
+ 22 | b6d767d2f8ed5d21a44b0e5886680cb9
+ 24 | 1ff1de774005f8da13f42943881c655f
+ 29 | 6ea9ab1baa0efb9e19094440c317e21b
+(20 rows)
+
+TRUNCATE tru_pt;
+SELECT * FROM tru_pt;
+ id | y 
+----+---
+(0 rows)
+
+SELECT * FROM tru_pt__p0;
+ id | y 
+----+---
+(0 rows)
+
+SELECT * FROM tru_pt__p1;
+ id | y 
+----+---
+(0 rows)
+
+SELECT * FROM __tru_pt__p1;
+ id | y 
+----+---
+(0 rows)
+
+-- ===================================================================
 -- test IMPORT FOREIGN SCHEMA
 -- ===================================================================
 CREATE SCHEMA import_source;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index bdc21b3..9fd8bc7 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -373,6 +373,7 @@ static void postgresExplainForeignModify(ModifyTableState *mtstate,
 										 ExplainState *es);
 static void postgresExplainDirectModify(ForeignScanState *node,
 										ExplainState *es);
+static void postgresExecForeignTruncate(Relation relation);
 static bool postgresAnalyzeForeignTable(Relation relation,
 										AcquireSampleRowsFunc *func,
 										BlockNumber *totalpages);
@@ -546,6 +547,9 @@ postgres_fdw_handler(PG_FUNCTION_ARGS)
 	routine->ExplainForeignModify = postgresExplainForeignModify;
 	routine->ExplainDirectModify = postgresExplainDirectModify;
 
+	/* Support function for TRUNCATE */
+	routine->ExecForeignTruncate = postgresExecForeignTruncate;
+
 	/* Support functions for ANALYZE */
 	routine->AnalyzeForeignTable = postgresAnalyzeForeignTable;
 
@@ -2656,6 +2660,33 @@ postgresExplainDirectModify(ForeignScanState *node, ExplainState *es)
 	}
 }
 
+/*
+ * postgresExecForeignTruncate
+ *		It propagates TRUNCATE command to the remote host inside of the
+ *		transaction block.
+ */
+static void
+postgresExecForeignTruncate(Relation frel)
+{
+	ForeignTable   *ft = GetForeignTable(RelationGetRelid(frel));
+	UserMapping	   *user = GetUserMapping(GetUserId(), ft->serverid);
+	PGconn		   *conn = GetConnection(user, false);
+	PGresult	   *res;
+	StringInfoData	sql;
+
+	/* set up remote query */
+	initStringInfo(&sql);
+	deparseTruncateSql(&sql, frel);
+
+	if (!PQsendQuery(conn, sql.data))
+		pgfdw_report_error(ERROR, NULL, conn, false, sql.data);
+	res = pgfdw_get_result(conn, sql.data);
+	if (PQresultStatus(res) != PGRES_COMMAND_OK)
+		pgfdw_report_error(ERROR, res, conn, true, sql.data);
+	/* clean-up */
+	PQclear(res);
+	pfree(sql.data);
+}
 
 /*
  * estimate_path_cost_size
diff --git a/contrib/postgres_fdw/postgres_fdw.h b/contrib/postgres_fdw/postgres_fdw.h
index ea05287..a055ad7 100644
--- a/contrib/postgres_fdw/postgres_fdw.h
+++ b/contrib/postgres_fdw/postgres_fdw.h
@@ -190,6 +190,7 @@ extern void deparseDirectDeleteSql(StringInfo buf, PlannerInfo *root,
 extern void deparseAnalyzeSizeSql(StringInfo buf, Relation rel);
 extern void deparseAnalyzeSql(StringInfo buf, Relation rel,
 							  List **retrieved_attrs);
+extern void deparseTruncateSql(StringInfo buf, Relation rel);
 extern void deparseStringLiteral(StringInfo buf, const char *val);
 extern Expr *find_em_expr_for_rel(EquivalenceClass *ec, RelOptInfo *rel);
 extern Expr *find_em_expr_for_input_target(PlannerInfo *root,
diff --git a/contrib/postgres_fdw/sql/postgres_fdw.sql b/contrib/postgres_fdw/sql/postgres_fdw.sql
index 4f29e7c..0b6a48d 100644
--- a/contrib/postgres_fdw/sql/postgres_fdw.sql
+++ b/contrib/postgres_fdw/sql/postgres_fdw.sql
@@ -2275,6 +2275,37 @@ drop foreign table rem3;
 drop table loc3;
 
 -- ===================================================================
+-- test for TRUNCATE
+-- ===================================================================
+CREATE TABLE tru_nt (id int, x text);
+CREATE FOREIGN TABLE tru_ft (id int, x text)
+       SERVER loopback OPTIONS (table_name 'tru_nt');
+INSERT INTO tru_nt (SELECT x,md5(x::text) FROM generate_series(1,10) x);
+
+CREATE TABLE tru_pt (id int, y text) PARTITION BY HASH(id);
+CREATE TABLE tru_pt__p0 PARTITION OF tru_pt
+                        FOR VALUES WITH (MODULUS 2, REMAINDER 0);
+CREATE TABLE __tru_pt__p1 (id int, y text);
+CREATE FOREIGN TABLE tru_pt__p1 PARTITION OF tru_pt
+                                FOR VALUES WITH (MODULUS 2, REMAINDER 1)
+               SERVER loopback OPTIONS (table_name '__tru_pt__p1');
+INSERT INTO tru_pt (SELECT x,md5(x::text) FROM generate_series(11,30) x);
+
+-- normal truncate
+SELECT * FROM tru_ft;
+TRUNCATE tru_ft;
+SELECT * FROM tru_nt;
+SELECT * FROM tru_ft;
+
+-- partition table mixtured by table and foreign table
+SELECT * FROM tru_pt;
+TRUNCATE tru_pt;
+SELECT * FROM tru_pt;
+SELECT * FROM tru_pt__p0;
+SELECT * FROM tru_pt__p1;
+SELECT * FROM __tru_pt__p1;
+
+-- ===================================================================
 -- test IMPORT FOREIGN SCHEMA
 -- ===================================================================
 
diff --git a/doc/src/sgml/fdwhandler.sgml b/doc/src/sgml/fdwhandler.sgml
index 6587678..ad91768 100644
--- a/doc/src/sgml/fdwhandler.sgml
+++ b/doc/src/sgml/fdwhandler.sgml
@@ -968,6 +968,32 @@ EndDirectModify(ForeignScanState *node);
 
    </sect2>
 
+   <sect2 id="fdw-callbacks-truncate">
+    <title>FDW Routines for Truncate</title>
+<programlisting>
+void
+ExecForeignTruncate(Relation frel);
+</programlisting>
+    <para>
+     Executes remote truncate on the remote relation associated with this
+     foreign table. This optional function is called during execution of
+     <command>TRUNCATE</command>.
+
+     If FDW does not provide this callback, PostgreSQL considers
+     <command>TRUNCATE</command> is not supported on the foreign table.
+    </para>
+    <para>
+     Pay attention that <command>TRUNCATE</command> can be transaction-safe
+     in <productname>PostgreSQL</productname>.
+     We can revert the <command>TRUNCATE</command> operation unless current
+     transaction is not committed, however, it is not true on some other
+     database products.
+     If FDW author considers to support <command>TRUNCATE</command> on their
+     FDW driver, it may not be sufficient just to run a
+     <command>TRUNCATE</command> command on the remote side.
+    </para>
+   </sect2>
+
    <sect2 id="fdw-callbacks-row-locking">
     <title>FDW Routines for Row Locking</title>
 
diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index e19772a..1312b24 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -60,6 +60,7 @@
 #include "commands/user.h"
 #include "executor/executor.h"
 #include "foreign/foreign.h"
+#include "foreign/fdwapi.h"
 #include "miscadmin.h"
 #include "nodes/makefuncs.h"
 #include "nodes/nodeFuncs.h"
@@ -1765,6 +1766,14 @@ ExecuteTruncateGuts(List *explicit_rels, List *relids, List *relids_logged,
 		/* Skip partitioned tables as there is nothing to do */
 		if (rel->rd_rel->relkind == RELKIND_PARTITIONED_TABLE)
 			continue;
+		/* FDW driver runs its "TRUNCATE" implementation */
+		if (rel->rd_rel->relkind == RELKIND_FOREIGN_TABLE)
+		{
+			FdwRoutine *fdwroutine = GetFdwRoutineForRelation(rel, false);
+
+			fdwroutine->ExecForeignTruncate(rel);
+			continue;
+		}
 
 		/*
 		 * Normally, we need a transaction-safe truncation here.  However, if
@@ -1913,12 +1922,23 @@ truncate_check_rel(Oid relid, Form_pg_class reltuple)
 	char	   *relname = NameStr(reltuple->relname);
 
 	/*
-	 * Only allow truncate on regular tables and partitioned tables (although,
+	 * Only allow truncate on regular tables, partitioned tables (although,
 	 * the latter are only being included here for the following checks; no
-	 * physical truncation will occur in their case.)
+	 * physical truncation will occur in their case.) and foreign tables
+	 * that support ExecForeignTruncate callback.
 	 */
-	if (reltuple->relkind != RELKIND_RELATION &&
-		reltuple->relkind != RELKIND_PARTITIONED_TABLE)
+	if (reltuple->relkind == RELKIND_FOREIGN_TABLE)
+	{
+		FdwRoutine *fdwroutine = GetFdwRoutineByRelId(relid);
+
+		if (!fdwroutine->ExecForeignTruncate)
+			ereport(ERROR,
+					(errcode(ERRCODE_WRONG_OBJECT_TYPE),
+					 errmsg("\"%s\" is not a supported foreign table",
+							relname)));
+	}
+	else if (reltuple->relkind != RELKIND_RELATION &&
+			 reltuple->relkind != RELKIND_PARTITIONED_TABLE)
 		ereport(ERROR,
 				(errcode(ERRCODE_WRONG_OBJECT_TYPE),
 				 errmsg("\"%s\" is not a table", relname)));
diff --git a/src/include/foreign/fdwapi.h b/src/include/foreign/fdwapi.h
index 8226860..20adfb5 100644
--- a/src/include/foreign/fdwapi.h
+++ b/src/include/foreign/fdwapi.h
@@ -118,6 +118,8 @@ typedef TupleTableSlot *(*IterateDirectModify_function) (ForeignScanState *node)
 
 typedef void (*EndDirectModify_function) (ForeignScanState *node);
 
+typedef void (*ExecForeignTruncate_function) (Relation frel);
+
 typedef RowMarkType (*GetForeignRowMarkType_function) (RangeTblEntry *rte,
 													   LockClauseStrength strength);
 
@@ -220,6 +222,9 @@ typedef struct FdwRoutine
 	IterateDirectModify_function IterateDirectModify;
 	EndDirectModify_function EndDirectModify;
 
+	/* Functions for truncating foreign tables */
+	ExecForeignTruncate_function ExecForeignTruncate;
+
 	/* Functions for SELECT FOR UPDATE/SHARE row locking */
 	GetForeignRowMarkType_function GetForeignRowMarkType;
 	RefetchForeignRow_function RefetchForeignRow;

 contrib/postgres_fdw/deparse.c                 |   9 ++
 contrib/postgres_fdw/expected/postgres_fdw.out | 144 +++++++++++++++++++++++++
 contrib/postgres_fdw/postgres_fdw.c            |  57 ++++++++++
 contrib/postgres_fdw/postgres_fdw.h            |   1 +
 contrib/postgres_fdw/sql/postgres_fdw.sql      |  51 +++++++++
 doc/src/sgml/fdwhandler.sgml                   |  37 +++++++
 src/backend/commands/tablecmds.c               |  60 ++++++++++-
 src/include/foreign/fdwapi.h                   |   7 ++
 8 files changed, 362 insertions(+), 4 deletions(-)

diff --git a/contrib/postgres_fdw/deparse.c b/contrib/postgres_fdw/deparse.c
index a3639e9604..aaa38cb482 100644
--- a/contrib/postgres_fdw/deparse.c
+++ b/contrib/postgres_fdw/deparse.c
@@ -2098,6 +2098,15 @@ deparseAnalyzeSql(StringInfo buf, Relation rel, List **retrieved_attrs)
 	deparseRelation(buf, rel);
 }
 
+/*
+ * Construct a simple "TRUNCATE rel" statement
+ */
+void
+deparseTruncateSql(StringInfo buf, Relation rel)
+{
+	deparseRelation(buf, rel);
+}
+
 /*
  * Construct name to use for given column, and emit it into buf.
  * If it has a column_name FDW option, use that instead of attribute name.
diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 0912d6cd5e..0421f172f5 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8168,6 +8168,150 @@ select * from rem3;
 
 drop foreign table rem3;
 drop table loc3;
+-- ===================================================================
+-- test for TRUNCATE
+-- ===================================================================
+CREATE TABLE tru_nt (id int, x text);
+CREATE FOREIGN TABLE tru_ft (id int, x text)
+       SERVER loopback OPTIONS (table_name 'tru_nt');
+INSERT INTO tru_nt (SELECT x,md5(x::text) FROM generate_series(1,10) x);
+CREATE TABLE tru_pt (id int, y text) PARTITION BY HASH(id);
+CREATE TABLE tru_pt__p0 PARTITION OF tru_pt
+                        FOR VALUES WITH (MODULUS 2, REMAINDER 0);
+CREATE TABLE __tru_pt__p1 (id int, y text);
+CREATE FOREIGN TABLE tru_pt__p1 PARTITION OF tru_pt
+                                FOR VALUES WITH (MODULUS 2, REMAINDER 1)
+               SERVER loopback OPTIONS (table_name '__tru_pt__p1');
+INSERT INTO tru_pt (SELECT x,md5(x::text) FROM generate_series(11,30) x);
+CREATE TABLE tru_pk (id int primary key, x text);
+INSERT INTO tru_pk (SELECT x,md5((x+1)::text) FROM generate_series(1,10) x);
+CREATE TABLE tru_fk (fkey int references tru_pk(id));
+INSERT INTO tru_fk (SELECT x % 10 + 1 FROM generate_series(1,30) x);
+CREATE FOREIGN TABLE tru_ft_ref (id int, x text)
+       SERVER loopback OPTIONS (table_name 'tru_pk');
+-- normal truncate
+SELECT * FROM tru_ft;
+ id |                x                 
+----+----------------------------------
+  1 | c4ca4238a0b923820dcc509a6f75849b
+  2 | c81e728d9d4c2f636f067f89cc14862c
+  3 | eccbc87e4b5ce2fe28308fd9f2a7baf3
+  4 | a87ff679a2f3e71d9181a67b7542122c
+  5 | e4da3b7fbbce2345d7772b0674a318d5
+  6 | 1679091c5a880faf6fb5e6087eb1b2dc
+  7 | 8f14e45fceea167a5a36dedd4bea2543
+  8 | c9f0f895fb98ab9159f51fd0297e236d
+  9 | 45c48cce2e2d7fbdea1afc51c7c6ad26
+ 10 | d3d9446802a44259755d38e6d163e820
+(10 rows)
+
+TRUNCATE tru_ft;
+SELECT * FROM tru_nt;
+ id | x 
+----+---
+(0 rows)
+
+SELECT * FROM tru_ft;
+ id | x 
+----+---
+(0 rows)
+
+-- partition table mixtured by table and foreign table
+SELECT * FROM tru_pt;
+ id |                y                 
+----+----------------------------------
+ 12 | c20ad4d76fe97759aa27a0c99bff6710
+ 13 | c51ce410c124a10e0db5e4b97fc2af39
+ 14 | aab3238922bcc25a6f606eb525ffdc56
+ 16 | c74d97b01eae257e44aa9d5bade97baf
+ 17 | 70efdf2ec9b086079795c442636b55fb
+ 18 | 6f4922f45568161a8cdf4ad2299f6d23
+ 23 | 37693cfc748049e45d87b8c7d8b9aacd
+ 25 | 8e296a067a37563370ded05f5a3bf3ec
+ 26 | 4e732ced3463d06de0ca9a15b6153677
+ 27 | 02e74f10e0327ad868d138f2b4fdd6f0
+ 28 | 33e75ff09dd601bbe69f351039152189
+ 30 | 34173cb38f07f89ddbebc2ac9128303f
+ 11 | 6512bd43d9caa6e02c990b0a82652dca
+ 15 | 9bf31c7ff062936a96d3c8bd1f8f2ff3
+ 19 | 1f0e3dad99908345f7439f8ffabdffc4
+ 20 | 98f13708210194c475687be6106a3b84
+ 21 | 3c59dc048e8850243be8079a5c74d079
+ 22 | b6d767d2f8ed5d21a44b0e5886680cb9
+ 24 | 1ff1de774005f8da13f42943881c655f
+ 29 | 6ea9ab1baa0efb9e19094440c317e21b
+(20 rows)
+
+TRUNCATE tru_pt;
+SELECT * FROM tru_pt;
+ id | y 
+----+---
+(0 rows)
+
+SELECT * FROM tru_pt__p0;
+ id | y 
+----+---
+(0 rows)
+
+SELECT * FROM tru_pt__p1;
+ id | y 
+----+---
+(0 rows)
+
+SELECT * FROM __tru_pt__p1;
+ id | y 
+----+---
+(0 rows)
+
+-- 'CASCADE' option
+SELECT * FROM tru_ft_ref;
+ id |                x                 
+----+----------------------------------
+  1 | c81e728d9d4c2f636f067f89cc14862c
+  2 | eccbc87e4b5ce2fe28308fd9f2a7baf3
+  3 | a87ff679a2f3e71d9181a67b7542122c
+  4 | e4da3b7fbbce2345d7772b0674a318d5
+  5 | 1679091c5a880faf6fb5e6087eb1b2dc
+  6 | 8f14e45fceea167a5a36dedd4bea2543
+  7 | c9f0f895fb98ab9159f51fd0297e236d
+  8 | 45c48cce2e2d7fbdea1afc51c7c6ad26
+  9 | d3d9446802a44259755d38e6d163e820
+ 10 | 6512bd43d9caa6e02c990b0a82652dca
+(10 rows)
+
+TRUNCATE tru_ft_ref;	-- failed
+ERROR:  cannot truncate a table referenced in a foreign key constraint
+DETAIL:  Table "tru_fk" references "tru_pk".
+HINT:  Truncate table "tru_fk" at the same time, or use TRUNCATE ... CASCADE.
+CONTEXT:  remote SQL command: TRUNCATE public.tru_pk CONTINUE IDENTITY RESTRICT
+TRUNCATE tru_ft_ref CASCADE;
+SELECT * FROM tru_ft_ref;
+ id | x 
+----+---
+(0 rows)
+
+-- truncate two tables at a command
+INSERT INTO tru_ft (SELECT x,md5((x+2)::text) FROM generate_series(1,8) x);
+INSERT INTO tru_ft_ref (SELECT x,md5((x+3)::text) FROM generate_series(1,8) x);
+SELECT * FROM tru_ft a, tru_ft_ref b WHERE a.id = b.id;
+ id |                x                 | id |                x                 
+----+----------------------------------+----+----------------------------------
+  1 | eccbc87e4b5ce2fe28308fd9f2a7baf3 |  1 | a87ff679a2f3e71d9181a67b7542122c
+  2 | a87ff679a2f3e71d9181a67b7542122c |  2 | e4da3b7fbbce2345d7772b0674a318d5
+  3 | e4da3b7fbbce2345d7772b0674a318d5 |  3 | 1679091c5a880faf6fb5e6087eb1b2dc
+  4 | 1679091c5a880faf6fb5e6087eb1b2dc |  4 | 8f14e45fceea167a5a36dedd4bea2543
+  5 | 8f14e45fceea167a5a36dedd4bea2543 |  5 | c9f0f895fb98ab9159f51fd0297e236d
+  6 | c9f0f895fb98ab9159f51fd0297e236d |  6 | 45c48cce2e2d7fbdea1afc51c7c6ad26
+  7 | 45c48cce2e2d7fbdea1afc51c7c6ad26 |  7 | d3d9446802a44259755d38e6d163e820
+  8 | d3d9446802a44259755d38e6d163e820 |  8 | 6512bd43d9caa6e02c990b0a82652dca
+(8 rows)
+
+TRUNCATE tru_ft, tru_ft_ref CASCADE;
+SELECT * FROM tru_ft a, tru_ft_ref b WHERE a.id = b.id;
+ id | x | id | x 
+----+---+----+---
+(0 rows)
+
 -- ===================================================================
 -- test IMPORT FOREIGN SCHEMA
 -- ===================================================================
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index 2175dff824..0cbbb58e89 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -373,6 +373,9 @@ static void postgresExplainForeignModify(ModifyTableState *mtstate,
 										 ExplainState *es);
 static void postgresExplainDirectModify(ForeignScanState *node,
 										ExplainState *es);
+static void postgresExecForeignTruncate(List *frels_list,
+										bool is_cascade,
+										bool restart_seqs);
 static bool postgresAnalyzeForeignTable(Relation relation,
 										AcquireSampleRowsFunc *func,
 										BlockNumber *totalpages);
@@ -546,6 +549,9 @@ postgres_fdw_handler(PG_FUNCTION_ARGS)
 	routine->ExplainForeignModify = postgresExplainForeignModify;
 	routine->ExplainDirectModify = postgresExplainDirectModify;
 
+	/* Support function for TRUNCATE */
+	routine->ExecForeignTruncate = postgresExecForeignTruncate;
+
 	/* Support functions for ANALYZE */
 	routine->AnalyzeForeignTable = postgresAnalyzeForeignTable;
 
@@ -2656,6 +2662,57 @@ postgresExplainDirectModify(ForeignScanState *node, ExplainState *es)
 	}
 }
 
+/*
+ * postgresExecForeignTruncate
+ *		It propagates TRUNCATE command to the remote host inside of the
+ *		transaction block.
+ */
+static void
+postgresExecForeignTruncate(List *frels_list,
+							bool is_cascade,
+							bool restart_seqs)
+{
+	Oid				server_id = InvalidOid;
+	UserMapping	   *user = NULL;
+	PGconn		   *conn = NULL;
+	PGresult	   *res;
+	StringInfoData	sql;
+	ListCell	   *lc;
+
+	/* set up remote query */
+	initStringInfo(&sql);
+	appendStringInfoString(&sql, "TRUNCATE ");
+	foreach (lc, frels_list)
+	{
+		Relation	frel = lfirst(lc);
+		Oid			frel_oid = RelationGetRelid(frel);
+
+		if (!OidIsValid(server_id))
+		{
+			server_id = GetForeignServerIdByRelId(frel_oid);
+			user = GetUserMapping(GetUserId(), server_id);
+			conn = GetConnection(user, false);
+		}
+		else
+		{
+			Assert(server_id == GetForeignServerIdByRelId(frel_oid));
+			appendStringInfoString(&sql, ", ");
+		}
+		deparseTruncateSql(&sql, frel);
+	}
+	appendStringInfo(&sql, " %s IDENTITY %s",
+					 restart_seqs ? "RESTART" : "CONTINUE",
+					 is_cascade ? "CASCADE" : "RESTRICT");
+
+	if (!PQsendQuery(conn, sql.data))
+		pgfdw_report_error(ERROR, NULL, conn, false, sql.data);
+	res = pgfdw_get_result(conn, sql.data);
+	if (PQresultStatus(res) != PGRES_COMMAND_OK)
+		pgfdw_report_error(ERROR, res, conn, true, sql.data);
+	/* clean-up */
+	PQclear(res);
+	pfree(sql.data);
+}
 
 /*
  * estimate_path_cost_size
diff --git a/contrib/postgres_fdw/postgres_fdw.h b/contrib/postgres_fdw/postgres_fdw.h
index eef410db39..ab2eefb126 100644
--- a/contrib/postgres_fdw/postgres_fdw.h
+++ b/contrib/postgres_fdw/postgres_fdw.h
@@ -190,6 +190,7 @@ extern void deparseDirectDeleteSql(StringInfo buf, PlannerInfo *root,
 extern void deparseAnalyzeSizeSql(StringInfo buf, Relation rel);
 extern void deparseAnalyzeSql(StringInfo buf, Relation rel,
 							  List **retrieved_attrs);
+extern void deparseTruncateSql(StringInfo buf, Relation rel);
 extern void deparseStringLiteral(StringInfo buf, const char *val);
 extern Expr *find_em_expr_for_rel(EquivalenceClass *ec, RelOptInfo *rel);
 extern Expr *find_em_expr_for_input_target(PlannerInfo *root,
diff --git a/contrib/postgres_fdw/sql/postgres_fdw.sql b/contrib/postgres_fdw/sql/postgres_fdw.sql
index f2a4089e9d..44857bf5a4 100644
--- a/contrib/postgres_fdw/sql/postgres_fdw.sql
+++ b/contrib/postgres_fdw/sql/postgres_fdw.sql
@@ -2287,6 +2287,57 @@ select * from rem3;
 drop foreign table rem3;
 drop table loc3;
 
+-- ===================================================================
+-- test for TRUNCATE
+-- ===================================================================
+CREATE TABLE tru_nt (id int, x text);
+CREATE FOREIGN TABLE tru_ft (id int, x text)
+       SERVER loopback OPTIONS (table_name 'tru_nt');
+INSERT INTO tru_nt (SELECT x,md5(x::text) FROM generate_series(1,10) x);
+
+CREATE TABLE tru_pt (id int, y text) PARTITION BY HASH(id);
+CREATE TABLE tru_pt__p0 PARTITION OF tru_pt
+                        FOR VALUES WITH (MODULUS 2, REMAINDER 0);
+CREATE TABLE __tru_pt__p1 (id int, y text);
+CREATE FOREIGN TABLE tru_pt__p1 PARTITION OF tru_pt
+                                FOR VALUES WITH (MODULUS 2, REMAINDER 1)
+               SERVER loopback OPTIONS (table_name '__tru_pt__p1');
+INSERT INTO tru_pt (SELECT x,md5(x::text) FROM generate_series(11,30) x);
+
+CREATE TABLE tru_pk (id int primary key, x text);
+INSERT INTO tru_pk (SELECT x,md5((x+1)::text) FROM generate_series(1,10) x);
+CREATE TABLE tru_fk (fkey int references tru_pk(id));
+INSERT INTO tru_fk (SELECT x % 10 + 1 FROM generate_series(1,30) x);
+CREATE FOREIGN TABLE tru_ft_ref (id int, x text)
+       SERVER loopback OPTIONS (table_name 'tru_pk');
+
+-- normal truncate
+SELECT * FROM tru_ft;
+TRUNCATE tru_ft;
+SELECT * FROM tru_nt;
+SELECT * FROM tru_ft;
+
+-- partition table mixtured by table and foreign table
+SELECT * FROM tru_pt;
+TRUNCATE tru_pt;
+SELECT * FROM tru_pt;
+SELECT * FROM tru_pt__p0;
+SELECT * FROM tru_pt__p1;
+SELECT * FROM __tru_pt__p1;
+
+-- 'CASCADE' option
+SELECT * FROM tru_ft_ref;
+TRUNCATE tru_ft_ref;	-- failed
+TRUNCATE tru_ft_ref CASCADE;
+SELECT * FROM tru_ft_ref;
+
+-- truncate two tables at a command
+INSERT INTO tru_ft (SELECT x,md5((x+2)::text) FROM generate_series(1,8) x);
+INSERT INTO tru_ft_ref (SELECT x,md5((x+3)::text) FROM generate_series(1,8) x);
+SELECT * FROM tru_ft a, tru_ft_ref b WHERE a.id = b.id;
+TRUNCATE tru_ft, tru_ft_ref CASCADE;
+SELECT * FROM tru_ft a, tru_ft_ref b WHERE a.id = b.id;
+
 -- ===================================================================
 -- test IMPORT FOREIGN SCHEMA
 -- ===================================================================
diff --git a/doc/src/sgml/fdwhandler.sgml b/doc/src/sgml/fdwhandler.sgml
index 6587678af2..0c16f90d8d 100644
--- a/doc/src/sgml/fdwhandler.sgml
+++ b/doc/src/sgml/fdwhandler.sgml
@@ -968,6 +968,43 @@ EndDirectModify(ForeignScanState *node);
 
    </sect2>
 
+   <sect2 id="fdw-callbacks-truncate">
+    <title>FDW Routines for Truncate</title>
+<programlisting>
+void
+ExecForeignTruncate(List *frels_list, bool is_cascade, bool restart_seqs);
+</programlisting>
+    <para>
+     Executes remote truncate on the remote relation associated with this
+     foreign table. This optional function is called during execution of
+     <command>TRUNCATE</command>, for each foreign server being involved.
+     (Note that invocations are not per foreign table.)
+
+     If FDW does not provide this callback, PostgreSQL considers
+     <command>TRUNCATE</command> is not supported on the foreign table.
+    </para>
+    <para>
+     <literal>frels_list</literal> is a list of foreign tables that are
+     connected to a particular foreign server; thus, these foreign tables
+     should have identical foreign server ID.
+
+     <literal>is_cascade</literal> tells us whether <literal>CASCADE</literal>
+     option is supplied, and <literal>restart_seqs</literal> also tells us
+     whether <literal>RESTART IDENTITY</literal> option is supplied at the
+     <command>TRUNCATE</command> command.
+    </para>
+    <para>
+     Pay attention that <command>TRUNCATE</command> can be transaction-safe
+     in <productname>PostgreSQL</productname>.
+     We can revert the <command>TRUNCATE</command> operation unless current
+     transaction is not committed, however, it is not true on some other
+     database products.
+     If FDW author considers to support <command>TRUNCATE</command> on their
+     FDW driver, it may not be sufficient just to run a
+     <command>TRUNCATE</command> command on the remote side.
+    </para>
+   </sect2>
+
    <sect2 id="fdw-callbacks-row-locking">
     <title>FDW Routines for Row Locking</title>
 
diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index 421bc28727..2f80451060 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -60,6 +60,7 @@
 #include "commands/user.h"
 #include "executor/executor.h"
 #include "foreign/foreign.h"
+#include "foreign/fdwapi.h"
 #include "miscadmin.h"
 #include "nodes/makefuncs.h"
 #include "nodes/nodeFuncs.h"
@@ -1624,6 +1625,8 @@ ExecuteTruncateGuts(List *explicit_rels, List *relids, List *relids_logged,
 {
 	List	   *rels;
 	List	   *seq_relids = NIL;
+	List	   *servs_list = NIL;
+	List	   *frels_list = NIL;
 	EState	   *estate;
 	ResultRelInfo *resultRelInfos;
 	ResultRelInfo *resultRelInfo;
@@ -1768,6 +1771,16 @@ ExecuteTruncateGuts(List *explicit_rels, List *relids, List *relids_logged,
 		/* Skip partitioned tables as there is nothing to do */
 		if (rel->rd_rel->relkind == RELKIND_PARTITIONED_TABLE)
 			continue;
+		/* Remember the server and foreign-tables to be truncated */
+		if (rel->rd_rel->relkind == RELKIND_FOREIGN_TABLE)
+		{
+			Oid		frel_oid = RelationGetRelid(rel);
+			Oid		server_id = GetForeignServerIdByRelId(frel_oid);
+
+			servs_list = list_append_unique_oid(servs_list, server_id);
+			frels_list = lappend(frels_list, rel);
+			continue;
+		}
 
 		/*
 		 * Normally, we need a transaction-safe truncation here.  However, if
@@ -1829,6 +1842,34 @@ ExecuteTruncateGuts(List *explicit_rels, List *relids, List *relids_logged,
 		pgstat_count_truncate(rel);
 	}
 
+	/*
+	 * Invocation of FDW handler for each foreign server
+	 */
+	foreach (cell, servs_list)
+	{
+		Oid			server_id = lfirst_oid(cell);
+		FdwRoutine *routine = GetFdwRoutineByServerId(server_id);
+		List	   *curr_frels = NIL;
+		ListCell   *lc;
+
+		foreach (lc, frels_list)
+		{
+			Relation	frel = lfirst(lc);
+			Oid			frel_oid = RelationGetRelid(frel);
+
+			if (server_id == GetForeignServerIdByRelId(frel_oid))
+			{
+				frels_list = foreach_delete_current(frels_list, lc);
+				curr_frels = lappend(curr_frels, frel);
+			}
+		}
+		Assert(curr_frels != NIL);
+		Assert(routine->ExecForeignTruncate != NULL);
+		routine->ExecForeignTruncate(curr_frels,
+									 behavior == DROP_CASCADE,
+									 restart_seqs);
+	}
+
 	/*
 	 * Restart owned sequences if we were asked to.
 	 */
@@ -1916,12 +1957,23 @@ truncate_check_rel(Oid relid, Form_pg_class reltuple)
 	char	   *relname = NameStr(reltuple->relname);
 
 	/*
-	 * Only allow truncate on regular tables and partitioned tables (although,
+	 * Only allow truncate on regular tables, partitioned tables (although,
 	 * the latter are only being included here for the following checks; no
-	 * physical truncation will occur in their case.)
+	 * physical truncation will occur in their case.) and foreign tables
+	 * that support ExecForeignTruncate callback.
 	 */
-	if (reltuple->relkind != RELKIND_RELATION &&
-		reltuple->relkind != RELKIND_PARTITIONED_TABLE)
+	if (reltuple->relkind == RELKIND_FOREIGN_TABLE)
+	{
+		FdwRoutine *fdwroutine = GetFdwRoutineByRelId(relid);
+
+		if (!fdwroutine->ExecForeignTruncate)
+			ereport(ERROR,
+					(errcode(ERRCODE_WRONG_OBJECT_TYPE),
+					 errmsg("\"%s\" is not a supported foreign table",
+							relname)));
+	}
+	else if (reltuple->relkind != RELKIND_RELATION &&
+			 reltuple->relkind != RELKIND_PARTITIONED_TABLE)
 		ereport(ERROR,
 				(errcode(ERRCODE_WRONG_OBJECT_TYPE),
 				 errmsg("\"%s\" is not a table", relname)));
diff --git a/src/include/foreign/fdwapi.h b/src/include/foreign/fdwapi.h
index 95556dfb15..c8864f2052 100644
--- a/src/include/foreign/fdwapi.h
+++ b/src/include/foreign/fdwapi.h
@@ -118,6 +118,10 @@ typedef TupleTableSlot *(*IterateDirectModify_function) (ForeignScanState *node)
 
 typedef void (*EndDirectModify_function) (ForeignScanState *node);
 
+typedef void (*ExecForeignTruncate_function) (List *frels_list,
+											  bool is_cascade,
+											  bool restart_seqs);
+
 typedef RowMarkType (*GetForeignRowMarkType_function) (RangeTblEntry *rte,
 													   LockClauseStrength strength);
 
@@ -220,6 +224,9 @@ typedef struct FdwRoutine
 	IterateDirectModify_function IterateDirectModify;
 	EndDirectModify_function EndDirectModify;
 
+	/* Functions for truncating foreign tables */
+	ExecForeignTruncate_function ExecForeignTruncate;
+
 	/* Functions for SELECT FOR UPDATE/SHARE row locking */
 	GetForeignRowMarkType_function GetForeignRowMarkType;
 	RefetchForeignRow_function RefetchForeignRow;

 contrib/postgres_fdw/deparse.c                 |  34 ++++++
 contrib/postgres_fdw/expected/postgres_fdw.out | 144 +++++++++++++++++++++++++
 contrib/postgres_fdw/postgres_fdw.c            |  51 +++++++++
 contrib/postgres_fdw/postgres_fdw.h            |   2 +
 contrib/postgres_fdw/sql/postgres_fdw.sql      |  51 +++++++++
 doc/src/sgml/fdwhandler.sgml                   |  39 +++++++
 src/backend/commands/tablecmds.c               |  90 +++++++++++++++-
 src/include/foreign/fdwapi.h                   |   7 ++
 src/test/regress/expected/foreign_data.out     |   8 +-
 9 files changed, 418 insertions(+), 8 deletions(-)

diff --git a/contrib/postgres_fdw/deparse.c b/contrib/postgres_fdw/deparse.c
index a3639e9604..05e95144f9 100644
--- a/contrib/postgres_fdw/deparse.c
+++ b/contrib/postgres_fdw/deparse.c
@@ -2098,6 +2098,40 @@ deparseAnalyzeSql(StringInfo buf, Relation rel, List **retrieved_attrs)
 	deparseRelation(buf, rel);
 }
 
+/*
+ * Construct a simple "TRUNCATE rel" statement
+ */
+void
+deparseTruncateSql(StringInfo buf, List *frels_list,
+				   DropBehavior behavior, bool restart_seqs)
+{
+	ListCell   *lc;
+
+	appendStringInfoString(buf, "TRUNCATE ");
+	foreach (lc, frels_list)
+	{
+		Relation	frel = lfirst(lc);
+
+		if (lc != list_head(frels_list))
+			appendStringInfoString(buf, ", ");
+		deparseRelation(buf, frel);
+	}
+	appendStringInfo(buf, " %s IDENTITY",
+					 restart_seqs ? "RESTART" : "CONTINUE");
+	switch (behavior)
+	{
+		case DROP_RESTRICT:
+			appendStringInfoString(buf, " RESTRICT");
+			break;
+		case DROP_CASCADE:
+			appendStringInfoString(buf, " CASCADE");
+			break;
+		default:
+			elog(ERROR, "Bug? unexpected DropBehavior (%d)", (int)behavior);
+			break;
+	}
+}
+
 /*
  * Construct name to use for given column, and emit it into buf.
  * If it has a column_name FDW option, use that instead of attribute name.
diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 84fd3ad2e0..ef10c8f709 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8168,6 +8168,150 @@ select * from rem3;
 
 drop foreign table rem3;
 drop table loc3;
+-- ===================================================================
+-- test for TRUNCATE
+-- ===================================================================
+CREATE TABLE tru_nt (id int, x text);
+CREATE FOREIGN TABLE tru_ft (id int, x text)
+       SERVER loopback OPTIONS (table_name 'tru_nt');
+INSERT INTO tru_nt (SELECT x,md5(x::text) FROM generate_series(1,10) x);
+CREATE TABLE tru_pt (id int, y text) PARTITION BY HASH(id);
+CREATE TABLE tru_pt__p0 PARTITION OF tru_pt
+                        FOR VALUES WITH (MODULUS 2, REMAINDER 0);
+CREATE TABLE __tru_pt__p1 (id int, y text);
+CREATE FOREIGN TABLE tru_pt__p1 PARTITION OF tru_pt
+                                FOR VALUES WITH (MODULUS 2, REMAINDER 1)
+               SERVER loopback OPTIONS (table_name '__tru_pt__p1');
+INSERT INTO tru_pt (SELECT x,md5(x::text) FROM generate_series(11,30) x);
+CREATE TABLE tru_pk (id int primary key, x text);
+INSERT INTO tru_pk (SELECT x,md5((x+1)::text) FROM generate_series(1,10) x);
+CREATE TABLE tru_fk (fkey int references tru_pk(id));
+INSERT INTO tru_fk (SELECT x % 10 + 1 FROM generate_series(1,30) x);
+CREATE FOREIGN TABLE tru_ft_ref (id int, x text)
+       SERVER loopback OPTIONS (table_name 'tru_pk');
+-- normal truncate
+SELECT * FROM tru_ft;
+ id |                x                 
+----+----------------------------------
+  1 | c4ca4238a0b923820dcc509a6f75849b
+  2 | c81e728d9d4c2f636f067f89cc14862c
+  3 | eccbc87e4b5ce2fe28308fd9f2a7baf3
+  4 | a87ff679a2f3e71d9181a67b7542122c
+  5 | e4da3b7fbbce2345d7772b0674a318d5
+  6 | 1679091c5a880faf6fb5e6087eb1b2dc
+  7 | 8f14e45fceea167a5a36dedd4bea2543
+  8 | c9f0f895fb98ab9159f51fd0297e236d
+  9 | 45c48cce2e2d7fbdea1afc51c7c6ad26
+ 10 | d3d9446802a44259755d38e6d163e820
+(10 rows)
+
+TRUNCATE tru_ft;
+SELECT * FROM tru_nt;
+ id | x 
+----+---
+(0 rows)
+
+SELECT * FROM tru_ft;
+ id | x 
+----+---
+(0 rows)
+
+-- partition table mixtured by table and foreign table
+SELECT * FROM tru_pt;
+ id |                y                 
+----+----------------------------------
+ 12 | c20ad4d76fe97759aa27a0c99bff6710
+ 13 | c51ce410c124a10e0db5e4b97fc2af39
+ 14 | aab3238922bcc25a6f606eb525ffdc56
+ 16 | c74d97b01eae257e44aa9d5bade97baf
+ 17 | 70efdf2ec9b086079795c442636b55fb
+ 18 | 6f4922f45568161a8cdf4ad2299f6d23
+ 23 | 37693cfc748049e45d87b8c7d8b9aacd
+ 25 | 8e296a067a37563370ded05f5a3bf3ec
+ 26 | 4e732ced3463d06de0ca9a15b6153677
+ 27 | 02e74f10e0327ad868d138f2b4fdd6f0
+ 28 | 33e75ff09dd601bbe69f351039152189
+ 30 | 34173cb38f07f89ddbebc2ac9128303f
+ 11 | 6512bd43d9caa6e02c990b0a82652dca
+ 15 | 9bf31c7ff062936a96d3c8bd1f8f2ff3
+ 19 | 1f0e3dad99908345f7439f8ffabdffc4
+ 20 | 98f13708210194c475687be6106a3b84
+ 21 | 3c59dc048e8850243be8079a5c74d079
+ 22 | b6d767d2f8ed5d21a44b0e5886680cb9
+ 24 | 1ff1de774005f8da13f42943881c655f
+ 29 | 6ea9ab1baa0efb9e19094440c317e21b
+(20 rows)
+
+TRUNCATE tru_pt;
+SELECT * FROM tru_pt;
+ id | y 
+----+---
+(0 rows)
+
+SELECT * FROM tru_pt__p0;
+ id | y 
+----+---
+(0 rows)
+
+SELECT * FROM tru_pt__p1;
+ id | y 
+----+---
+(0 rows)
+
+SELECT * FROM __tru_pt__p1;
+ id | y 
+----+---
+(0 rows)
+
+-- 'CASCADE' option
+SELECT * FROM tru_ft_ref;
+ id |                x                 
+----+----------------------------------
+  1 | c81e728d9d4c2f636f067f89cc14862c
+  2 | eccbc87e4b5ce2fe28308fd9f2a7baf3
+  3 | a87ff679a2f3e71d9181a67b7542122c
+  4 | e4da3b7fbbce2345d7772b0674a318d5
+  5 | 1679091c5a880faf6fb5e6087eb1b2dc
+  6 | 8f14e45fceea167a5a36dedd4bea2543
+  7 | c9f0f895fb98ab9159f51fd0297e236d
+  8 | 45c48cce2e2d7fbdea1afc51c7c6ad26
+  9 | d3d9446802a44259755d38e6d163e820
+ 10 | 6512bd43d9caa6e02c990b0a82652dca
+(10 rows)
+
+TRUNCATE tru_ft_ref;	-- failed
+ERROR:  cannot truncate a table referenced in a foreign key constraint
+DETAIL:  Table "tru_fk" references "tru_pk".
+HINT:  Truncate table "tru_fk" at the same time, or use TRUNCATE ... CASCADE.
+CONTEXT:  remote SQL command: TRUNCATE public.tru_pk CONTINUE IDENTITY RESTRICT
+TRUNCATE tru_ft_ref CASCADE;
+SELECT * FROM tru_ft_ref;
+ id | x 
+----+---
+(0 rows)
+
+-- truncate two tables at a command
+INSERT INTO tru_ft (SELECT x,md5((x+2)::text) FROM generate_series(1,8) x);
+INSERT INTO tru_ft_ref (SELECT x,md5((x+3)::text) FROM generate_series(1,8) x);
+SELECT * FROM tru_ft a, tru_ft_ref b WHERE a.id = b.id;
+ id |                x                 | id |                x                 
+----+----------------------------------+----+----------------------------------
+  1 | eccbc87e4b5ce2fe28308fd9f2a7baf3 |  1 | a87ff679a2f3e71d9181a67b7542122c
+  2 | a87ff679a2f3e71d9181a67b7542122c |  2 | e4da3b7fbbce2345d7772b0674a318d5
+  3 | e4da3b7fbbce2345d7772b0674a318d5 |  3 | 1679091c5a880faf6fb5e6087eb1b2dc
+  4 | 1679091c5a880faf6fb5e6087eb1b2dc |  4 | 8f14e45fceea167a5a36dedd4bea2543
+  5 | 8f14e45fceea167a5a36dedd4bea2543 |  5 | c9f0f895fb98ab9159f51fd0297e236d
+  6 | c9f0f895fb98ab9159f51fd0297e236d |  6 | 45c48cce2e2d7fbdea1afc51c7c6ad26
+  7 | 45c48cce2e2d7fbdea1afc51c7c6ad26 |  7 | d3d9446802a44259755d38e6d163e820
+  8 | d3d9446802a44259755d38e6d163e820 |  8 | 6512bd43d9caa6e02c990b0a82652dca
+(8 rows)
+
+TRUNCATE tru_ft, tru_ft_ref CASCADE;
+SELECT * FROM tru_ft a, tru_ft_ref b WHERE a.id = b.id;
+ id | x | id | x 
+----+---+----+---
+(0 rows)
+
 -- ===================================================================
 -- test IMPORT FOREIGN SCHEMA
 -- ===================================================================
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index 2175dff824..ded54ab5e9 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -373,6 +373,9 @@ static void postgresExplainForeignModify(ModifyTableState *mtstate,
 										 ExplainState *es);
 static void postgresExplainDirectModify(ForeignScanState *node,
 										ExplainState *es);
+static void postgresExecForeignTruncate(List *frels_list,
+										DropBehavior behavior,
+										bool restart_seqs);
 static bool postgresAnalyzeForeignTable(Relation relation,
 										AcquireSampleRowsFunc *func,
 										BlockNumber *totalpages);
@@ -546,6 +549,9 @@ postgres_fdw_handler(PG_FUNCTION_ARGS)
 	routine->ExplainForeignModify = postgresExplainForeignModify;
 	routine->ExplainDirectModify = postgresExplainDirectModify;
 
+	/* Support function for TRUNCATE */
+	routine->ExecForeignTruncate = postgresExecForeignTruncate;
+
 	/* Support functions for ANALYZE */
 	routine->AnalyzeForeignTable = postgresAnalyzeForeignTable;
 
@@ -2656,6 +2662,51 @@ postgresExplainDirectModify(ForeignScanState *node, ExplainState *es)
 	}
 }
 
+/*
+ * postgresExecForeignTruncate
+ *		It propagates TRUNCATE command to the remote host inside of the
+ *		transaction block.
+ */
+static void
+postgresExecForeignTruncate(List *frels_list,
+							DropBehavior behavior,
+							bool restart_seqs)
+{
+	Oid				server_id = InvalidOid;
+	UserMapping	   *user = NULL;
+	PGconn		   *conn = NULL;
+	PGresult	   *res;
+	StringInfoData	sql;
+	ListCell	   *lc;
+
+	/* pick up remote connection, and sanity checks */
+	foreach (lc, frels_list)
+	{
+		Relation	frel = lfirst(lc);
+		Oid			frel_oid = RelationGetRelid(frel);
+
+		if (!OidIsValid(server_id))
+		{
+			server_id = GetForeignServerIdByRelId(frel_oid);
+			user = GetUserMapping(GetUserId(), server_id);
+			conn = GetConnection(user, false);
+		}
+		else if (server_id != GetForeignServerIdByRelId(frel_oid))
+			elog(ERROR, "Bug? inconsistent Server-IDs were supplied");
+	}
+	/* set up remote query */
+	initStringInfo(&sql);
+	deparseTruncateSql(&sql, frels_list, behavior, restart_seqs);
+	/* run remote query */
+	if (!PQsendQuery(conn, sql.data))
+		pgfdw_report_error(ERROR, NULL, conn, false, sql.data);
+	res = pgfdw_get_result(conn, sql.data);
+	if (PQresultStatus(res) != PGRES_COMMAND_OK)
+		pgfdw_report_error(ERROR, res, conn, true, sql.data);
+	/* clean-up */
+	PQclear(res);
+	pfree(sql.data);
+}
 
 /*
  * estimate_path_cost_size
diff --git a/contrib/postgres_fdw/postgres_fdw.h b/contrib/postgres_fdw/postgres_fdw.h
index eef410db39..1d75bf363a 100644
--- a/contrib/postgres_fdw/postgres_fdw.h
+++ b/contrib/postgres_fdw/postgres_fdw.h
@@ -190,6 +190,8 @@ extern void deparseDirectDeleteSql(StringInfo buf, PlannerInfo *root,
 extern void deparseAnalyzeSizeSql(StringInfo buf, Relation rel);
 extern void deparseAnalyzeSql(StringInfo buf, Relation rel,
 							  List **retrieved_attrs);
+extern void deparseTruncateSql(StringInfo buf, List *frels_list,
+							   DropBehavior behavior, bool restart_seqs);
 extern void deparseStringLiteral(StringInfo buf, const char *val);
 extern Expr *find_em_expr_for_rel(EquivalenceClass *ec, RelOptInfo *rel);
 extern Expr *find_em_expr_for_input_target(PlannerInfo *root,
diff --git a/contrib/postgres_fdw/sql/postgres_fdw.sql b/contrib/postgres_fdw/sql/postgres_fdw.sql
index acd7275c72..95c6e45975 100644
--- a/contrib/postgres_fdw/sql/postgres_fdw.sql
+++ b/contrib/postgres_fdw/sql/postgres_fdw.sql
@@ -2287,6 +2287,57 @@ select * from rem3;
 drop foreign table rem3;
 drop table loc3;
 
+-- ===================================================================
+-- test for TRUNCATE
+-- ===================================================================
+CREATE TABLE tru_nt (id int, x text);
+CREATE FOREIGN TABLE tru_ft (id int, x text)
+       SERVER loopback OPTIONS (table_name 'tru_nt');
+INSERT INTO tru_nt (SELECT x,md5(x::text) FROM generate_series(1,10) x);
+
+CREATE TABLE tru_pt (id int, y text) PARTITION BY HASH(id);
+CREATE TABLE tru_pt__p0 PARTITION OF tru_pt
+                        FOR VALUES WITH (MODULUS 2, REMAINDER 0);
+CREATE TABLE __tru_pt__p1 (id int, y text);
+CREATE FOREIGN TABLE tru_pt__p1 PARTITION OF tru_pt
+                                FOR VALUES WITH (MODULUS 2, REMAINDER 1)
+               SERVER loopback OPTIONS (table_name '__tru_pt__p1');
+INSERT INTO tru_pt (SELECT x,md5(x::text) FROM generate_series(11,30) x);
+
+CREATE TABLE tru_pk (id int primary key, x text);
+INSERT INTO tru_pk (SELECT x,md5((x+1)::text) FROM generate_series(1,10) x);
+CREATE TABLE tru_fk (fkey int references tru_pk(id));
+INSERT INTO tru_fk (SELECT x % 10 + 1 FROM generate_series(1,30) x);
+CREATE FOREIGN TABLE tru_ft_ref (id int, x text)
+       SERVER loopback OPTIONS (table_name 'tru_pk');
+
+-- normal truncate
+SELECT * FROM tru_ft;
+TRUNCATE tru_ft;
+SELECT * FROM tru_nt;
+SELECT * FROM tru_ft;
+
+-- partition table mixtured by table and foreign table
+SELECT * FROM tru_pt;
+TRUNCATE tru_pt;
+SELECT * FROM tru_pt;
+SELECT * FROM tru_pt__p0;
+SELECT * FROM tru_pt__p1;
+SELECT * FROM __tru_pt__p1;
+
+-- 'CASCADE' option
+SELECT * FROM tru_ft_ref;
+TRUNCATE tru_ft_ref;	-- failed
+TRUNCATE tru_ft_ref CASCADE;
+SELECT * FROM tru_ft_ref;
+
+-- truncate two tables at a command
+INSERT INTO tru_ft (SELECT x,md5((x+2)::text) FROM generate_series(1,8) x);
+INSERT INTO tru_ft_ref (SELECT x,md5((x+3)::text) FROM generate_series(1,8) x);
+SELECT * FROM tru_ft a, tru_ft_ref b WHERE a.id = b.id;
+TRUNCATE tru_ft, tru_ft_ref CASCADE;
+SELECT * FROM tru_ft a, tru_ft_ref b WHERE a.id = b.id;
+
 -- ===================================================================
 -- test IMPORT FOREIGN SCHEMA
 -- ===================================================================
diff --git a/doc/src/sgml/fdwhandler.sgml b/doc/src/sgml/fdwhandler.sgml
index 6587678af2..8a75d06047 100644
--- a/doc/src/sgml/fdwhandler.sgml
+++ b/doc/src/sgml/fdwhandler.sgml
@@ -968,6 +968,45 @@ EndDirectModify(ForeignScanState *node);
 
    </sect2>
 
+   <sect2 id="fdw-callbacks-truncate">
+    <title>FDW Routines for Truncate</title>
+<programlisting>
+void
+ExecForeignTruncate(List *frels_list,
+                    DropBehavior behavior, bool restart_seqs);
+</programlisting>
+    <para>
+     Executes remote truncate on the remote relation associated with this
+     foreign table. This optional function is called during execution of
+     <command>TRUNCATE</command>, for each foreign server being involved.
+     (Note that invocations are not per foreign table.)
+
+     If FDW does not provide this callback, PostgreSQL performs as if
+     <command>TRUNCATE</command> is not supported on the foreign table.
+    </para>
+    <para>
+     <literal>frels_list</literal> is a list of foreign tables that are
+     connected to a particular foreign server; thus, these foreign tables
+     should have identical foreign server ID.
+
+     <literal>behavior</literal> tells the FDW driver which options does
+     <command>TRUNCATE</command> command took; <literal>CASCADE</literal>
+     or <literal>RESTRICT</literal>.
+     <literal>restart_seqs</literal> also tells the FDW driver whether
+     <literal>RESTART IDENTITY</literal> option was supplied, or not.
+    </para>
+    <para>
+     Pay attention that <command>TRUNCATE</command> can be transaction-safe
+     in <productname>PostgreSQL</productname>.
+     We can revert the <command>TRUNCATE</command> operation unless current
+     transaction is not committed, however, it is not true on some other
+     database products.
+     If FDW author considers to support <command>TRUNCATE</command> on their
+     FDW driver, it may not be sufficient just to run a
+     <command>TRUNCATE</command> command on the remote side.
+    </para>
+   </sect2>
+
    <sect2 id="fdw-callbacks-row-locking">
     <title>FDW Routines for Row Locking</title>
 
diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index 30b72b6297..70a2e2d1bc 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -60,6 +60,7 @@
 #include "commands/user.h"
 #include "executor/executor.h"
 #include "foreign/foreign.h"
+#include "foreign/fdwapi.h"
 #include "miscadmin.h"
 #include "nodes/makefuncs.h"
 #include "nodes/nodeFuncs.h"
@@ -1628,6 +1629,16 @@ ExecuteTruncate(TruncateStmt *stmt)
 	}
 }
 
+/*
+ * ForeignTruncateInfo
+ */
+typedef struct
+{
+	Oid		server_id;
+	FdwRoutine *routine;
+	List   *frels_list;
+} ForeignTruncateInfo;
+
 /*
  * ExecuteTruncateGuts
  *
@@ -1647,6 +1658,7 @@ ExecuteTruncateGuts(List *explicit_rels, List *relids, List *relids_logged,
 {
 	List	   *rels;
 	List	   *seq_relids = NIL;
+	HTAB	   *ft_htab = NULL;
 	EState	   *estate;
 	ResultRelInfo *resultRelInfos;
 	ResultRelInfo *resultRelInfo;
@@ -1791,6 +1803,40 @@ ExecuteTruncateGuts(List *explicit_rels, List *relids, List *relids_logged,
 		/* Skip partitioned tables as there is nothing to do */
 		if (rel->rd_rel->relkind == RELKIND_PARTITIONED_TABLE)
 			continue;
+		/* Remember the server and foreign-tables to be truncated */
+		if (rel->rd_rel->relkind == RELKIND_FOREIGN_TABLE)
+		{
+			Oid		frel_oid = RelationGetRelid(rel);
+			Oid		server_id = GetForeignServerIdByRelId(frel_oid);
+			bool	found;
+			ForeignTruncateInfo *ft_info;
+
+			if (!ft_htab)
+			{
+				HASHCTL		hctl;
+
+				memset(&hctl, 0, sizeof(HASHCTL));
+				hctl.keysize = sizeof(Oid);
+				hctl.entrysize = sizeof(ForeignTruncateInfo);
+				/* temporary usage, to be released soon */
+				hctl.hcxt = CurrentMemoryContext;
+				ft_htab = hash_create("TRUNCATE Foreign Tables",
+									  128,
+									  &hctl,
+									  HASH_ELEM | HASH_BLOBS | HASH_CONTEXT);
+			}
+			ft_info = hash_search(ft_htab, &server_id, HASH_ENTER, &found);
+			if (!found)
+			{
+				FdwRoutine *routine = GetFdwRoutineByServerId(server_id);
+				ft_info->server_id = server_id;
+				ft_info->routine = routine;
+				ft_info->frels_list = NIL;
+				Assert(routine->ExecForeignTruncate != NULL);
+			}
+			ft_info->frels_list = lappend(ft_info->frels_list, rel);
+			continue;
+		}
 
 		/*
 		 * Normally, we need a transaction-safe truncation here.  However, if
@@ -1852,6 +1898,25 @@ ExecuteTruncateGuts(List *explicit_rels, List *relids, List *relids_logged,
 		pgstat_count_truncate(rel);
 	}
 
+	/*
+	 * Invocation of FDW handler for each foreign server
+	 */
+	if (ft_htab)
+	{
+		ForeignTruncateInfo *ft_info;
+		HASH_SEQ_STATUS	seq;
+
+		hash_seq_init(&seq, ft_htab);
+		while ((ft_info = hash_seq_search(&seq)) != NULL)
+		{
+			FdwRoutine *routine = ft_info->routine;
+
+			routine->ExecForeignTruncate(ft_info->frels_list,
+										 behavior,
+										 restart_seqs);
+		}
+	}
+
 	/*
 	 * Restart owned sequences if we were asked to.
 	 */
@@ -1939,12 +2004,29 @@ truncate_check_rel(Oid relid, Form_pg_class reltuple)
 	char	   *relname = NameStr(reltuple->relname);
 
 	/*
-	 * Only allow truncate on regular tables and partitioned tables (although,
+	 * Only allow truncate on regular tables, partitioned tables (although,
 	 * the latter are only being included here for the following checks; no
-	 * physical truncation will occur in their case.)
+	 * physical truncation will occur in their case.) and foreign tables
+	 * that support ExecForeignTruncate callback.
 	 */
-	if (reltuple->relkind != RELKIND_RELATION &&
-		reltuple->relkind != RELKIND_PARTITIONED_TABLE)
+	if (reltuple->relkind == RELKIND_FOREIGN_TABLE)
+	{
+		Oid			server_id = GetForeignServerIdByRelId(relid);
+		FdwRoutine *fdwroutine = GetFdwRoutineByServerId(server_id);
+
+		if (!fdwroutine->ExecForeignTruncate)
+		{
+			ForeignServer  *server = GetForeignServer(server_id);
+			ForeignDataWrapper *fdw = GetForeignDataWrapper(server->fdwid);
+
+			ereport(ERROR,
+					(errcode(ERRCODE_WRONG_OBJECT_TYPE),
+					 errmsg("foreign data wrapper \"%s\" on behalf of the foreign table \"%s\" does not support TRUNCATE",
+							fdw->fdwname, relname)));
+		}
+	}
+	else if (reltuple->relkind != RELKIND_RELATION &&
+			 reltuple->relkind != RELKIND_PARTITIONED_TABLE)
 		ereport(ERROR,
 				(errcode(ERRCODE_WRONG_OBJECT_TYPE),
 				 errmsg("\"%s\" is not a table", relname)));
diff --git a/src/include/foreign/fdwapi.h b/src/include/foreign/fdwapi.h
index 95556dfb15..91105939b2 100644
--- a/src/include/foreign/fdwapi.h
+++ b/src/include/foreign/fdwapi.h
@@ -118,6 +118,10 @@ typedef TupleTableSlot *(*IterateDirectModify_function) (ForeignScanState *node)
 
 typedef void (*EndDirectModify_function) (ForeignScanState *node);
 
+typedef void (*ExecForeignTruncate_function) (List *frels_list,
+											  DropBehavior behavior,
+											  bool restart_seqs);
+
 typedef RowMarkType (*GetForeignRowMarkType_function) (RangeTblEntry *rte,
 													   LockClauseStrength strength);
 
@@ -220,6 +224,9 @@ typedef struct FdwRoutine
 	IterateDirectModify_function IterateDirectModify;
 	EndDirectModify_function EndDirectModify;
 
+	/* Functions for truncating foreign tables */
+	ExecForeignTruncate_function ExecForeignTruncate;
+
 	/* Functions for SELECT FOR UPDATE/SHARE row locking */
 	GetForeignRowMarkType_function GetForeignRowMarkType;
 	RefetchForeignRow_function RefetchForeignRow;
diff --git a/src/test/regress/expected/foreign_data.out b/src/test/regress/expected/foreign_data.out
index b9e25820bc..e2c0bcea51 100644
--- a/src/test/regress/expected/foreign_data.out
+++ b/src/test/regress/expected/foreign_data.out
@@ -1807,9 +1807,9 @@ Inherits: fd_pt1
 
 -- TRUNCATE doesn't work on foreign tables, either directly or recursively
 TRUNCATE ft2;  -- ERROR
-ERROR:  "ft2" is not a table
+ERROR:  foreign-data wrapper "dummy" has no handler
 TRUNCATE fd_pt1;  -- ERROR
-ERROR:  "ft2" is not a table
+ERROR:  foreign-data wrapper "dummy" has no handler
 DROP TABLE fd_pt1 CASCADE;
 NOTICE:  drop cascades to foreign table ft2
 -- IMPORT FOREIGN SCHEMA
@@ -2032,9 +2032,9 @@ ALTER FOREIGN TABLE fd_pt2_1 ADD CONSTRAINT fd_pt2chk1 CHECK (c1 > 0);
 ALTER TABLE fd_pt2 ATTACH PARTITION fd_pt2_1 FOR VALUES IN (1);
 -- TRUNCATE doesn't work on foreign tables, either directly or recursively
 TRUNCATE fd_pt2_1;  -- ERROR
-ERROR:  "fd_pt2_1" is not a table
+ERROR:  foreign-data wrapper "dummy" has no handler
 TRUNCATE fd_pt2;  -- ERROR
-ERROR:  "fd_pt2_1" is not a table
+ERROR:  foreign-data wrapper "dummy" has no handler
 DROP FOREIGN TABLE fd_pt2_1;
 DROP TABLE fd_pt2;
 -- foreign table cannot be part of partition tree made of temporary

From ed63df0fdeac43443b8e15709c19fe6c1f38a1f8 Mon Sep 17 00:00:00 2001
From: Michael Paquier <michael@paquier.xyz>
Date: Mon, 20 Jan 2020 22:39:34 +0900
Subject: [PATCH 1/2] Add FDW callback for support of TRUNCATE

---
 src/include/foreign/fdwapi.h               |   7 ++
 src/backend/commands/tablecmds.c           | 110 ++++++++++++++++++++-
 src/test/regress/expected/foreign_data.out |   8 +-
 doc/src/sgml/fdwhandler.sgml               |  36 +++++++
 4 files changed, 153 insertions(+), 8 deletions(-)

diff --git a/src/include/foreign/fdwapi.h b/src/include/foreign/fdwapi.h
index 95556dfb15..0a9f36735e 100644
--- a/src/include/foreign/fdwapi.h
+++ b/src/include/foreign/fdwapi.h
@@ -151,6 +151,10 @@ typedef bool (*AnalyzeForeignTable_function) (Relation relation,
 typedef List *(*ImportForeignSchema_function) (ImportForeignSchemaStmt *stmt,
 											   Oid serverOid);
 
+typedef void (*ExecForeignTruncate_function) (List *frels_list,
+											  DropBehavior behavior,
+											  bool restart_seqs);
+
 typedef Size (*EstimateDSMForeignScan_function) (ForeignScanState *node,
 												 ParallelContext *pcxt);
 typedef void (*InitializeDSMForeignScan_function) (ForeignScanState *node,
@@ -236,6 +240,9 @@ typedef struct FdwRoutine
 	/* Support functions for IMPORT FOREIGN SCHEMA */
 	ImportForeignSchema_function ImportForeignSchema;
 
+	/* Support functions for TRUNCATE */
+	ExecForeignTruncate_function ExecForeignTruncate;
+
 	/* Support functions for parallelism under Gather node */
 	IsForeignScanParallelSafe_function IsForeignScanParallelSafe;
 	EstimateDSMForeignScan_function EstimateDSMForeignScan;
diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index 30b72b6297..f83f88a82f 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -60,6 +60,7 @@
 #include "commands/user.h"
 #include "executor/executor.h"
 #include "foreign/foreign.h"
+#include "foreign/fdwapi.h"
 #include "miscadmin.h"
 #include "nodes/makefuncs.h"
 #include "nodes/nodeFuncs.h"
@@ -295,6 +296,20 @@ struct DropRelationCallbackState
 #define		ATT_FOREIGN_TABLE		0x0020
 #define		ATT_PARTITIONED_INDEX	0x0040
 
+/*
+ * ForeignTruncateInfo
+ *
+ * Information related to truncation of foreign tables.  This
+ * is a single entry part of a hash table using the server OID
+ * as key, with a list of all foreign tables involved.
+ */
+typedef struct
+{
+	Oid		server_oid;
+	List   *frels_list;
+} ForeignTruncateInfo;
+
+
 /*
  * Partition tables are expected to be dropped when the parent partitioned
  * table gets dropped. Hence for partitioning we use AUTO dependency.
@@ -1647,6 +1662,7 @@ ExecuteTruncateGuts(List *explicit_rels, List *relids, List *relids_logged,
 {
 	List	   *rels;
 	List	   *seq_relids = NIL;
+	HTAB	   *ft_htab = NULL;
 	EState	   *estate;
 	ResultRelInfo *resultRelInfos;
 	ResultRelInfo *resultRelInfo;
@@ -1792,6 +1808,57 @@ ExecuteTruncateGuts(List *explicit_rels, List *relids, List *relids_logged,
 		if (rel->rd_rel->relkind == RELKIND_PARTITIONED_TABLE)
 			continue;
 
+		/*
+		 * If truncating a foreign table, the foreign data wrapper
+		 * callback for TRUNCATE is called once for each server
+		 * with a list of all the relations to process linked to this
+		 * server.  The list of relations for each server is saved as
+		 * a single entry of a hash table that uses the server OID as
+		 * lookup key.  Once the full set of lists is built, all the
+		 * entries of the hash table are scanned, and the list of relations
+		 * associated to the server is passed down to the TRUNCATE callback
+		 * of its foreign data wrapper.
+		 */
+		if (rel->rd_rel->relkind == RELKIND_FOREIGN_TABLE)
+		{
+			Oid		frel_oid = RelationGetRelid(rel);
+			Oid		server_oid = GetForeignServerIdByRelId(frel_oid);
+			bool	found;
+			ForeignTruncateInfo *ft_info;
+
+			/* if the hash table does not exist yet, initialize it */
+			if (!ft_htab)
+			{
+				HASHCTL		hctl;
+
+				memset(&hctl, 0, sizeof(HASHCTL));
+				hctl.keysize = sizeof(Oid);
+				hctl.entrysize = sizeof(ForeignTruncateInfo);
+				hctl.hcxt = CurrentMemoryContext;
+
+				ft_htab = hash_create("TRUNCATE for Foreign Tables",
+									  32,	/* start small and extend */
+									  &hctl,
+									  HASH_ELEM | HASH_BLOBS | HASH_CONTEXT);
+			}
+
+			/*
+			 * Look after the entry of the server in the hash table,
+			 * and initialize it if the entry does not exist yet.
+			 */
+			ft_info = hash_search(ft_htab, &server_oid, HASH_ENTER, &found);
+			if (!found)
+			{
+				ft_info->server_oid = server_oid;
+				ft_info->frels_list = NIL;
+
+			}
+
+			/* save the relation in the list */
+			ft_info->frels_list = lappend(ft_info->frels_list, rel);
+			continue;
+		}
+
 		/*
 		 * Normally, we need a transaction-safe truncation here.  However, if
 		 * the table was either created in the current (sub)transaction or has
@@ -1852,6 +1919,29 @@ ExecuteTruncateGuts(List *explicit_rels, List *relids, List *relids_logged,
 		pgstat_count_truncate(rel);
 	}
 
+	/*
+	 * Now go through the hash table, and process each entry associated
+	 * to the servers involved in the TRUNCATE.
+	 */
+	if (ft_htab)
+	{
+		ForeignTruncateInfo *ft_info;
+		HASH_SEQ_STATUS	seq;
+
+		hash_seq_init(&seq, ft_htab);
+
+		while ((ft_info = hash_seq_search(&seq)) != NULL)
+		{
+			FdwRoutine *routine = GetFdwRoutineByServerId(ft_info->server_oid);
+
+			/* truncate_check_rel() has checked that already */
+			Assert(routine->ExecForeignTruncate != NULL);
+			routine->ExecForeignTruncate(ft_info->frels_list,
+										 behavior,
+										 restart_seqs);
+		}
+	}
+
 	/*
 	 * Restart owned sequences if we were asked to.
 	 */
@@ -1939,12 +2029,24 @@ truncate_check_rel(Oid relid, Form_pg_class reltuple)
 	char	   *relname = NameStr(reltuple->relname);
 
 	/*
-	 * Only allow truncate on regular tables and partitioned tables (although,
+	 * Only allow truncate on regular tables, foreign tables using foreign
+	 * data wrappers supporting TRUNCATE and partitioned tables (although,
 	 * the latter are only being included here for the following checks; no
-	 * physical truncation will occur in their case.)
+	 * physical truncation will occur in their case.).
 	 */
-	if (reltuple->relkind != RELKIND_RELATION &&
-		reltuple->relkind != RELKIND_PARTITIONED_TABLE)
+	if (reltuple->relkind == RELKIND_FOREIGN_TABLE)
+	{
+		Oid			server_id = GetForeignServerIdByRelId(relid);
+		FdwRoutine *fdwroutine = GetFdwRoutineByServerId(server_id);
+
+		if (!fdwroutine->ExecForeignTruncate)
+			ereport(ERROR,
+					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+					 errmsg("cannot truncate foreign table \"%s\"",
+							relname)));
+	}
+	else if (reltuple->relkind != RELKIND_RELATION &&
+			 reltuple->relkind != RELKIND_PARTITIONED_TABLE)
 		ereport(ERROR,
 				(errcode(ERRCODE_WRONG_OBJECT_TYPE),
 				 errmsg("\"%s\" is not a table", relname)));
diff --git a/src/test/regress/expected/foreign_data.out b/src/test/regress/expected/foreign_data.out
index b9e25820bc..e2c0bcea51 100644
--- a/src/test/regress/expected/foreign_data.out
+++ b/src/test/regress/expected/foreign_data.out
@@ -1807,9 +1807,9 @@ Inherits: fd_pt1
 
 -- TRUNCATE doesn't work on foreign tables, either directly or recursively
 TRUNCATE ft2;  -- ERROR
-ERROR:  "ft2" is not a table
+ERROR:  foreign-data wrapper "dummy" has no handler
 TRUNCATE fd_pt1;  -- ERROR
-ERROR:  "ft2" is not a table
+ERROR:  foreign-data wrapper "dummy" has no handler
 DROP TABLE fd_pt1 CASCADE;
 NOTICE:  drop cascades to foreign table ft2
 -- IMPORT FOREIGN SCHEMA
@@ -2032,9 +2032,9 @@ ALTER FOREIGN TABLE fd_pt2_1 ADD CONSTRAINT fd_pt2chk1 CHECK (c1 > 0);
 ALTER TABLE fd_pt2 ATTACH PARTITION fd_pt2_1 FOR VALUES IN (1);
 -- TRUNCATE doesn't work on foreign tables, either directly or recursively
 TRUNCATE fd_pt2_1;  -- ERROR
-ERROR:  "fd_pt2_1" is not a table
+ERROR:  foreign-data wrapper "dummy" has no handler
 TRUNCATE fd_pt2;  -- ERROR
-ERROR:  "fd_pt2_1" is not a table
+ERROR:  foreign-data wrapper "dummy" has no handler
 DROP FOREIGN TABLE fd_pt2_1;
 DROP TABLE fd_pt2;
 -- foreign table cannot be part of partition tree made of temporary
diff --git a/doc/src/sgml/fdwhandler.sgml b/doc/src/sgml/fdwhandler.sgml
index 6587678af2..f2416c9074 100644
--- a/doc/src/sgml/fdwhandler.sgml
+++ b/doc/src/sgml/fdwhandler.sgml
@@ -968,6 +968,42 @@ EndDirectModify(ForeignScanState *node);
 
    </sect2>
 
+   <sect2 id="fdw-callbacks-truncate">
+    <title>FDW Routines for Truncate</title>
+<programlisting>
+void
+ExecForeignTruncate(List *frels_list,
+                    DropBehavior behavior, bool restart_seqs);
+</programlisting>
+    <para>
+     Truncate a set of foreign tables defined by
+     <literal>frels_list</literal> belonging to the same foreign server.
+     This optional function is called during execution of
+     <command>TRUNCATE</command> for each foreign server being involved
+     in one <command>TRUNCATE</command> command (note that invocations
+     are not per foreign table).
+    </para>
+    
+    <para>
+     If the <function>ExecForeignTruncate</function> pointer is set to
+     <literal>NULL</literal>, attempts to truncate the foreign table will
+     fail with an error message.
+    </para>
+    
+    <para>
+     <literal>behavior</literal> defines how foreign tables should
+     be truncated, using as possible values <literal>DROP_RESTRICT</literal>
+     and <literal>DROP_CASCADE</literal> (to map with the equivalents of
+     <command>TRUNCATE</command>).
+    </para>
+    
+    <para>
+     <literal>restart_seqs</literal> is set to <literal>true</literal>
+     if <literal>RESTART IDENTITY</literal> was supplied in the
+     <command>TRUNCATE</command>.
+    </para>
+   </sect2>
+
    <sect2 id="fdw-callbacks-row-locking">
     <title>FDW Routines for Row Locking</title>
 
-- 
2.25.0

From 3918ddb188d62accaac7e1dbe5d8459f4fe72b54 Mon Sep 17 00:00:00 2001
From: Michael Paquier <michael@paquier.xyz>
Date: Mon, 20 Jan 2020 22:40:06 +0900
Subject: [PATCH 2/2] Add support for TRUNCATE in postgres_fdw

---
 contrib/postgres_fdw/deparse.c                |  31 ++++
 .../postgres_fdw/expected/postgres_fdw.out    | 144 ++++++++++++++++++
 contrib/postgres_fdw/postgres_fdw.c           |  51 +++++++
 contrib/postgres_fdw/postgres_fdw.h           |   2 +
 contrib/postgres_fdw/sql/postgres_fdw.sql     |  51 +++++++
 5 files changed, 279 insertions(+)

diff --git a/contrib/postgres_fdw/deparse.c b/contrib/postgres_fdw/deparse.c
index a3639e9604..94e8f71d0c 100644
--- a/contrib/postgres_fdw/deparse.c
+++ b/contrib/postgres_fdw/deparse.c
@@ -2098,6 +2098,37 @@ deparseAnalyzeSql(StringInfo buf, Relation rel, List **retrieved_attrs)
 	deparseRelation(buf, rel);
 }
 
+/*
+ * Construct a simple "TRUNCATE rel" statement
+ */
+void
+deparseTruncateSql(StringInfo buf, List *frels_list,
+				   DropBehavior behavior, bool restart_seqs)
+{
+	ListCell   *lc;
+
+	appendStringInfoString(buf, "TRUNCATE ");
+	foreach (lc, frels_list)
+	{
+		Relation	frel = lfirst(lc);
+
+		if (lc != list_head(frels_list))
+			appendStringInfoString(buf, ", ");
+		deparseRelation(buf, frel);
+	}
+	appendStringInfo(buf, " %s IDENTITY",
+					 restart_seqs ? "RESTART" : "CONTINUE");
+	switch (behavior)
+	{
+		case DROP_RESTRICT:
+			appendStringInfoString(buf, " RESTRICT");
+			break;
+		case DROP_CASCADE:
+			appendStringInfoString(buf, " CASCADE");
+			break;
+	}
+}
+
 /*
  * Construct name to use for given column, and emit it into buf.
  * If it has a column_name FDW option, use that instead of attribute name.
diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 84fd3ad2e0..ef10c8f709 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8168,6 +8168,150 @@ select * from rem3;
 
 drop foreign table rem3;
 drop table loc3;
+-- ===================================================================
+-- test for TRUNCATE
+-- ===================================================================
+CREATE TABLE tru_nt (id int, x text);
+CREATE FOREIGN TABLE tru_ft (id int, x text)
+       SERVER loopback OPTIONS (table_name 'tru_nt');
+INSERT INTO tru_nt (SELECT x,md5(x::text) FROM generate_series(1,10) x);
+CREATE TABLE tru_pt (id int, y text) PARTITION BY HASH(id);
+CREATE TABLE tru_pt__p0 PARTITION OF tru_pt
+                        FOR VALUES WITH (MODULUS 2, REMAINDER 0);
+CREATE TABLE __tru_pt__p1 (id int, y text);
+CREATE FOREIGN TABLE tru_pt__p1 PARTITION OF tru_pt
+                                FOR VALUES WITH (MODULUS 2, REMAINDER 1)
+               SERVER loopback OPTIONS (table_name '__tru_pt__p1');
+INSERT INTO tru_pt (SELECT x,md5(x::text) FROM generate_series(11,30) x);
+CREATE TABLE tru_pk (id int primary key, x text);
+INSERT INTO tru_pk (SELECT x,md5((x+1)::text) FROM generate_series(1,10) x);
+CREATE TABLE tru_fk (fkey int references tru_pk(id));
+INSERT INTO tru_fk (SELECT x % 10 + 1 FROM generate_series(1,30) x);
+CREATE FOREIGN TABLE tru_ft_ref (id int, x text)
+       SERVER loopback OPTIONS (table_name 'tru_pk');
+-- normal truncate
+SELECT * FROM tru_ft;
+ id |                x                 
+----+----------------------------------
+  1 | c4ca4238a0b923820dcc509a6f75849b
+  2 | c81e728d9d4c2f636f067f89cc14862c
+  3 | eccbc87e4b5ce2fe28308fd9f2a7baf3
+  4 | a87ff679a2f3e71d9181a67b7542122c
+  5 | e4da3b7fbbce2345d7772b0674a318d5
+  6 | 1679091c5a880faf6fb5e6087eb1b2dc
+  7 | 8f14e45fceea167a5a36dedd4bea2543
+  8 | c9f0f895fb98ab9159f51fd0297e236d
+  9 | 45c48cce2e2d7fbdea1afc51c7c6ad26
+ 10 | d3d9446802a44259755d38e6d163e820
+(10 rows)
+
+TRUNCATE tru_ft;
+SELECT * FROM tru_nt;
+ id | x 
+----+---
+(0 rows)
+
+SELECT * FROM tru_ft;
+ id | x 
+----+---
+(0 rows)
+
+-- partition table mixtured by table and foreign table
+SELECT * FROM tru_pt;
+ id |                y                 
+----+----------------------------------
+ 12 | c20ad4d76fe97759aa27a0c99bff6710
+ 13 | c51ce410c124a10e0db5e4b97fc2af39
+ 14 | aab3238922bcc25a6f606eb525ffdc56
+ 16 | c74d97b01eae257e44aa9d5bade97baf
+ 17 | 70efdf2ec9b086079795c442636b55fb
+ 18 | 6f4922f45568161a8cdf4ad2299f6d23
+ 23 | 37693cfc748049e45d87b8c7d8b9aacd
+ 25 | 8e296a067a37563370ded05f5a3bf3ec
+ 26 | 4e732ced3463d06de0ca9a15b6153677
+ 27 | 02e74f10e0327ad868d138f2b4fdd6f0
+ 28 | 33e75ff09dd601bbe69f351039152189
+ 30 | 34173cb38f07f89ddbebc2ac9128303f
+ 11 | 6512bd43d9caa6e02c990b0a82652dca
+ 15 | 9bf31c7ff062936a96d3c8bd1f8f2ff3
+ 19 | 1f0e3dad99908345f7439f8ffabdffc4
+ 20 | 98f13708210194c475687be6106a3b84
+ 21 | 3c59dc048e8850243be8079a5c74d079
+ 22 | b6d767d2f8ed5d21a44b0e5886680cb9
+ 24 | 1ff1de774005f8da13f42943881c655f
+ 29 | 6ea9ab1baa0efb9e19094440c317e21b
+(20 rows)
+
+TRUNCATE tru_pt;
+SELECT * FROM tru_pt;
+ id | y 
+----+---
+(0 rows)
+
+SELECT * FROM tru_pt__p0;
+ id | y 
+----+---
+(0 rows)
+
+SELECT * FROM tru_pt__p1;
+ id | y 
+----+---
+(0 rows)
+
+SELECT * FROM __tru_pt__p1;
+ id | y 
+----+---
+(0 rows)
+
+-- 'CASCADE' option
+SELECT * FROM tru_ft_ref;
+ id |                x                 
+----+----------------------------------
+  1 | c81e728d9d4c2f636f067f89cc14862c
+  2 | eccbc87e4b5ce2fe28308fd9f2a7baf3
+  3 | a87ff679a2f3e71d9181a67b7542122c
+  4 | e4da3b7fbbce2345d7772b0674a318d5
+  5 | 1679091c5a880faf6fb5e6087eb1b2dc
+  6 | 8f14e45fceea167a5a36dedd4bea2543
+  7 | c9f0f895fb98ab9159f51fd0297e236d
+  8 | 45c48cce2e2d7fbdea1afc51c7c6ad26
+  9 | d3d9446802a44259755d38e6d163e820
+ 10 | 6512bd43d9caa6e02c990b0a82652dca
+(10 rows)
+
+TRUNCATE tru_ft_ref;	-- failed
+ERROR:  cannot truncate a table referenced in a foreign key constraint
+DETAIL:  Table "tru_fk" references "tru_pk".
+HINT:  Truncate table "tru_fk" at the same time, or use TRUNCATE ... CASCADE.
+CONTEXT:  remote SQL command: TRUNCATE public.tru_pk CONTINUE IDENTITY RESTRICT
+TRUNCATE tru_ft_ref CASCADE;
+SELECT * FROM tru_ft_ref;
+ id | x 
+----+---
+(0 rows)
+
+-- truncate two tables at a command
+INSERT INTO tru_ft (SELECT x,md5((x+2)::text) FROM generate_series(1,8) x);
+INSERT INTO tru_ft_ref (SELECT x,md5((x+3)::text) FROM generate_series(1,8) x);
+SELECT * FROM tru_ft a, tru_ft_ref b WHERE a.id = b.id;
+ id |                x                 | id |                x                 
+----+----------------------------------+----+----------------------------------
+  1 | eccbc87e4b5ce2fe28308fd9f2a7baf3 |  1 | a87ff679a2f3e71d9181a67b7542122c
+  2 | a87ff679a2f3e71d9181a67b7542122c |  2 | e4da3b7fbbce2345d7772b0674a318d5
+  3 | e4da3b7fbbce2345d7772b0674a318d5 |  3 | 1679091c5a880faf6fb5e6087eb1b2dc
+  4 | 1679091c5a880faf6fb5e6087eb1b2dc |  4 | 8f14e45fceea167a5a36dedd4bea2543
+  5 | 8f14e45fceea167a5a36dedd4bea2543 |  5 | c9f0f895fb98ab9159f51fd0297e236d
+  6 | c9f0f895fb98ab9159f51fd0297e236d |  6 | 45c48cce2e2d7fbdea1afc51c7c6ad26
+  7 | 45c48cce2e2d7fbdea1afc51c7c6ad26 |  7 | d3d9446802a44259755d38e6d163e820
+  8 | d3d9446802a44259755d38e6d163e820 |  8 | 6512bd43d9caa6e02c990b0a82652dca
+(8 rows)
+
+TRUNCATE tru_ft, tru_ft_ref CASCADE;
+SELECT * FROM tru_ft a, tru_ft_ref b WHERE a.id = b.id;
+ id | x | id | x 
+----+---+----+---
+(0 rows)
+
 -- ===================================================================
 -- test IMPORT FOREIGN SCHEMA
 -- ===================================================================
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index 2175dff824..ded54ab5e9 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -373,6 +373,9 @@ static void postgresExplainForeignModify(ModifyTableState *mtstate,
 										 ExplainState *es);
 static void postgresExplainDirectModify(ForeignScanState *node,
 										ExplainState *es);
+static void postgresExecForeignTruncate(List *frels_list,
+										DropBehavior behavior,
+										bool restart_seqs);
 static bool postgresAnalyzeForeignTable(Relation relation,
 										AcquireSampleRowsFunc *func,
 										BlockNumber *totalpages);
@@ -546,6 +549,9 @@ postgres_fdw_handler(PG_FUNCTION_ARGS)
 	routine->ExplainForeignModify = postgresExplainForeignModify;
 	routine->ExplainDirectModify = postgresExplainDirectModify;
 
+	/* Support function for TRUNCATE */
+	routine->ExecForeignTruncate = postgresExecForeignTruncate;
+
 	/* Support functions for ANALYZE */
 	routine->AnalyzeForeignTable = postgresAnalyzeForeignTable;
 
@@ -2656,6 +2662,51 @@ postgresExplainDirectModify(ForeignScanState *node, ExplainState *es)
 	}
 }
 
+/*
+ * postgresExecForeignTruncate
+ *		It propagates TRUNCATE command to the remote host inside of the
+ *		transaction block.
+ */
+static void
+postgresExecForeignTruncate(List *frels_list,
+							DropBehavior behavior,
+							bool restart_seqs)
+{
+	Oid				server_id = InvalidOid;
+	UserMapping	   *user = NULL;
+	PGconn		   *conn = NULL;
+	PGresult	   *res;
+	StringInfoData	sql;
+	ListCell	   *lc;
+
+	/* pick up remote connection, and sanity checks */
+	foreach (lc, frels_list)
+	{
+		Relation	frel = lfirst(lc);
+		Oid			frel_oid = RelationGetRelid(frel);
+
+		if (!OidIsValid(server_id))
+		{
+			server_id = GetForeignServerIdByRelId(frel_oid);
+			user = GetUserMapping(GetUserId(), server_id);
+			conn = GetConnection(user, false);
+		}
+		else if (server_id != GetForeignServerIdByRelId(frel_oid))
+			elog(ERROR, "Bug? inconsistent Server-IDs were supplied");
+	}
+	/* set up remote query */
+	initStringInfo(&sql);
+	deparseTruncateSql(&sql, frels_list, behavior, restart_seqs);
+	/* run remote query */
+	if (!PQsendQuery(conn, sql.data))
+		pgfdw_report_error(ERROR, NULL, conn, false, sql.data);
+	res = pgfdw_get_result(conn, sql.data);
+	if (PQresultStatus(res) != PGRES_COMMAND_OK)
+		pgfdw_report_error(ERROR, res, conn, true, sql.data);
+	/* clean-up */
+	PQclear(res);
+	pfree(sql.data);
+}
 
 /*
  * estimate_path_cost_size
diff --git a/contrib/postgres_fdw/postgres_fdw.h b/contrib/postgres_fdw/postgres_fdw.h
index eef410db39..1d75bf363a 100644
--- a/contrib/postgres_fdw/postgres_fdw.h
+++ b/contrib/postgres_fdw/postgres_fdw.h
@@ -190,6 +190,8 @@ extern void deparseDirectDeleteSql(StringInfo buf, PlannerInfo *root,
 extern void deparseAnalyzeSizeSql(StringInfo buf, Relation rel);
 extern void deparseAnalyzeSql(StringInfo buf, Relation rel,
 							  List **retrieved_attrs);
+extern void deparseTruncateSql(StringInfo buf, List *frels_list,
+							   DropBehavior behavior, bool restart_seqs);
 extern void deparseStringLiteral(StringInfo buf, const char *val);
 extern Expr *find_em_expr_for_rel(EquivalenceClass *ec, RelOptInfo *rel);
 extern Expr *find_em_expr_for_input_target(PlannerInfo *root,
diff --git a/contrib/postgres_fdw/sql/postgres_fdw.sql b/contrib/postgres_fdw/sql/postgres_fdw.sql
index acd7275c72..95c6e45975 100644
--- a/contrib/postgres_fdw/sql/postgres_fdw.sql
+++ b/contrib/postgres_fdw/sql/postgres_fdw.sql
@@ -2287,6 +2287,57 @@ select * from rem3;
 drop foreign table rem3;
 drop table loc3;
 
+-- ===================================================================
+-- test for TRUNCATE
+-- ===================================================================
+CREATE TABLE tru_nt (id int, x text);
+CREATE FOREIGN TABLE tru_ft (id int, x text)
+       SERVER loopback OPTIONS (table_name 'tru_nt');
+INSERT INTO tru_nt (SELECT x,md5(x::text) FROM generate_series(1,10) x);
+
+CREATE TABLE tru_pt (id int, y text) PARTITION BY HASH(id);
+CREATE TABLE tru_pt__p0 PARTITION OF tru_pt
+                        FOR VALUES WITH (MODULUS 2, REMAINDER 0);
+CREATE TABLE __tru_pt__p1 (id int, y text);
+CREATE FOREIGN TABLE tru_pt__p1 PARTITION OF tru_pt
+                                FOR VALUES WITH (MODULUS 2, REMAINDER 1)
+               SERVER loopback OPTIONS (table_name '__tru_pt__p1');
+INSERT INTO tru_pt (SELECT x,md5(x::text) FROM generate_series(11,30) x);
+
+CREATE TABLE tru_pk (id int primary key, x text);
+INSERT INTO tru_pk (SELECT x,md5((x+1)::text) FROM generate_series(1,10) x);
+CREATE TABLE tru_fk (fkey int references tru_pk(id));
+INSERT INTO tru_fk (SELECT x % 10 + 1 FROM generate_series(1,30) x);
+CREATE FOREIGN TABLE tru_ft_ref (id int, x text)
+       SERVER loopback OPTIONS (table_name 'tru_pk');
+
+-- normal truncate
+SELECT * FROM tru_ft;
+TRUNCATE tru_ft;
+SELECT * FROM tru_nt;
+SELECT * FROM tru_ft;
+
+-- partition table mixtured by table and foreign table
+SELECT * FROM tru_pt;
+TRUNCATE tru_pt;
+SELECT * FROM tru_pt;
+SELECT * FROM tru_pt__p0;
+SELECT * FROM tru_pt__p1;
+SELECT * FROM __tru_pt__p1;
+
+-- 'CASCADE' option
+SELECT * FROM tru_ft_ref;
+TRUNCATE tru_ft_ref;	-- failed
+TRUNCATE tru_ft_ref CASCADE;
+SELECT * FROM tru_ft_ref;
+
+-- truncate two tables at a command
+INSERT INTO tru_ft (SELECT x,md5((x+2)::text) FROM generate_series(1,8) x);
+INSERT INTO tru_ft_ref (SELECT x,md5((x+3)::text) FROM generate_series(1,8) x);
+SELECT * FROM tru_ft a, tru_ft_ref b WHERE a.id = b.id;
+TRUNCATE tru_ft, tru_ft_ref CASCADE;
+SELECT * FROM tru_ft a, tru_ft_ref b WHERE a.id = b.id;
+
 -- ===================================================================
 -- test IMPORT FOREIGN SCHEMA
 -- ===================================================================
-- 
2.25.0

From dce70bca1242372c4d36c9d84973adffa90e5bdb Mon Sep 17 00:00:00 2001
From: Michael Paquier <michael@paquier.xyz>
Date: Tue, 21 Jan 2020 15:32:41 +0900
Subject: [PATCH] Add FDW callback for support of TRUNCATE

---
 src/include/foreign/fdwapi.h               |   7 ++
 src/backend/commands/tablecmds.c           | 113 ++++++++++++++++++++-
 src/test/regress/expected/foreign_data.out |   8 +-
 doc/src/sgml/fdwhandler.sgml               |  36 +++++++
 src/tools/pgindent/typedefs.list           |   1 +
 5 files changed, 156 insertions(+), 9 deletions(-)

diff --git a/src/include/foreign/fdwapi.h b/src/include/foreign/fdwapi.h
index 95556dfb15..0a9f36735e 100644
--- a/src/include/foreign/fdwapi.h
+++ b/src/include/foreign/fdwapi.h
@@ -151,6 +151,10 @@ typedef bool (*AnalyzeForeignTable_function) (Relation relation,
 typedef List *(*ImportForeignSchema_function) (ImportForeignSchemaStmt *stmt,
 											   Oid serverOid);
 
+typedef void (*ExecForeignTruncate_function) (List *frels_list,
+											  DropBehavior behavior,
+											  bool restart_seqs);
+
 typedef Size (*EstimateDSMForeignScan_function) (ForeignScanState *node,
 												 ParallelContext *pcxt);
 typedef void (*InitializeDSMForeignScan_function) (ForeignScanState *node,
@@ -236,6 +240,9 @@ typedef struct FdwRoutine
 	/* Support functions for IMPORT FOREIGN SCHEMA */
 	ImportForeignSchema_function ImportForeignSchema;
 
+	/* Support functions for TRUNCATE */
+	ExecForeignTruncate_function ExecForeignTruncate;
+
 	/* Support functions for parallelism under Gather node */
 	IsForeignScanParallelSafe_function IsForeignScanParallelSafe;
 	EstimateDSMForeignScan_function EstimateDSMForeignScan;
diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index 30b72b6297..2c575668c2 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -59,6 +59,7 @@
 #include "commands/typecmds.h"
 #include "commands/user.h"
 #include "executor/executor.h"
+#include "foreign/fdwapi.h"
 #include "foreign/foreign.h"
 #include "miscadmin.h"
 #include "nodes/makefuncs.h"
@@ -295,6 +296,21 @@ struct DropRelationCallbackState
 #define		ATT_FOREIGN_TABLE		0x0020
 #define		ATT_PARTITIONED_INDEX	0x0040
 
+/*
+ * ForeignTruncateInfo
+ *
+ * Information related to truncation of foreign tables.  This is used for
+ * the elements in a hash table that uses the server OID as lookup key,
+ * and includes a per-server list of all foreign tables involved in the
+ * truncation.
+ */
+typedef struct
+{
+	Oid			server_oid;
+	List	   *frels_list;
+} ForeignTruncateInfo;
+
+
 /*
  * Partition tables are expected to be dropped when the parent partitioned
  * table gets dropped. Hence for partitioning we use AUTO dependency.
@@ -1647,6 +1663,7 @@ ExecuteTruncateGuts(List *explicit_rels, List *relids, List *relids_logged,
 {
 	List	   *rels;
 	List	   *seq_relids = NIL;
+	HTAB	   *ft_htab = NULL;
 	EState	   *estate;
 	ResultRelInfo *resultRelInfos;
 	ResultRelInfo *resultRelInfo;
@@ -1792,6 +1809,56 @@ ExecuteTruncateGuts(List *explicit_rels, List *relids, List *relids_logged,
 		if (rel->rd_rel->relkind == RELKIND_PARTITIONED_TABLE)
 			continue;
 
+		/*
+		 * If truncating a foreign table, the foreign data wrapper callback
+		 * for TRUNCATE is called once for each server with a list of all the
+		 * relations to process linked to this server.  The list of relations
+		 * for each server is saved as a single entry in a hash table that
+		 * uses the server OID as lookup key.  Once the full set of lists is
+		 * built, all the entries of the hash table are scanned, and the list
+		 * of relations associated to the server is passed down to the
+		 * TRUNCATE callback of its foreign data wrapper.
+		 */
+		if (rel->rd_rel->relkind == RELKIND_FOREIGN_TABLE)
+		{
+			Oid			frel_oid = RelationGetRelid(rel);
+			Oid			server_oid = GetForeignServerIdByRelId(frel_oid);
+			bool		found;
+			ForeignTruncateInfo *ft_info;
+
+			/* if the hash table does not exist yet, initialize it */
+			if (!ft_htab)
+			{
+				HASHCTL		hctl;
+
+				memset(&hctl, 0, sizeof(HASHCTL));
+				hctl.keysize = sizeof(Oid);
+				hctl.entrysize = sizeof(ForeignTruncateInfo);
+				hctl.hcxt = CurrentMemoryContext;
+
+				ft_htab = hash_create("TRUNCATE for Foreign Tables",
+									  32,	/* start small and extend */
+									  &hctl,
+									  HASH_ELEM | HASH_BLOBS | HASH_CONTEXT);
+			}
+
+			/*
+			 * Look after the entry of the server in the hash table, and
+			 * initialize it if the entry does not exist yet.
+			 */
+			ft_info = hash_search(ft_htab, &server_oid, HASH_ENTER, &found);
+			if (!found)
+			{
+				ft_info->server_oid = server_oid;
+				ft_info->frels_list = NIL;
+
+			}
+
+			/* save the relation in the list */
+			ft_info->frels_list = lappend(ft_info->frels_list, rel);
+			continue;
+		}
+
 		/*
 		 * Normally, we need a transaction-safe truncation here.  However, if
 		 * the table was either created in the current (sub)transaction or has
@@ -1852,6 +1919,30 @@ ExecuteTruncateGuts(List *explicit_rels, List *relids, List *relids_logged,
 		pgstat_count_truncate(rel);
 	}
 
+	/*
+	 * Now go through the hash table, and process each entry associated to the
+	 * servers involved in the TRUNCATE.
+	 */
+	if (ft_htab)
+	{
+		ForeignTruncateInfo *ft_info;
+		HASH_SEQ_STATUS seq;
+
+		hash_seq_init(&seq, ft_htab);
+
+		while ((ft_info = hash_seq_search(&seq)) != NULL)
+		{
+			FdwRoutine *routine = GetFdwRoutineByServerId(ft_info->server_oid);
+
+			/* truncate_check_rel() has checked that already */
+			Assert(routine->ExecForeignTruncate != NULL);
+
+			routine->ExecForeignTruncate(ft_info->frels_list,
+										 behavior,
+										 restart_seqs);
+		}
+	}
+
 	/*
 	 * Restart owned sequences if we were asked to.
 	 */
@@ -1939,12 +2030,24 @@ truncate_check_rel(Oid relid, Form_pg_class reltuple)
 	char	   *relname = NameStr(reltuple->relname);
 
 	/*
-	 * Only allow truncate on regular tables and partitioned tables (although,
-	 * the latter are only being included here for the following checks; no
-	 * physical truncation will occur in their case.)
+	 * Only allow truncate on regular tables, foreign tables using foreign
+	 * data wrappers supporting TRUNCATE and partitioned tables (although, the
+	 * latter are only being included here for the following checks; no
+	 * physical truncation will occur in their case.).
 	 */
-	if (reltuple->relkind != RELKIND_RELATION &&
-		reltuple->relkind != RELKIND_PARTITIONED_TABLE)
+	if (reltuple->relkind == RELKIND_FOREIGN_TABLE)
+	{
+		Oid			server_id = GetForeignServerIdByRelId(relid);
+		FdwRoutine *fdwroutine = GetFdwRoutineByServerId(server_id);
+
+		if (!fdwroutine->ExecForeignTruncate)
+			ereport(ERROR,
+					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+					 errmsg("cannot truncate foreign table \"%s\"",
+							relname)));
+	}
+	else if (reltuple->relkind != RELKIND_RELATION &&
+			 reltuple->relkind != RELKIND_PARTITIONED_TABLE)
 		ereport(ERROR,
 				(errcode(ERRCODE_WRONG_OBJECT_TYPE),
 				 errmsg("\"%s\" is not a table", relname)));
diff --git a/src/test/regress/expected/foreign_data.out b/src/test/regress/expected/foreign_data.out
index b9e25820bc..e2c0bcea51 100644
--- a/src/test/regress/expected/foreign_data.out
+++ b/src/test/regress/expected/foreign_data.out
@@ -1807,9 +1807,9 @@ Inherits: fd_pt1
 
 -- TRUNCATE doesn't work on foreign tables, either directly or recursively
 TRUNCATE ft2;  -- ERROR
-ERROR:  "ft2" is not a table
+ERROR:  foreign-data wrapper "dummy" has no handler
 TRUNCATE fd_pt1;  -- ERROR
-ERROR:  "ft2" is not a table
+ERROR:  foreign-data wrapper "dummy" has no handler
 DROP TABLE fd_pt1 CASCADE;
 NOTICE:  drop cascades to foreign table ft2
 -- IMPORT FOREIGN SCHEMA
@@ -2032,9 +2032,9 @@ ALTER FOREIGN TABLE fd_pt2_1 ADD CONSTRAINT fd_pt2chk1 CHECK (c1 > 0);
 ALTER TABLE fd_pt2 ATTACH PARTITION fd_pt2_1 FOR VALUES IN (1);
 -- TRUNCATE doesn't work on foreign tables, either directly or recursively
 TRUNCATE fd_pt2_1;  -- ERROR
-ERROR:  "fd_pt2_1" is not a table
+ERROR:  foreign-data wrapper "dummy" has no handler
 TRUNCATE fd_pt2;  -- ERROR
-ERROR:  "fd_pt2_1" is not a table
+ERROR:  foreign-data wrapper "dummy" has no handler
 DROP FOREIGN TABLE fd_pt2_1;
 DROP TABLE fd_pt2;
 -- foreign table cannot be part of partition tree made of temporary
diff --git a/doc/src/sgml/fdwhandler.sgml b/doc/src/sgml/fdwhandler.sgml
index 6587678af2..f2416c9074 100644
--- a/doc/src/sgml/fdwhandler.sgml
+++ b/doc/src/sgml/fdwhandler.sgml
@@ -968,6 +968,42 @@ EndDirectModify(ForeignScanState *node);
 
    </sect2>
 
+   <sect2 id="fdw-callbacks-truncate">
+    <title>FDW Routines for Truncate</title>
+<programlisting>
+void
+ExecForeignTruncate(List *frels_list,
+                    DropBehavior behavior, bool restart_seqs);
+</programlisting>
+    <para>
+     Truncate a set of foreign tables defined by
+     <literal>frels_list</literal> belonging to the same foreign server.
+     This optional function is called during execution of
+     <command>TRUNCATE</command> for each foreign server being involved
+     in one <command>TRUNCATE</command> command (note that invocations
+     are not per foreign table).
+    </para>
+    
+    <para>
+     If the <function>ExecForeignTruncate</function> pointer is set to
+     <literal>NULL</literal>, attempts to truncate the foreign table will
+     fail with an error message.
+    </para>
+    
+    <para>
+     <literal>behavior</literal> defines how foreign tables should
+     be truncated, using as possible values <literal>DROP_RESTRICT</literal>
+     and <literal>DROP_CASCADE</literal> (to map with the equivalents of
+     <command>TRUNCATE</command>).
+    </para>
+    
+    <para>
+     <literal>restart_seqs</literal> is set to <literal>true</literal>
+     if <literal>RESTART IDENTITY</literal> was supplied in the
+     <command>TRUNCATE</command>.
+    </para>
+   </sect2>
+
    <sect2 id="fdw-callbacks-row-locking">
     <title>FDW Routines for Row Locking</title>
 
diff --git a/src/tools/pgindent/typedefs.list b/src/tools/pgindent/typedefs.list
index e216de9570..ef2bd90db1 100644
--- a/src/tools/pgindent/typedefs.list
+++ b/src/tools/pgindent/typedefs.list
@@ -686,6 +686,7 @@ ForeignScanState
 ForeignServer
 ForeignServerInfo
 ForeignTable
+ForeignTruncateInfo
 ForkNumber
 FormData_pg_aggregate
 FormData_pg_am
-- 
2.25.0

 contrib/postgres_fdw/deparse.c                 |  38 ++++
 contrib/postgres_fdw/expected/postgres_fdw.out | 235 ++++++++++++++++++++++++-
 contrib/postgres_fdw/option.c                  |   6 +-
 contrib/postgres_fdw/postgres_fdw.c            |  85 +++++++++
 contrib/postgres_fdw/postgres_fdw.h            |   5 +
 contrib/postgres_fdw/sql/postgres_fdw.sql      |  90 ++++++++++
 doc/src/sgml/fdwhandler.sgml                   |  40 +++++
 doc/src/sgml/postgres-fdw.sgml                 |  30 +++-
 src/backend/commands/tablecmds.c               | 134 +++++++++++++-
 src/backend/replication/logical/worker.c       |  10 +-
 src/include/commands/tablecmds.h               |   8 +-
 src/include/foreign/fdwapi.h                   |   8 +
 src/test/regress/expected/foreign_data.out     |   8 +-
 src/tools/pgindent/typedefs.list               |   1 +
 14 files changed, 676 insertions(+), 22 deletions(-)

diff --git a/contrib/postgres_fdw/deparse.c b/contrib/postgres_fdw/deparse.c
index ad37a74221..1dc92e4df0 100644
--- a/contrib/postgres_fdw/deparse.c
+++ b/contrib/postgres_fdw/deparse.c
@@ -2114,6 +2114,44 @@ deparseAnalyzeSql(StringInfo buf, Relation rel, List **retrieved_attrs)
 	deparseRelation(buf, rel);
 }
 
+/*
+ * Construct a simple "TRUNCATE rel" statement
+ */
+void
+deparseTruncateSql(StringInfo buf,
+				   List *frels_list,
+				   List *frels_extra,
+				   DropBehavior behavior,
+				   bool restart_seqs)
+{
+	ListCell   *lc1, *lc2;
+
+	appendStringInfoString(buf, "TRUNCATE ");
+	forboth (lc1, frels_list,
+			 lc2, frels_extra)
+	{
+		Relation	frel = lfirst(lc1);
+		int			extra = lfirst_int(lc2);
+
+		if (lc1 != list_head(frels_list))
+			appendStringInfoString(buf, ", ");
+		if (extra != 0)
+			appendStringInfoString(buf, "ONLY ");
+		deparseRelation(buf, frel);
+	}
+	appendStringInfo(buf, " %s IDENTITY",
+					 restart_seqs ? "RESTART" : "CONTINUE");
+	switch (behavior)
+	{
+		case DROP_RESTRICT:
+			appendStringInfoString(buf, " RESTRICT");
+			break;
+		case DROP_CASCADE:
+			appendStringInfoString(buf, " CASCADE");
+			break;
+	}
+}
+
 /*
  * Construct name to use for given column, and emit it into buf.
  * If it has a column_name FDW option, use that instead of attribute name.
diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62c2697920..37004cd3b2 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8199,6 +8199,239 @@ select * from rem3;
 
 drop foreign table rem3;
 drop table loc3;
+-- ===================================================================
+-- test for TRUNCATE
+-- ===================================================================
+CREATE TABLE tru_rtable0 (id int primary key, x text);
+CREATE TABLE tru_rtable1 (id int primary key, y text);
+CREATE FOREIGN TABLE tru_ftable (id int, x text)
+       SERVER loopback OPTIONS (table_name 'tru_rtable0');
+INSERT INTO tru_rtable0 (SELECT x,md5(x::text) FROM generate_series(1,10) x);
+CREATE TABLE tru_ptable (id int, y text) PARTITION BY HASH(id);
+CREATE TABLE tru_ptable__p0 PARTITION OF tru_ptable
+                            FOR VALUES WITH (MODULUS 2, REMAINDER 0);
+CREATE FOREIGN TABLE tru_ftable__p1 PARTITION OF tru_ptable
+                                    FOR VALUES WITH (MODULUS 2, REMAINDER 1)
+       SERVER loopback OPTIONS (table_name 'tru_rtable1');
+INSERT INTO tru_ptable (SELECT x,md5(x::text) FROM generate_series(11,20) x);
+CREATE TABLE tru_pk_table(id int primary key, z text);
+CREATE TABLE tru_fk_table(fkey int references tru_pk_table(id));
+INSERT INTO tru_pk_table (SELECT x,md5((x+1)::text) FROM generate_series(1,10) x);
+INSERT INTO tru_fk_table (SELECT x % 10 + 1 FROM generate_series(5,25) x);
+CREATE FOREIGN TABLE tru_pk_ftable (id int, z text)
+       SERVER loopback OPTIONS (table_name 'tru_pk_table');
+CREATE TABLE tru_rtable_parent (id int, a text);
+CREATE TABLE tru_rtable_child (id int, a text);
+CREATE FOREIGN TABLE tru_ftable_parent (id int, a text)
+       SERVER loopback OPTIONS (table_name 'tru_rtable_parent');
+CREATE FOREIGN TABLE tru_ftable_child () INHERITS (tru_ftable_parent)
+       SERVER loopback OPTIONS (table_name 'tru_rtable_child');
+INSERT INTO tru_rtable_parent (SELECT x, md5(x::text) FROM generate_series(1,8) x);
+INSERT INTO tru_rtable_child  (SELECT x, md5(x::text) FROM generate_series(10, 18) x);
+-- normal truncate
+SELECT * FROM tru_ftable;
+ id |                x                 
+----+----------------------------------
+  1 | c4ca4238a0b923820dcc509a6f75849b
+  2 | c81e728d9d4c2f636f067f89cc14862c
+  3 | eccbc87e4b5ce2fe28308fd9f2a7baf3
+  4 | a87ff679a2f3e71d9181a67b7542122c
+  5 | e4da3b7fbbce2345d7772b0674a318d5
+  6 | 1679091c5a880faf6fb5e6087eb1b2dc
+  7 | 8f14e45fceea167a5a36dedd4bea2543
+  8 | c9f0f895fb98ab9159f51fd0297e236d
+  9 | 45c48cce2e2d7fbdea1afc51c7c6ad26
+ 10 | d3d9446802a44259755d38e6d163e820
+(10 rows)
+
+TRUNCATE tru_ftable;
+SELECT * FROM tru_rtable0;		-- empty
+ id | x 
+----+---
+(0 rows)
+
+SELECT * FROM tru_ftable;		-- empty
+ id | x 
+----+---
+(0 rows)
+
+-- 'truncatable' option
+ALTER SERVER loopback OPTIONS (ADD truncatable 'false');
+TRUNCATE tru_ftable;			-- error
+ERROR:  truncate on "tru_ftable" is prohibited
+ALTER SERVER loopback OPTIONS (DROP truncatable);
+ALTER FOREIGN TABLE tru_ftable OPTIONS (ADD truncatable 'false');
+TRUNCATE tru_ftable;			-- error
+ERROR:  truncate on "tru_ftable" is prohibited
+ALTER FOREIGN TABLE tru_ftable OPTIONS (SET truncatable 'true');
+TRUNCATE tru_ftable;			-- accepted
+-- partition table mixtured by table and foreign table
+SELECT * FROM tru_ptable;
+ id |                y                 
+----+----------------------------------
+ 12 | c20ad4d76fe97759aa27a0c99bff6710
+ 13 | c51ce410c124a10e0db5e4b97fc2af39
+ 14 | aab3238922bcc25a6f606eb525ffdc56
+ 16 | c74d97b01eae257e44aa9d5bade97baf
+ 17 | 70efdf2ec9b086079795c442636b55fb
+ 18 | 6f4922f45568161a8cdf4ad2299f6d23
+ 11 | 6512bd43d9caa6e02c990b0a82652dca
+ 15 | 9bf31c7ff062936a96d3c8bd1f8f2ff3
+ 19 | 1f0e3dad99908345f7439f8ffabdffc4
+ 20 | 98f13708210194c475687be6106a3b84
+(10 rows)
+
+TRUNCATE tru_ptable;
+SELECT * FROM tru_ptable;		-- empty
+ id | y 
+----+---
+(0 rows)
+
+SELECT * FROM tru_ptable__p0;	-- empty
+ id | y 
+----+---
+(0 rows)
+
+SELECT * FROM tru_ftable__p1;	-- empty
+ id | y 
+----+---
+(0 rows)
+
+SELECT * FROM tru_rtable1;		-- empty
+ id | y 
+----+---
+(0 rows)
+
+-- 'CASCADE' option
+SELECT * FROM tru_pk_ftable;
+ id |                z                 
+----+----------------------------------
+  1 | c81e728d9d4c2f636f067f89cc14862c
+  2 | eccbc87e4b5ce2fe28308fd9f2a7baf3
+  3 | a87ff679a2f3e71d9181a67b7542122c
+  4 | e4da3b7fbbce2345d7772b0674a318d5
+  5 | 1679091c5a880faf6fb5e6087eb1b2dc
+  6 | 8f14e45fceea167a5a36dedd4bea2543
+  7 | c9f0f895fb98ab9159f51fd0297e236d
+  8 | 45c48cce2e2d7fbdea1afc51c7c6ad26
+  9 | d3d9446802a44259755d38e6d163e820
+ 10 | 6512bd43d9caa6e02c990b0a82652dca
+(10 rows)
+
+TRUNCATE tru_pk_ftable;	-- failed by FK reference
+ERROR:  cannot truncate a table referenced in a foreign key constraint
+DETAIL:  Table "tru_fk_table" references "tru_pk_table".
+HINT:  Truncate table "tru_fk_table" at the same time, or use TRUNCATE ... CASCADE.
+CONTEXT:  remote SQL command: TRUNCATE public.tru_pk_table CONTINUE IDENTITY RESTRICT
+TRUNCATE tru_pk_ftable CASCADE;
+SELECT * FROM tru_pk_ftable;
+ id | z 
+----+---
+(0 rows)
+
+SELECT * FROM tru_fk_table;		-- also truncated
+ fkey 
+------
+(0 rows)
+
+-- truncate two tables at a command
+INSERT INTO tru_ftable (SELECT x,md5((x+2)::text) FROM generate_series(1,8) x);
+INSERT INTO tru_pk_ftable (SELECT x,md5((x+3)::text) FROM generate_series(3,10) x);
+SELECT * FROM tru_ftable a FULL OUTER JOIN tru_pk_ftable b ON a.id = b.id;
+ id |                x                 | id |                z                 
+----+----------------------------------+----+----------------------------------
+  1 | eccbc87e4b5ce2fe28308fd9f2a7baf3 |    | 
+  2 | a87ff679a2f3e71d9181a67b7542122c |    | 
+  3 | e4da3b7fbbce2345d7772b0674a318d5 |  3 | 1679091c5a880faf6fb5e6087eb1b2dc
+  4 | 1679091c5a880faf6fb5e6087eb1b2dc |  4 | 8f14e45fceea167a5a36dedd4bea2543
+  5 | 8f14e45fceea167a5a36dedd4bea2543 |  5 | c9f0f895fb98ab9159f51fd0297e236d
+  6 | c9f0f895fb98ab9159f51fd0297e236d |  6 | 45c48cce2e2d7fbdea1afc51c7c6ad26
+  7 | 45c48cce2e2d7fbdea1afc51c7c6ad26 |  7 | d3d9446802a44259755d38e6d163e820
+  8 | d3d9446802a44259755d38e6d163e820 |  8 | 6512bd43d9caa6e02c990b0a82652dca
+    |                                  |  9 | c20ad4d76fe97759aa27a0c99bff6710
+    |                                  | 10 | c51ce410c124a10e0db5e4b97fc2af39
+(10 rows)
+
+TRUNCATE tru_ftable, tru_pk_ftable CASCADE;
+SELECT * FROM tru_ftable a FULL OUTER JOIN tru_pk_ftable b ON a.id = b.id;
+ id | x | id | z 
+----+---+----+---
+(0 rows)
+
+-- truncate with ONLY clause
+TRUNCATE ONLY tru_ftable_parent;
+SELECT * FROM tru_ftable_parent;
+ id |                a                 
+----+----------------------------------
+ 10 | d3d9446802a44259755d38e6d163e820
+ 11 | 6512bd43d9caa6e02c990b0a82652dca
+ 12 | c20ad4d76fe97759aa27a0c99bff6710
+ 13 | c51ce410c124a10e0db5e4b97fc2af39
+ 14 | aab3238922bcc25a6f606eb525ffdc56
+ 15 | 9bf31c7ff062936a96d3c8bd1f8f2ff3
+ 16 | c74d97b01eae257e44aa9d5bade97baf
+ 17 | 70efdf2ec9b086079795c442636b55fb
+ 18 | 6f4922f45568161a8cdf4ad2299f6d23
+(9 rows)
+
+TRUNCATE tru_ftable_parent;
+SELECT * FROM tru_ftable_parent;
+ id | a 
+----+---
+(0 rows)
+
+-- in case when remote table has inherited children
+CREATE TABLE tru_rtable0_child () INHERITS (tru_rtable0);
+INSERT INTO tru_rtable0 (SELECT x,md5(x::text) FROM generate_series(5,9) x);
+INSERT INTO tru_rtable0_child (SELECT x,md5(x::text) FROM generate_series(10,14) x);
+SELECT * FROM tru_ftable;
+ id |                x                 
+----+----------------------------------
+  5 | e4da3b7fbbce2345d7772b0674a318d5
+  6 | 1679091c5a880faf6fb5e6087eb1b2dc
+  7 | 8f14e45fceea167a5a36dedd4bea2543
+  8 | c9f0f895fb98ab9159f51fd0297e236d
+  9 | 45c48cce2e2d7fbdea1afc51c7c6ad26
+ 10 | d3d9446802a44259755d38e6d163e820
+ 11 | 6512bd43d9caa6e02c990b0a82652dca
+ 12 | c20ad4d76fe97759aa27a0c99bff6710
+ 13 | c51ce410c124a10e0db5e4b97fc2af39
+ 14 | aab3238922bcc25a6f606eb525ffdc56
+(10 rows)
+
+TRUNCATE ONLY tru_ftable;		-- truncate only parent portion
+SELECT * FROM tru_ftable;
+ id |                x                 
+----+----------------------------------
+ 10 | d3d9446802a44259755d38e6d163e820
+ 11 | 6512bd43d9caa6e02c990b0a82652dca
+ 12 | c20ad4d76fe97759aa27a0c99bff6710
+ 13 | c51ce410c124a10e0db5e4b97fc2af39
+ 14 | aab3238922bcc25a6f606eb525ffdc56
+(5 rows)
+
+INSERT INTO tru_rtable0 (SELECT x,md5(x::text) FROM generate_series(21,25) x);
+SELECT * FROM tru_ftable;
+ id |                x                 
+----+----------------------------------
+ 21 | 3c59dc048e8850243be8079a5c74d079
+ 22 | b6d767d2f8ed5d21a44b0e5886680cb9
+ 23 | 37693cfc748049e45d87b8c7d8b9aacd
+ 24 | 1ff1de774005f8da13f42943881c655f
+ 25 | 8e296a067a37563370ded05f5a3bf3ec
+ 10 | d3d9446802a44259755d38e6d163e820
+ 11 | 6512bd43d9caa6e02c990b0a82652dca
+ 12 | c20ad4d76fe97759aa27a0c99bff6710
+ 13 | c51ce410c124a10e0db5e4b97fc2af39
+ 14 | aab3238922bcc25a6f606eb525ffdc56
+(10 rows)
+
+TRUNCATE tru_ftable;			-- truncate both of parent and child
+SELECT * FROM tru_ftable;
+ id | x 
+----+---
+(0 rows)
+
 -- ===================================================================
 -- test IMPORT FOREIGN SCHEMA
 -- ===================================================================
@@ -8898,7 +9131,7 @@ DO $d$
     END;
 $d$;
 ERROR:  invalid option "password"
-HINT:  Valid options in this context are: service, passfile, channel_binding, connect_timeout, dbname, host, hostaddr, port, options, application_name, keepalives, keepalives_idle, keepalives_interval, keepalives_count, tcp_user_timeout, sslmode, sslcompression, sslcert, sslkey, sslrootcert, sslcrl, requirepeer, sslminprotocolversion, sslmaxprotocolversion, gssencmode, krbsrvname, gsslib, target_session_attrs, use_remote_estimate, fdw_startup_cost, fdw_tuple_cost, extensions, updatable, fetch_size
+HINT:  Valid options in this context are: service, passfile, channel_binding, connect_timeout, dbname, host, hostaddr, port, options, application_name, keepalives, keepalives_idle, keepalives_interval, keepalives_count, tcp_user_timeout, sslmode, sslcompression, sslcert, sslkey, sslrootcert, sslcrl, requirepeer, sslminprotocolversion, sslmaxprotocolversion, gssencmode, krbsrvname, gsslib, target_session_attrs, use_remote_estimate, fdw_startup_cost, fdw_tuple_cost, extensions, updatable, truncatable, fetch_size
 CONTEXT:  SQL statement "ALTER SERVER loopback_nopw OPTIONS (ADD password 'dummypw')"
 PL/pgSQL function inline_code_block line 3 at EXECUTE
 -- If we add a password for our user mapping instead, we should get a different
diff --git a/contrib/postgres_fdw/option.c b/contrib/postgres_fdw/option.c
index c442af5bb9..843c3e0e7f 100644
--- a/contrib/postgres_fdw/option.c
+++ b/contrib/postgres_fdw/option.c
@@ -107,7 +107,8 @@ postgres_fdw_validator(PG_FUNCTION_ARGS)
 		 * Validate option value, when we can do so without any context.
 		 */
 		if (strcmp(def->defname, "use_remote_estimate") == 0 ||
-			strcmp(def->defname, "updatable") == 0)
+			strcmp(def->defname, "updatable") == 0 ||
+			strcmp(def->defname, "truncatable") == 0)
 		{
 			/* these accept only boolean values */
 			(void) defGetBoolean(def);
@@ -200,6 +201,9 @@ InitPgFdwOptions(void)
 		/* updatable is available on both server and table */
 		{"updatable", ForeignServerRelationId, false},
 		{"updatable", ForeignTableRelationId, false},
+		/* truncatable is available on both server and table */
+		{"truncatable", ForeignServerRelationId, false},
+		{"truncatable", ForeignTableRelationId, false},
 		/* fetch_size is available on both server and table */
 		{"fetch_size", ForeignServerRelationId, false},
 		{"fetch_size", ForeignTableRelationId, false},
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index 2175dff824..4d25093f33 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -373,6 +373,10 @@ static void postgresExplainForeignModify(ModifyTableState *mtstate,
 										 ExplainState *es);
 static void postgresExplainDirectModify(ForeignScanState *node,
 										ExplainState *es);
+static void postgresExecForeignTruncate(List *frels_list,
+										List *frels_extra,
+										DropBehavior behavior,
+										bool restart_seqs);
 static bool postgresAnalyzeForeignTable(Relation relation,
 										AcquireSampleRowsFunc *func,
 										BlockNumber *totalpages);
@@ -546,6 +550,9 @@ postgres_fdw_handler(PG_FUNCTION_ARGS)
 	routine->ExplainForeignModify = postgresExplainForeignModify;
 	routine->ExplainDirectModify = postgresExplainDirectModify;
 
+	/* Support function for TRUNCATE */
+	routine->ExecForeignTruncate = postgresExecForeignTruncate;
+
 	/* Support functions for ANALYZE */
 	routine->AnalyzeForeignTable = postgresAnalyzeForeignTable;
 
@@ -2656,6 +2663,84 @@ postgresExplainDirectModify(ForeignScanState *node, ExplainState *es)
 	}
 }
 
+/*
+ * postgresExecForeignTruncate
+ *		It propagates TRUNCATE command to the remote host inside of the
+ *		transaction block.
+ */
+static void
+postgresExecForeignTruncate(List *frels_list,
+							List *frels_extra,
+							DropBehavior behavior,
+							bool restart_seqs)
+{
+	Oid				server_id = InvalidOid;
+	ForeignServer  *serv = NULL;
+	UserMapping	   *user = NULL;
+	PGconn		   *conn = NULL;
+	PGresult	   *res;
+	StringInfoData	sql;
+	ListCell	   *lc;
+	bool			server_truncatable = true;
+
+	/* pick up remote connection, and sanity checks */
+	foreach (lc, frels_list)
+	{
+		Relation	frel = lfirst(lc);
+		Oid			frel_oid = RelationGetRelid(frel);
+		ForeignTable *ft = GetForeignTable(frel_oid);
+		ListCell   *cell;
+		bool		truncatable;
+
+		if (!OidIsValid(server_id))
+		{
+			server_id = GetForeignServerIdByRelId(frel_oid);
+			serv = GetForeignServer(server_id);
+			user = GetUserMapping(GetUserId(), server_id);
+			conn = GetConnection(user, false);
+			
+			foreach (cell, serv->options)
+			{
+				DefElem	   *defel = (DefElem *) lfirst(cell);
+
+				if (strcmp(defel->defname, "truncatable") == 0)
+					server_truncatable = defGetBoolean(defel);
+			}
+		}
+		else
+		{
+			/* ExecForeignTruncate() is invoked for each server */
+			Assert(server_id == GetForeignServerIdByRelId(frel_oid));
+		}
+
+		/* ensure the target foreign table is truncatable */
+		truncatable = server_truncatable;
+		foreach (cell, ft->options)
+		{
+			DefElem	   *defel = (DefElem *) lfirst(cell);
+
+			if (strcmp(defel->defname, "truncatable") == 0)
+				truncatable = defGetBoolean(defel);
+		}
+		if (!truncatable)
+			ereport(ERROR,
+					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+					 errmsg("truncate on \"%s\" is prohibited",
+							RelationGetRelationName(frel))));
+	}
+	/* set up remote query */
+	initStringInfo(&sql);
+	deparseTruncateSql(&sql, frels_list, frels_extra, behavior, restart_seqs);
+	/* run remote query */
+	if (!PQsendQuery(conn, sql.data))
+		pgfdw_report_error(ERROR, NULL, conn, false, sql.data);
+	res = pgfdw_get_result(conn, sql.data);
+	if (PQresultStatus(res) != PGRES_COMMAND_OK)
+		pgfdw_report_error(ERROR, res, conn, true, sql.data);
+	/* clean-up */
+	PQclear(res);
+	pfree(sql.data);
+}
 
 /*
  * estimate_path_cost_size
diff --git a/contrib/postgres_fdw/postgres_fdw.h b/contrib/postgres_fdw/postgres_fdw.h
index eef410db39..8d608c18db 100644
--- a/contrib/postgres_fdw/postgres_fdw.h
+++ b/contrib/postgres_fdw/postgres_fdw.h
@@ -190,6 +190,11 @@ extern void deparseDirectDeleteSql(StringInfo buf, PlannerInfo *root,
 extern void deparseAnalyzeSizeSql(StringInfo buf, Relation rel);
 extern void deparseAnalyzeSql(StringInfo buf, Relation rel,
 							  List **retrieved_attrs);
+extern void deparseTruncateSql(StringInfo buf,
+							   List *frels_list,
+							   List *frels_extra,
+							   DropBehavior behavior,
+							   bool restart_seqs);
 extern void deparseStringLiteral(StringInfo buf, const char *val);
 extern Expr *find_em_expr_for_rel(EquivalenceClass *ec, RelOptInfo *rel);
 extern Expr *find_em_expr_for_input_target(PlannerInfo *root,
diff --git a/contrib/postgres_fdw/sql/postgres_fdw.sql b/contrib/postgres_fdw/sql/postgres_fdw.sql
index 83971665e3..54bcab555f 100644
--- a/contrib/postgres_fdw/sql/postgres_fdw.sql
+++ b/contrib/postgres_fdw/sql/postgres_fdw.sql
@@ -2307,6 +2307,96 @@ select * from rem3;
 drop foreign table rem3;
 drop table loc3;
 
+-- ===================================================================
+-- test for TRUNCATE
+-- ===================================================================
+CREATE TABLE tru_rtable0 (id int primary key, x text);
+CREATE TABLE tru_rtable1 (id int primary key, y text);
+CREATE FOREIGN TABLE tru_ftable (id int, x text)
+       SERVER loopback OPTIONS (table_name 'tru_rtable0');
+INSERT INTO tru_rtable0 (SELECT x,md5(x::text) FROM generate_series(1,10) x);
+
+CREATE TABLE tru_ptable (id int, y text) PARTITION BY HASH(id);
+CREATE TABLE tru_ptable__p0 PARTITION OF tru_ptable
+                            FOR VALUES WITH (MODULUS 2, REMAINDER 0);
+CREATE FOREIGN TABLE tru_ftable__p1 PARTITION OF tru_ptable
+                                    FOR VALUES WITH (MODULUS 2, REMAINDER 1)
+       SERVER loopback OPTIONS (table_name 'tru_rtable1');
+INSERT INTO tru_ptable (SELECT x,md5(x::text) FROM generate_series(11,20) x);
+
+CREATE TABLE tru_pk_table(id int primary key, z text);
+CREATE TABLE tru_fk_table(fkey int references tru_pk_table(id));
+INSERT INTO tru_pk_table (SELECT x,md5((x+1)::text) FROM generate_series(1,10) x);
+INSERT INTO tru_fk_table (SELECT x % 10 + 1 FROM generate_series(5,25) x);
+CREATE FOREIGN TABLE tru_pk_ftable (id int, z text)
+       SERVER loopback OPTIONS (table_name 'tru_pk_table');
+
+CREATE TABLE tru_rtable_parent (id int, a text);
+CREATE TABLE tru_rtable_child (id int, a text);
+CREATE FOREIGN TABLE tru_ftable_parent (id int, a text)
+       SERVER loopback OPTIONS (table_name 'tru_rtable_parent');
+CREATE FOREIGN TABLE tru_ftable_child () INHERITS (tru_ftable_parent)
+       SERVER loopback OPTIONS (table_name 'tru_rtable_child');
+INSERT INTO tru_rtable_parent (SELECT x, md5(x::text) FROM generate_series(1,8) x);
+INSERT INTO tru_rtable_child  (SELECT x, md5(x::text) FROM generate_series(10, 18) x);
+
+-- normal truncate
+SELECT * FROM tru_ftable;
+TRUNCATE tru_ftable;
+SELECT * FROM tru_rtable0;		-- empty
+SELECT * FROM tru_ftable;		-- empty
+
+-- 'truncatable' option
+ALTER SERVER loopback OPTIONS (ADD truncatable 'false');
+TRUNCATE tru_ftable;			-- error
+ALTER SERVER loopback OPTIONS (DROP truncatable);
+ALTER FOREIGN TABLE tru_ftable OPTIONS (ADD truncatable 'false');
+TRUNCATE tru_ftable;			-- error
+ALTER FOREIGN TABLE tru_ftable OPTIONS (SET truncatable 'true');
+TRUNCATE tru_ftable;			-- accepted
+
+-- partition table mixtured by table and foreign table
+SELECT * FROM tru_ptable;
+TRUNCATE tru_ptable;
+SELECT * FROM tru_ptable;		-- empty
+SELECT * FROM tru_ptable__p0;	-- empty
+SELECT * FROM tru_ftable__p1;	-- empty
+SELECT * FROM tru_rtable1;		-- empty
+
+-- 'CASCADE' option
+SELECT * FROM tru_pk_ftable;
+TRUNCATE tru_pk_ftable;	-- failed by FK reference
+TRUNCATE tru_pk_ftable CASCADE;
+SELECT * FROM tru_pk_ftable;
+SELECT * FROM tru_fk_table;		-- also truncated
+
+-- truncate two tables at a command
+INSERT INTO tru_ftable (SELECT x,md5((x+2)::text) FROM generate_series(1,8) x);
+INSERT INTO tru_pk_ftable (SELECT x,md5((x+3)::text) FROM generate_series(3,10) x);
+SELECT * FROM tru_ftable a FULL OUTER JOIN tru_pk_ftable b ON a.id = b.id;
+TRUNCATE tru_ftable, tru_pk_ftable CASCADE;
+SELECT * FROM tru_ftable a FULL OUTER JOIN tru_pk_ftable b ON a.id = b.id;
+
+-- truncate with ONLY clause
+TRUNCATE ONLY tru_ftable_parent;
+SELECT * FROM tru_ftable_parent;
+TRUNCATE tru_ftable_parent;
+SELECT * FROM tru_ftable_parent;
+
+-- in case when remote table has inherited children
+CREATE TABLE tru_rtable0_child () INHERITS (tru_rtable0);
+INSERT INTO tru_rtable0 (SELECT x,md5(x::text) FROM generate_series(5,9) x);
+INSERT INTO tru_rtable0_child (SELECT x,md5(x::text) FROM generate_series(10,14) x);
+SELECT * FROM tru_ftable;
+
+TRUNCATE ONLY tru_ftable;		-- truncate only parent portion
+SELECT * FROM tru_ftable;
+
+INSERT INTO tru_rtable0 (SELECT x,md5(x::text) FROM generate_series(21,25) x);
+SELECT * FROM tru_ftable;
+TRUNCATE tru_ftable;			-- truncate both of parent and child
+SELECT * FROM tru_ftable;
+
 -- ===================================================================
 -- test IMPORT FOREIGN SCHEMA
 -- ===================================================================
diff --git a/doc/src/sgml/fdwhandler.sgml b/doc/src/sgml/fdwhandler.sgml
index 6587678af2..92c058277a 100644
--- a/doc/src/sgml/fdwhandler.sgml
+++ b/doc/src/sgml/fdwhandler.sgml
@@ -968,6 +968,46 @@ EndDirectModify(ForeignScanState *node);
 
    </sect2>
 
+   <sect2 id="fdw-callbacks-truncate">
+    <title>FDW Routines for Truncate</title>
+<programlisting>
+void
+ExecForeignTruncate(List *frels_list, List *frels_extra,
+                    DropBehavior behavior, bool restart_seqs);
+</programlisting>
+    <para>
+     Truncate a set of foreign tables defined by
+     <literal>frels_list</literal> belonging to the same foreign server.
+     This optional function is called during execution of
+     <command>TRUNCATE</command> for each foreign server being involved
+     in one <command>TRUNCATE</command> command (note that invocations
+     are not per foreign table).
+
+     <literal>frels_extra</literal> is same length with
+     <literal>frels_list</literal>, that delivers extra information of
+     the context where the foreign-tables are truncated.
+    </para>
+
+    <para>
+     If the <function>ExecForeignTruncate</function> pointer is set to
+     <literal>NULL</literal>, attempts to truncate the foreign table will
+     fail with an error message.
+    </para>
+    
+    <para>
+     <literal>behavior</literal> defines how foreign tables should
+     be truncated, using as possible values <literal>DROP_RESTRICT</literal>
+     and <literal>DROP_CASCADE</literal> (to map with the equivalents of
+     <command>TRUNCATE</command>).
+    </para>
+    
+    <para>
+     <literal>restart_seqs</literal> is set to <literal>true</literal>
+     if <literal>RESTART IDENTITY</literal> was supplied in the
+     <command>TRUNCATE</command>.
+    </para>
+   </sect2>
+
    <sect2 id="fdw-callbacks-row-locking">
     <title>FDW Routines for Row Locking</title>
 
diff --git a/doc/src/sgml/postgres-fdw.sgml b/doc/src/sgml/postgres-fdw.sgml
index 94992be427..887045cbdd 100644
--- a/doc/src/sgml/postgres-fdw.sgml
+++ b/doc/src/sgml/postgres-fdw.sgml
@@ -63,9 +63,10 @@
  <para>
   Now you need only <command>SELECT</command> from a foreign table to access
   the data stored in its underlying remote table.  You can also modify
-  the remote table using <command>INSERT</command>, <command>UPDATE</command>, or
-  <command>DELETE</command>.  (Of course, the remote user you have specified
-  in your user mapping must have privileges to do these things.)
+  the remote table using <command>INSERT</command>, <command>UPDATE</command>,
+  <command>DELETE</command>, or <command>TRUNCATE</command>.
+  (Of course, the remote user you have specified in your user mapping must
+  have privileges to do these things.)
  </para>
 
  <para>
@@ -392,6 +393,29 @@
      </listitem>
     </varlistentry>
 
+    <varlistentry>
+     <term><literal>truncatable</literal></term>
+     <listitem>
+      <para>
+       This option controls whether <filename>postgres_fdw</filename> allows
+       foreign tables to be truncated using <command>TRUNCATE</command>
+       command. It can be specified for a foreign table or a foreign server.
+       A table-level option overrides a server-level option.
+       The default is <literal>true</literal>.
+      </para>
+      <para>
+       Pay attention for the case when a foreign table maps remote table
+       that has inherited children or partition leafs.
+       <command>TRUNCATE</command> specifies the foreign tables with
+       <literal>ONLY</literal> clause, remove queries over the
+       <filename>postgres_fdw</filename> also specify remote tables with
+       <literal>ONLY</literal> clause, that will truncate only parent
+       portion of the remote table. In the results, it looks like
+       <command>TRUNCATE</command> command partially eliminated contents
+       of the foreign tables.
+      </para>
+     </listitem>
+    </varlistentry>
    </variablelist>
   </sect3>
 
diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index 02a7c04fdb..9762577524 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -59,6 +59,7 @@
 #include "commands/typecmds.h"
 #include "commands/user.h"
 #include "executor/executor.h"
+#include "foreign/fdwapi.h"
 #include "foreign/foreign.h"
 #include "miscadmin.h"
 #include "nodes/makefuncs.h"
@@ -295,6 +296,21 @@ struct DropRelationCallbackState
 #define		ATT_FOREIGN_TABLE		0x0020
 #define		ATT_PARTITIONED_INDEX	0x0040
 
+/*
+ * ForeignTruncateInfo
+ *
+ * Information related to truncation of foreign tables.  This is used for
+ * the elements in a hash table that uses the server OID as lookup key,
+ * and includes a per-server list of all foreign tables involved in the
+ * truncation.
+ */
+typedef struct
+{
+	Oid			server_oid;
+	List	   *frels_list;
+	List	   *frels_extra;
+} ForeignTruncateInfo;
+
 /*
  * Partition tables are expected to be dropped when the parent partitioned
  * table gets dropped. Hence for partitioning we use AUTO dependency.
@@ -1544,6 +1560,7 @@ ExecuteTruncate(TruncateStmt *stmt)
 {
 	List	   *rels = NIL;
 	List	   *relids = NIL;
+	List	   *relids_extra = NIL;
 	List	   *relids_logged = NIL;
 	ListCell   *cell;
 
@@ -1580,6 +1597,7 @@ ExecuteTruncate(TruncateStmt *stmt)
 
 		rels = lappend(rels, rel);
 		relids = lappend_oid(relids, myrelid);
+		relids_extra = lappend_int(relids_extra, (recurse ? 0 : 1));
 		/* Log this relation only if needed for logical decoding */
 		if (RelationIsLogicallyLogged(rel))
 			relids_logged = lappend_oid(relids_logged, myrelid);
@@ -1627,6 +1645,7 @@ ExecuteTruncate(TruncateStmt *stmt)
 
 				rels = lappend(rels, rel);
 				relids = lappend_oid(relids, childrelid);
+				relids_extra = lappend_int(relids_extra, -1);
 				/* Log this relation only if needed for logical decoding */
 				if (RelationIsLogicallyLogged(rel))
 					relids_logged = lappend_oid(relids_logged, childrelid);
@@ -1639,7 +1658,7 @@ ExecuteTruncate(TruncateStmt *stmt)
 					 errhint("Do not specify the ONLY keyword, or use TRUNCATE ONLY on the partitions directly.")));
 	}
 
-	ExecuteTruncateGuts(rels, relids, relids_logged,
+	ExecuteTruncateGuts(rels, relids, relids_extra, relids_logged,
 						stmt->behavior, stmt->restart_seqs);
 
 	/* And close the rels */
@@ -1665,16 +1684,21 @@ ExecuteTruncate(TruncateStmt *stmt)
  * this information handy in this form.
  */
 void
-ExecuteTruncateGuts(List *explicit_rels, List *relids, List *relids_logged,
+ExecuteTruncateGuts(List *explicit_rels,
+					List *relids,
+					List *relids_extra,
+					List *relids_logged,
 					DropBehavior behavior, bool restart_seqs)
 {
 	List	   *rels;
 	List	   *seq_relids = NIL;
+	HTAB	   *ft_htab = NULL;
 	EState	   *estate;
 	ResultRelInfo *resultRelInfos;
 	ResultRelInfo *resultRelInfo;
 	SubTransactionId mySubid;
 	ListCell   *cell;
+	ListCell   *lc1, *lc2;
 	Oid		   *logrelids;
 
 	/*
@@ -1712,6 +1736,7 @@ ExecuteTruncateGuts(List *explicit_rels, List *relids, List *relids_logged,
 				truncate_check_activity(rel);
 				rels = lappend(rels, rel);
 				relids = lappend_oid(relids, relid);
+				relids_extra = lappend_int(relids_extra, -1);
 				/* Log this relation only if needed for logical decoding */
 				if (RelationIsLogicallyLogged(rel))
 					relids_logged = lappend_oid(relids_logged, relid);
@@ -1808,14 +1833,68 @@ ExecuteTruncateGuts(List *explicit_rels, List *relids, List *relids_logged,
 	 */
 	mySubid = GetCurrentSubTransactionId();
 
-	foreach(cell, rels)
+	Assert(list_length(rels) == list_length(relids_extra));
+	forboth (lc1, rels,
+			 lc2, relids_extra)
 	{
-		Relation	rel = (Relation) lfirst(cell);
+		Relation	rel = (Relation) lfirst(lc1);
+		int			extra = lfirst_int(lc2);
 
 		/* Skip partitioned tables as there is nothing to do */
 		if (rel->rd_rel->relkind == RELKIND_PARTITIONED_TABLE)
 			continue;
 
+		/*
+		 * If truncating a foreign table, the foreign data wrapper callback
+		 * for TRUNCATE is called once for each server with a list of all the
+		 * relations to process linked to this server.  The list of relations
+		 * for each server is saved as a single entry in a hash table that
+		 * uses the server OID as lookup key.  Once the full set of lists is
+		 * built, all the entries of the hash table are scanned, and the list
+		 * of relations associated to the server is passed down to the
+		 * TRUNCATE callback of its foreign data wrapper.
+		 */
+		if (rel->rd_rel->relkind == RELKIND_FOREIGN_TABLE)
+		{
+			Oid			frel_oid = RelationGetRelid(rel);
+			Oid			server_oid = GetForeignServerIdByRelId(frel_oid);
+			bool		found;
+			ForeignTruncateInfo *ft_info;
+
+			/* if the hash table does not exist yet, initialize it */
+			if (!ft_htab)
+			{
+				HASHCTL		hctl;
+
+				memset(&hctl, 0, sizeof(HASHCTL));
+				hctl.keysize = sizeof(Oid);
+				hctl.entrysize = sizeof(ForeignTruncateInfo);
+				hctl.hcxt = CurrentMemoryContext;
+
+				ft_htab = hash_create("TRUNCATE for Foreign Tables",
+									  32,	/* start small and extend */
+									  &hctl,
+									  HASH_ELEM | HASH_BLOBS | HASH_CONTEXT);
+			}
+
+			/*
+			 * Look after the entry of the server in the hash table, and
+			 * initialize it if the entry does not exist yet.
+			 */
+			ft_info = hash_search(ft_htab, &server_oid, HASH_ENTER, &found);
+			if (!found)
+			{
+				ft_info->server_oid = server_oid;
+				ft_info->frels_list = NIL;
+				ft_info->frels_extra = NIL;
+			}
+
+			/* save the relation in the list */
+			ft_info->frels_list = lappend(ft_info->frels_list, rel);
+			ft_info->frels_extra = lappend_int(ft_info->frels_extra, extra);
+			continue;
+		}
+
 		/*
 		 * Normally, we need a transaction-safe truncation here.  However, if
 		 * the table was either created in the current (sub)transaction or has
@@ -1876,6 +1955,31 @@ ExecuteTruncateGuts(List *explicit_rels, List *relids, List *relids_logged,
 		pgstat_count_truncate(rel);
 	}
 
+	/*
+	 * Now go through the hash table, and process each entry associated to the
+	 * servers involved in the TRUNCATE.
+	 */
+	if (ft_htab)
+	{
+		ForeignTruncateInfo *ft_info;
+		HASH_SEQ_STATUS seq;
+
+		hash_seq_init(&seq, ft_htab);
+
+		while ((ft_info = hash_seq_search(&seq)) != NULL)
+		{
+			FdwRoutine *routine = GetFdwRoutineByServerId(ft_info->server_oid);
+
+			/* truncate_check_rel() has checked that already */
+			Assert(routine->ExecForeignTruncate != NULL);
+
+			routine->ExecForeignTruncate(ft_info->frels_list,
+										 ft_info->frels_extra,
+										 behavior,
+										 restart_seqs);
+		}
+	}
+
 	/*
 	 * Restart owned sequences if we were asked to.
 	 */
@@ -1962,12 +2066,24 @@ truncate_check_rel(Oid relid, Form_pg_class reltuple)
 	char	   *relname = NameStr(reltuple->relname);
 
 	/*
-	 * Only allow truncate on regular tables and partitioned tables (although,
-	 * the latter are only being included here for the following checks; no
-	 * physical truncation will occur in their case.)
+	 * Only allow truncate on regular tables, foreign tables using foreign
+	 * data wrappers supporting TRUNCATE and partitioned tables (although, the
+	 * latter are only being included here for the following checks; no
+	 * physical truncation will occur in their case.).
 	 */
-	if (reltuple->relkind != RELKIND_RELATION &&
-		reltuple->relkind != RELKIND_PARTITIONED_TABLE)
+	if (reltuple->relkind == RELKIND_FOREIGN_TABLE)
+	{
+		Oid			server_id = GetForeignServerIdByRelId(relid);
+		FdwRoutine *fdwroutine = GetFdwRoutineByServerId(server_id);
+
+		if (!fdwroutine->ExecForeignTruncate)
+			ereport(ERROR,
+					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+					 errmsg("cannot truncate foreign table \"%s\"",
+							relname)));
+	}
+	else if (reltuple->relkind != RELKIND_RELATION &&
+			 reltuple->relkind != RELKIND_PARTITIONED_TABLE)
 		ereport(ERROR,
 				(errcode(ERRCODE_WRONG_OBJECT_TYPE),
 				 errmsg("\"%s\" is not a table", relname)));
diff --git a/src/backend/replication/logical/worker.c b/src/backend/replication/logical/worker.c
index ad4a732fd2..a27930c7c6 100644
--- a/src/backend/replication/logical/worker.c
+++ b/src/backend/replication/logical/worker.c
@@ -929,6 +929,7 @@ apply_handle_truncate(StringInfo s)
 	List	   *remote_rels = NIL;
 	List	   *rels = NIL;
 	List	   *relids = NIL;
+	List	   *relids_extra = NIL;
 	List	   *relids_logged = NIL;
 	ListCell   *lc;
 
@@ -955,6 +956,7 @@ apply_handle_truncate(StringInfo s)
 		remote_rels = lappend(remote_rels, rel);
 		rels = lappend(rels, rel->localrel);
 		relids = lappend_oid(relids, rel->localreloid);
+		relids_extra = lappend_int(relids_extra, 0);
 		if (RelationIsLogicallyLogged(rel->localrel))
 			relids_logged = lappend_oid(relids_logged, rel->localreloid);
 	}
@@ -964,8 +966,12 @@ apply_handle_truncate(StringInfo s)
 	 * replaying changes without further cascading. This might be later
 	 * changeable with a user specified option.
 	 */
-	ExecuteTruncateGuts(rels, relids, relids_logged, DROP_RESTRICT, restart_seqs);
-
+	ExecuteTruncateGuts(rels,
+						relids,
+						relids_extra,
+						relids_logged,
+						DROP_RESTRICT,
+						restart_seqs);
 	foreach(lc, remote_rels)
 	{
 		LogicalRepRelMapEntry *rel = lfirst(lc);
diff --git a/src/include/commands/tablecmds.h b/src/include/commands/tablecmds.h
index c1581ad178..7c3ebe4353 100644
--- a/src/include/commands/tablecmds.h
+++ b/src/include/commands/tablecmds.h
@@ -56,8 +56,12 @@ extern void AlterRelationNamespaceInternal(Relation classRel, Oid relOid,
 extern void CheckTableNotInUse(Relation rel, const char *stmt);
 
 extern void ExecuteTruncate(TruncateStmt *stmt);
-extern void ExecuteTruncateGuts(List *explicit_rels, List *relids, List *relids_logged,
-								DropBehavior behavior, bool restart_seqs);
+extern void ExecuteTruncateGuts(List *explicit_rels,
+								List *relids,
+								List *relids_extra,
+								List *relids_logged,
+								DropBehavior behavior,
+								bool restart_seqs);
 
 extern void SetRelationHasSubclass(Oid relationId, bool relhassubclass);
 
diff --git a/src/include/foreign/fdwapi.h b/src/include/foreign/fdwapi.h
index 95556dfb15..674ed449bb 100644
--- a/src/include/foreign/fdwapi.h
+++ b/src/include/foreign/fdwapi.h
@@ -151,6 +151,11 @@ typedef bool (*AnalyzeForeignTable_function) (Relation relation,
 typedef List *(*ImportForeignSchema_function) (ImportForeignSchemaStmt *stmt,
 											   Oid serverOid);
 
+typedef void (*ExecForeignTruncate_function) (List *frels_list,
+											  List *frels_extra,
+											  DropBehavior behavior,
+											  bool restart_seqs);
+
 typedef Size (*EstimateDSMForeignScan_function) (ForeignScanState *node,
 												 ParallelContext *pcxt);
 typedef void (*InitializeDSMForeignScan_function) (ForeignScanState *node,
@@ -236,6 +241,9 @@ typedef struct FdwRoutine
 	/* Support functions for IMPORT FOREIGN SCHEMA */
 	ImportForeignSchema_function ImportForeignSchema;
 
+	/* Support functions for TRUNCATE */
+	ExecForeignTruncate_function ExecForeignTruncate;
+
 	/* Support functions for parallelism under Gather node */
 	IsForeignScanParallelSafe_function IsForeignScanParallelSafe;
 	EstimateDSMForeignScan_function EstimateDSMForeignScan;
diff --git a/src/test/regress/expected/foreign_data.out b/src/test/regress/expected/foreign_data.out
index b9e25820bc..e2c0bcea51 100644
--- a/src/test/regress/expected/foreign_data.out
+++ b/src/test/regress/expected/foreign_data.out
@@ -1807,9 +1807,9 @@ Inherits: fd_pt1
 
 -- TRUNCATE doesn't work on foreign tables, either directly or recursively
 TRUNCATE ft2;  -- ERROR
-ERROR:  "ft2" is not a table
+ERROR:  foreign-data wrapper "dummy" has no handler
 TRUNCATE fd_pt1;  -- ERROR
-ERROR:  "ft2" is not a table
+ERROR:  foreign-data wrapper "dummy" has no handler
 DROP TABLE fd_pt1 CASCADE;
 NOTICE:  drop cascades to foreign table ft2
 -- IMPORT FOREIGN SCHEMA
@@ -2032,9 +2032,9 @@ ALTER FOREIGN TABLE fd_pt2_1 ADD CONSTRAINT fd_pt2chk1 CHECK (c1 > 0);
 ALTER TABLE fd_pt2 ATTACH PARTITION fd_pt2_1 FOR VALUES IN (1);
 -- TRUNCATE doesn't work on foreign tables, either directly or recursively
 TRUNCATE fd_pt2_1;  -- ERROR
-ERROR:  "fd_pt2_1" is not a table
+ERROR:  foreign-data wrapper "dummy" has no handler
 TRUNCATE fd_pt2;  -- ERROR
-ERROR:  "fd_pt2_1" is not a table
+ERROR:  foreign-data wrapper "dummy" has no handler
 DROP FOREIGN TABLE fd_pt2_1;
 DROP TABLE fd_pt2;
 -- foreign table cannot be part of partition tree made of temporary
diff --git a/src/tools/pgindent/typedefs.list b/src/tools/pgindent/typedefs.list
index e216de9570..ef2bd90db1 100644
--- a/src/tools/pgindent/typedefs.list
+++ b/src/tools/pgindent/typedefs.list
@@ -686,6 +686,7 @@ ForeignScanState
 ForeignServer
 ForeignServerInfo
 ForeignTable
+ForeignTruncateInfo
 ForkNumber
 FormData_pg_aggregate
 FormData_pg_am