Available disk space per tablespace

Started by Christoph Berg10 months ago10 messages

myon@debian.org

10 months ago

1 attachment(s)

Hi,

I'm picking up a 5 year old patch again:
/messages/by-id/20191108132419.GG8017@msg.df7cb.de

Users will be interested in knowing how much extra data they can load
into a database, but PG currently does not expose that number. This
patch introduces a new function pg_tablespace_avail() that takes a
tablespace name or oid, and returns the number of bytes "available"
there. This is the number without any reserved blocks (Unix, f_avail)
or available to the current user (Windows).

(This is not meant to replace a full-fledged OS monitoring system that
has much more numbers about disks and everything, it is filling a UX
gap.)

Compared to the last patch, this just returns a single number so it's
easier to use - total space isn't all that interesting, we just return
the number the user wants.

The free space is included in \db+ output:

postgres =# \db+
List of tablespaces
Name │ Owner │ Location │ Access privileges │ Options │ Size │ Free │ Description
────────────┼───────┼──────────┼───────────────────┼─────────┼─────────┼────────┼─────────────
pg_default │ myon │ │ ∅ │ ∅ │ 23 MB │ 538 GB │ ∅
pg_global │ myon │ │ ∅ │ ∅ │ 556 kB │ 538 GB │ ∅
spc │ myon │ /tmp/spc │ ∅ │ ∅ │ 0 bytes │ 31 GB │ ∅
(3 rows)

The patch has also been tested on Windows.

TODO: Figure out which systems need statfs() vs statvfs()

Christoph

Attachments:

0001-Add-pg_tablespace_avail-functions.patchtext/x-diff; charset=us-asciiDownload

From 455640e375e7142d4bef2e4f47f678e3712a5a27 Mon Sep 17 00:00:00 2001
From: Christoph Berg <myon@debian.org>
Date: Fri, 8 Nov 2019 14:12:35 +0100
Subject: [PATCH] Add pg_tablespace_avail() functions

This exposes the f_avail value from statvfs() on tablespace directories
on the SQL level, allowing monitoring of free disk space from within the
server. On windows, GetDiskFreeSpaceEx() is used.

Permissions required match those from pg_tablespace_size.

In psql, include a new "Free" column in \db+ output.
---
 doc/src/sgml/func.sgml          | 21 ++++++++
 doc/src/sgml/ref/psql-ref.sgml  |  2 +-
 src/backend/utils/adt/dbsize.c  | 94 +++++++++++++++++++++++++++++++++
 src/bin/psql/describe.c         | 11 ++--
 src/include/catalog/pg_proc.dat |  8 +++
 5 files changed, 132 insertions(+), 4 deletions(-)

diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml
index 51dd8ad6571..0b4456ad958 100644
--- a/doc/src/sgml/func.sgml
+++ b/doc/src/sgml/func.sgml
@@ -30093,6 +30093,27 @@ postgres=# SELECT '0/0'::pg_lsn + pd.segment_number * ps.setting::int + :offset
        </para></entry>
       </row>
 
+      <row>
+       <entry role="func_table_entry"><para role="func_signature">
+        <indexterm>
+         <primary>pg_tablespace_avail</primary>
+        </indexterm>
+        <function>pg_tablespace_avail</function> ( <type>name</type> )
+        <returnvalue>bigint</returnvalue>
+       </para>
+       <para role="func_signature">
+        <function>pg_tablespace_avail</function> ( <type>oid</type> )
+        <returnvalue>bigint</returnvalue>
+       </para>
+       <para>
+        Returns the available disk space in the tablespace with the
+        specified name or OID. To use this function, you must
+        have <literal>CREATE</literal> privilege on the specified tablespace
+        or have privileges of the <literal>pg_read_all_stats</literal> role,
+        unless it is the default tablespace for the current database.
+       </para></entry>
+      </row>
+
       <row>
        <entry role="func_table_entry"><para role="func_signature">
         <indexterm>
diff --git a/doc/src/sgml/ref/psql-ref.sgml b/doc/src/sgml/ref/psql-ref.sgml
index cedccc14129..9e1bec0b422 100644
--- a/doc/src/sgml/ref/psql-ref.sgml
+++ b/doc/src/sgml/ref/psql-ref.sgml
@@ -1492,7 +1492,7 @@ SELECT $1 \parse stmt1
         If <literal>x</literal> is appended to the command name, the results
         are displayed in expanded mode.
         If <literal>+</literal> is appended to the command name, each tablespace
-        is listed with its associated options, on-disk size, permissions and
+        is listed with its associated options, on-disk size and free disk space, permissions and
         description.
         </para>
         </listitem>
diff --git a/src/backend/utils/adt/dbsize.c b/src/backend/utils/adt/dbsize.c
index 25865b660ef..3a2f47c50ec 100644
--- a/src/backend/utils/adt/dbsize.c
+++ b/src/backend/utils/adt/dbsize.c
@@ -12,6 +12,11 @@
 #include "postgres.h"
 
 #include <sys/stat.h>
+#ifdef WIN32
+#include <fileapi.h>
+#else
+#include <sys/statvfs.h>
+#endif
 
 #include "access/htup_details.h"
 #include "access/relation.h"
@@ -316,6 +321,95 @@ pg_tablespace_size_name(PG_FUNCTION_ARGS)
 }
 
 
+/*
+ * Return available disk space of tablespace. Returns -1 if the tablespace
+ * directory cannot be found.
+ */
+static int64
+calculate_tablespace_avail(Oid tblspcOid)
+{
+	char		tblspcPath[MAXPGPATH];
+	AclResult	aclresult;
+#ifdef WIN32
+	ULARGE_INTEGER lpFreeBytesAvailable;
+#else
+	struct statvfs fst;
+#endif
+
+	/*
+	 * User must have privileges of pg_read_all_stats or have CREATE privilege
+	 * for target tablespace, either explicitly granted or implicitly because
+	 * it is default for current database.
+	 */
+	if (tblspcOid != MyDatabaseTableSpace &&
+		!has_privs_of_role(GetUserId(), ROLE_PG_READ_ALL_STATS))
+	{
+		aclresult = object_aclcheck(TableSpaceRelationId, tblspcOid, GetUserId(), ACL_CREATE);
+		if (aclresult != ACLCHECK_OK)
+			aclcheck_error(aclresult, OBJECT_TABLESPACE,
+						   get_tablespace_name(tblspcOid));
+	}
+
+	if (tblspcOid == DEFAULTTABLESPACE_OID)
+		snprintf(tblspcPath, MAXPGPATH, "base");
+	else if (tblspcOid == GLOBALTABLESPACE_OID)
+		snprintf(tblspcPath, MAXPGPATH, "global");
+	else
+		snprintf(tblspcPath, MAXPGPATH, "%s/%u/%s", PG_TBLSPC_DIR, tblspcOid,
+				 TABLESPACE_VERSION_DIRECTORY);
+
+#ifdef WIN32
+	if (GetDiskFreeSpaceEx(tblspcPath, &lpFreeBytesAvailable, NULL, NULL) == false)
+		return -1;
+
+	return lpFreeBytesAvailable.QuadPart; /* ULONGLONG part of ULARGE_INTEGER */
+#else
+	if (statvfs(tblspcPath, &fst) < 0)
+		return -1;
+
+	return fst.f_bavail * fst.f_bsize; /* available blocks times block size */
+#endif
+}
+
+Datum
+pg_tablespace_avail_oid(PG_FUNCTION_ARGS)
+{
+	Oid			tblspcOid = PG_GETARG_OID(0);
+	int64		avail;
+
+	/*
+	 * Not needed for correctness, but avoid non-user-facing error message
+	 * later if the tablespace doesn't exist.
+	 */
+	if (!SearchSysCacheExists1(TABLESPACEOID, ObjectIdGetDatum(tblspcOid)))
+		ereport(ERROR,
+				errcode(ERRCODE_UNDEFINED_OBJECT),
+				errmsg("tablespace with OID %u does not exist", tblspcOid));
+
+	avail = calculate_tablespace_avail(tblspcOid);
+
+	if (avail < 0)
+		PG_RETURN_NULL();
+
+	PG_RETURN_INT64(avail);
+}
+
+Datum
+pg_tablespace_avail_name(PG_FUNCTION_ARGS)
+{
+	Name		tblspcName = PG_GETARG_NAME(0);
+	Oid			tblspcOid = get_tablespace_oid(NameStr(*tblspcName), false);
+	int64		avail;
+
+	avail = calculate_tablespace_avail(tblspcOid);
+
+	if (avail < 0)
+		PG_RETURN_NULL();
+
+	PG_RETURN_INT64(avail);
+}
+
+
 /*
  * calculate size of (one fork of) a relation
  *
diff --git a/src/bin/psql/describe.c b/src/bin/psql/describe.c
index e6cf468ac9e..8c52a126ac1 100644
--- a/src/bin/psql/describe.c
+++ b/src/bin/psql/describe.c
@@ -241,10 +241,15 @@ describeTablespaces(const char *pattern, bool verbose)
 		printACLColumn(&buf, "spcacl");
 		appendPQExpBuffer(&buf,
 						  ",\n  spcoptions AS \"%s\""
-						  ",\n  pg_catalog.pg_size_pretty(pg_catalog.pg_tablespace_size(oid)) AS \"%s\""
-						  ",\n  pg_catalog.shobj_description(oid, 'pg_tablespace') AS \"%s\"",
+						  ",\n  pg_catalog.pg_size_pretty(pg_catalog.pg_tablespace_size(oid)) AS \"%s\"",
 						  gettext_noop("Options"),
-						  gettext_noop("Size"),
+						  gettext_noop("Size"));
+		if (pset.sversion >= 180000)
+			appendPQExpBuffer(&buf,
+							  ",\n  pg_catalog.pg_size_pretty(pg_catalog.pg_tablespace_avail(oid)) AS \"%s\"",
+							  gettext_noop("Free"));
+		appendPQExpBuffer(&buf,
+						  ",\n  pg_catalog.shobj_description(oid, 'pg_tablespace') AS \"%s\"",
 						  gettext_noop("Description"));
 	}
 
diff --git a/src/include/catalog/pg_proc.dat b/src/include/catalog/pg_proc.dat
index 42e427f8fe8..9d64da6bfb8 100644
--- a/src/include/catalog/pg_proc.dat
+++ b/src/include/catalog/pg_proc.dat
@@ -7680,6 +7680,14 @@
   descr => 'total disk space usage for the specified tablespace',
   proname => 'pg_tablespace_size', provolatile => 'v', prorettype => 'int8',
   proargtypes => 'name', prosrc => 'pg_tablespace_size_name' },
+{ oid => '6015',
+  descr => 'disk stats for the specified tablespace',
+  proname => 'pg_tablespace_avail', provolatile => 'v', prorettype => 'int8',
+  proargtypes => 'oid', prosrc => 'pg_tablespace_avail_oid' },
+{ oid => '6016',
+  descr => 'disk stats for the specified tablespace',
+  proname => 'pg_tablespace_avail', provolatile => 'v', prorettype => 'int8',
+  proargtypes => 'name', prosrc => 'pg_tablespace_avail_name' },
 { oid => '2324', descr => 'total disk space usage for the specified database',
   proname => 'pg_database_size', provolatile => 'v', prorettype => 'int8',
   proargtypes => 'oid', prosrc => 'pg_database_size_oid' },
-- 
2.47.2

Quan Zongliang

quanzongliang@yeah.net

10 months ago

In reply to: Christoph Berg (#1)

1 attachment(s)

Re: Available disk space per tablespace

On 2025/3/14 02:10, Christoph Berg wrote:

Hi,

I'm picking up a 5 year old patch again:
/messages/by-id/20191108132419.GG8017@msg.df7cb.de

Users will be interested in knowing how much extra data they can load
into a database, but PG currently does not expose that number. This
patch introduces a new function pg_tablespace_avail() that takes a
tablespace name or oid, and returns the number of bytes "available"
there. This is the number without any reserved blocks (Unix, f_avail)
or available to the current user (Windows).

(This is not meant to replace a full-fledged OS monitoring system that
has much more numbers about disks and everything, it is filling a UX
gap.)

Compared to the last patch, this just returns a single number so it's
easier to use - total space isn't all that interesting, we just return
the number the user wants.

The free space is included in \db+ output:

postgres =# \db+
List of tablespaces
Name │ Owner │ Location │ Access privileges │ Options │ Size │ Free │ Description
────────────┼───────┼──────────┼───────────────────┼─────────┼─────────┼────────┼─────────────
pg_default │ myon │ │ ∅ │ ∅ │ 23 MB │ 538 GB │ ∅
pg_global │ myon │ │ ∅ │ ∅ │ 556 kB │ 538 GB │ ∅
spc │ myon │ /tmp/spc │ ∅ │ ∅ │ 0 bytes │ 31 GB │ ∅
(3 rows)

The patch has also been tested on Windows.

TODO: Figure out which systems need statfs() vs statvfs()

I tested the patch under macos. Abnormal work:

According to the statvfs documentation for macOS
f_frsize The size in bytes of the minimum unit of allocation on
this file system.
f_bsize The preferred length of I/O requests for files on this
file system.

In addition, many systems use 1000 as 1k to represent the storage size.
Shouldn't we consider this factor as well?

Show quoted text

Christoph

Attachments:

0002-Add-pg_tablespace_avail-functions.patchtext/plain; charset=UTF-8; name=0002-Add-pg_tablespace_avail-functions.patchDownload

diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml
index 1c3810e1a04..c0758b9244f 100644
--- a/doc/src/sgml/func.sgml
+++ b/doc/src/sgml/func.sgml
@@ -30089,6 +30089,27 @@ postgres=# SELECT '0/0'::pg_lsn + pd.segment_number * ps.setting::int + :offset
        </para></entry>
       </row>
 
+      <row>
+       <entry role="func_table_entry"><para role="func_signature">
+        <indexterm>
+         <primary>pg_tablespace_avail</primary>
+        </indexterm>
+        <function>pg_tablespace_avail</function> ( <type>name</type> )
+        <returnvalue>bigint</returnvalue>
+       </para>
+       <para role="func_signature">
+        <function>pg_tablespace_avail</function> ( <type>oid</type> )
+        <returnvalue>bigint</returnvalue>
+       </para>
+       <para>
+        Returns the available disk space in the tablespace with the
+        specified name or OID. To use this function, you must
+        have <literal>CREATE</literal> privilege on the specified tablespace
+        or have privileges of the <literal>pg_read_all_stats</literal> role,
+        unless it is the default tablespace for the current database.
+       </para></entry>
+      </row>
+
       <row>
        <entry role="func_table_entry"><para role="func_signature">
         <indexterm>
diff --git a/doc/src/sgml/ref/psql-ref.sgml b/doc/src/sgml/ref/psql-ref.sgml
index cedccc14129..9e1bec0b422 100644
--- a/doc/src/sgml/ref/psql-ref.sgml
+++ b/doc/src/sgml/ref/psql-ref.sgml
@@ -1492,7 +1492,7 @@ SELECT $1 \parse stmt1
         If <literal>x</literal> is appended to the command name, the results
         are displayed in expanded mode.
         If <literal>+</literal> is appended to the command name, each tablespace
-        is listed with its associated options, on-disk size, permissions and
+        is listed with its associated options, on-disk size and free disk space, permissions and
         description.
         </para>
         </listitem>
diff --git a/src/backend/utils/adt/dbsize.c b/src/backend/utils/adt/dbsize.c
index 25865b660ef..a2637953ce0 100644
--- a/src/backend/utils/adt/dbsize.c
+++ b/src/backend/utils/adt/dbsize.c
@@ -12,6 +12,11 @@
 #include "postgres.h"
 
 #include <sys/stat.h>
+#ifdef WIN32
+#include <fileapi.h>
+#else
+#include <sys/statvfs.h>
+#endif
 
 #include "access/htup_details.h"
 #include "access/relation.h"
@@ -316,6 +321,99 @@ pg_tablespace_size_name(PG_FUNCTION_ARGS)
 }
 
 
+/*
+ * Return available disk space of tablespace. Returns -1 if the tablespace
+ * directory cannot be found.
+ */
+static int64
+calculate_tablespace_avail(Oid tblspcOid)
+{
+	char		tblspcPath[MAXPGPATH];
+	AclResult	aclresult;
+#ifdef WIN32
+	ULARGE_INTEGER lpFreeBytesAvailable;
+#else
+	struct statvfs fst;
+#endif
+
+	/*
+	 * User must have privileges of pg_read_all_stats or have CREATE privilege
+	 * for target tablespace, either explicitly granted or implicitly because
+	 * it is default for current database.
+	 */
+	if (tblspcOid != MyDatabaseTableSpace &&
+		!has_privs_of_role(GetUserId(), ROLE_PG_READ_ALL_STATS))
+	{
+		aclresult = object_aclcheck(TableSpaceRelationId, tblspcOid, GetUserId(), ACL_CREATE);
+		if (aclresult != ACLCHECK_OK)
+			aclcheck_error(aclresult, OBJECT_TABLESPACE,
+						   get_tablespace_name(tblspcOid));
+	}
+
+	if (tblspcOid == DEFAULTTABLESPACE_OID)
+		snprintf(tblspcPath, MAXPGPATH, "base");
+	else if (tblspcOid == GLOBALTABLESPACE_OID)
+		snprintf(tblspcPath, MAXPGPATH, "global");
+	else
+		snprintf(tblspcPath, MAXPGPATH, "%s/%u/%s", PG_TBLSPC_DIR, tblspcOid,
+				 TABLESPACE_VERSION_DIRECTORY);
+
+#ifdef WIN32
+	if (GetDiskFreeSpaceEx(tblspcPath, &lpFreeBytesAvailable, NULL, NULL) == false)
+		return -1;
+
+	return lpFreeBytesAvailable.QuadPart; /* ULONGLONG part of ULARGE_INTEGER */
+#else
+	if (statvfs(tblspcPath, &fst) < 0)
+		return -1;
+
+#if defined(__darwin__)
+	return fst.f_bavail * fst.f_frsize; /* available blocks times block size */
+#else
+	return fst.f_bavail * fst.f_bsize; /* available blocks times block size */
+#endif   /* __darwin__ */
+#endif
+}
+
+Datum
+pg_tablespace_avail_oid(PG_FUNCTION_ARGS)
+{
+	Oid			tblspcOid = PG_GETARG_OID(0);
+	int64		avail;
+
+	/*
+	 * Not needed for correctness, but avoid non-user-facing error message
+	 * later if the tablespace doesn't exist.
+	 */
+	if (!SearchSysCacheExists1(TABLESPACEOID, ObjectIdGetDatum(tblspcOid)))
+		ereport(ERROR,
+				errcode(ERRCODE_UNDEFINED_OBJECT),
+				errmsg("tablespace with OID %u does not exist", tblspcOid));
+
+	avail = calculate_tablespace_avail(tblspcOid);
+
+	if (avail < 0)
+		PG_RETURN_NULL();
+
+	PG_RETURN_INT64(avail);
+}
+
+Datum
+pg_tablespace_avail_name(PG_FUNCTION_ARGS)
+{
+	Name		tblspcName = PG_GETARG_NAME(0);
+	Oid			tblspcOid = get_tablespace_oid(NameStr(*tblspcName), false);
+	int64		avail;
+
+	avail = calculate_tablespace_avail(tblspcOid);
+
+	if (avail < 0)
+		PG_RETURN_NULL();
+
+	PG_RETURN_INT64(avail);
+}
+
+
 /*
  * calculate size of (one fork of) a relation
  *
diff --git a/src/bin/psql/describe.c b/src/bin/psql/describe.c
index e6cf468ac9e..8c52a126ac1 100644
--- a/src/bin/psql/describe.c
+++ b/src/bin/psql/describe.c
@@ -241,10 +241,15 @@ describeTablespaces(const char *pattern, bool verbose)
 		printACLColumn(&buf, "spcacl");
 		appendPQExpBuffer(&buf,
 						  ",\n  spcoptions AS \"%s\""
-						  ",\n  pg_catalog.pg_size_pretty(pg_catalog.pg_tablespace_size(oid)) AS \"%s\""
-						  ",\n  pg_catalog.shobj_description(oid, 'pg_tablespace') AS \"%s\"",
+						  ",\n  pg_catalog.pg_size_pretty(pg_catalog.pg_tablespace_size(oid)) AS \"%s\"",
 						  gettext_noop("Options"),
-						  gettext_noop("Size"),
+						  gettext_noop("Size"));
+		if (pset.sversion >= 180000)
+			appendPQExpBuffer(&buf,
+							  ",\n  pg_catalog.pg_size_pretty(pg_catalog.pg_tablespace_avail(oid)) AS \"%s\"",
+							  gettext_noop("Free"));
+		appendPQExpBuffer(&buf,
+						  ",\n  pg_catalog.shobj_description(oid, 'pg_tablespace') AS \"%s\"",
 						  gettext_noop("Description"));
 	}
 
diff --git a/src/include/catalog/pg_proc.dat b/src/include/catalog/pg_proc.dat
index 890822eaf79..39c3b8c2552 100644
--- a/src/include/catalog/pg_proc.dat
+++ b/src/include/catalog/pg_proc.dat
@@ -7683,6 +7683,14 @@
   descr => 'total disk space usage for the specified tablespace',
   proname => 'pg_tablespace_size', provolatile => 'v', prorettype => 'int8',
   proargtypes => 'name', prosrc => 'pg_tablespace_size_name' },
+{ oid => '6015',
+  descr => 'disk stats for the specified tablespace',
+  proname => 'pg_tablespace_avail', provolatile => 'v', prorettype => 'int8',
+  proargtypes => 'oid', prosrc => 'pg_tablespace_avail_oid' },
+{ oid => '6016',
+  descr => 'disk stats for the specified tablespace',
+  proname => 'pg_tablespace_avail', provolatile => 'v', prorettype => 'int8',
+  proargtypes => 'name', prosrc => 'pg_tablespace_avail_name' },
 { oid => '2324', descr => 'total disk space usage for the specified database',
   proname => 'pg_database_size', provolatile => 'v', prorettype => 'int8',
   proargtypes => 'oid', prosrc => 'pg_database_size_oid' },

Christoph Berg

myon@debian.org

10 months ago

In reply to: Quan Zongliang (#2)

1 attachment(s)

Re: Available disk space per tablespace

Re: Quan Zongliang

According to the statvfs documentation for macOS
f_frsize The size in bytes of the minimum unit of allocation on this
file system.
f_bsize The preferred length of I/O requests for files on this file
system.

Thanks for catching that. f_frsize is the correct field to use. The
statvfs(3) manpage on Linux has it as well, but it's less pronounced
there so I missed it:

struct statvfs {
unsigned long f_bsize; /* Filesystem block size */
unsigned long f_frsize; /* Fragment size */
fsblkcnt_t f_blocks; /* Size of fs in f_frsize units */
fsblkcnt_t f_bfree; /* Number of free blocks */
fsblkcnt_t f_bavail; /* Number of free blocks for
unprivileged users */

In addition, many systems use 1000 as 1k to represent the storage size.
Shouldn't we consider this factor as well?

That would be a different pg_size_pretty() function, unrelated to this
patch.

I'm still unconvinced if we should use statfs() instead of statvfs()
on *BSD or if their manpage is just trolling us and statvfs is just
fine.

DESCRIPTION
The statvfs() and fstatvfs() functions fill the structure pointed to by
buf with garbage. This garbage will occasionally bear resemblance to
file system statistics, but portable applications must not depend on
this.

Christoph

Attachments:

v3-0001-Add-pg_tablespace_avail-functions.patchtext/x-diff; charset=us-asciiDownload

From df4ce715ff91bf095de94ee374fff0ebe9c1d4de Mon Sep 17 00:00:00 2001
From: Christoph Berg <myon@debian.org>
Date: Fri, 14 Mar 2025 16:29:19 +0100
Subject: [PATCH] Add pg_tablespace_avail() functions

This exposes the f_avail value from statvfs() on tablespace directories
on the SQL level, allowing monitoring of free disk space from within the
server. On windows, GetDiskFreeSpaceEx() is used.

Permissions required match those from pg_tablespace_size().

In psql, include a new "Free" column in \db+ output.

Add test coverage for pg_tablespace_avail() and the previously not
covered pg_tablespace_size() function.
---
 doc/src/sgml/func.sgml                   | 21 ++++++
 doc/src/sgml/ref/psql-ref.sgml           |  2 +-
 src/backend/utils/adt/dbsize.c           | 94 ++++++++++++++++++++++++
 src/bin/psql/describe.c                  | 11 ++-
 src/include/catalog/pg_proc.dat          |  8 ++
 src/test/regress/expected/tablespace.out | 21 ++++++
 src/test/regress/sql/tablespace.sql      | 10 +++
 7 files changed, 163 insertions(+), 4 deletions(-)

diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml
index 51dd8ad6571..0b4456ad958 100644
--- a/doc/src/sgml/func.sgml
+++ b/doc/src/sgml/func.sgml
@@ -30093,6 +30093,27 @@ postgres=# SELECT '0/0'::pg_lsn + pd.segment_number * ps.setting::int + :offset
        </para></entry>
       </row>
 
+      <row>
+       <entry role="func_table_entry"><para role="func_signature">
+        <indexterm>
+         <primary>pg_tablespace_avail</primary>
+        </indexterm>
+        <function>pg_tablespace_avail</function> ( <type>name</type> )
+        <returnvalue>bigint</returnvalue>
+       </para>
+       <para role="func_signature">
+        <function>pg_tablespace_avail</function> ( <type>oid</type> )
+        <returnvalue>bigint</returnvalue>
+       </para>
+       <para>
+        Returns the available disk space in the tablespace with the
+        specified name or OID. To use this function, you must
+        have <literal>CREATE</literal> privilege on the specified tablespace
+        or have privileges of the <literal>pg_read_all_stats</literal> role,
+        unless it is the default tablespace for the current database.
+       </para></entry>
+      </row>
+
       <row>
        <entry role="func_table_entry"><para role="func_signature">
         <indexterm>
diff --git a/doc/src/sgml/ref/psql-ref.sgml b/doc/src/sgml/ref/psql-ref.sgml
index cedccc14129..9e1bec0b422 100644
--- a/doc/src/sgml/ref/psql-ref.sgml
+++ b/doc/src/sgml/ref/psql-ref.sgml
@@ -1492,7 +1492,7 @@ SELECT $1 \parse stmt1
         If <literal>x</literal> is appended to the command name, the results
         are displayed in expanded mode.
         If <literal>+</literal> is appended to the command name, each tablespace
-        is listed with its associated options, on-disk size, permissions and
+        is listed with its associated options, on-disk size and free disk space, permissions and
         description.
         </para>
         </listitem>
diff --git a/src/backend/utils/adt/dbsize.c b/src/backend/utils/adt/dbsize.c
index 25865b660ef..30e0cb8d111 100644
--- a/src/backend/utils/adt/dbsize.c
+++ b/src/backend/utils/adt/dbsize.c
@@ -12,6 +12,11 @@
 #include "postgres.h"
 
 #include <sys/stat.h>
+#ifdef WIN32
+#include <fileapi.h>
+#else
+#include <sys/statvfs.h>
+#endif
 
 #include "access/htup_details.h"
 #include "access/relation.h"
@@ -316,6 +321,95 @@ pg_tablespace_size_name(PG_FUNCTION_ARGS)
 }
 
 
+/*
+ * Return available disk space of tablespace. Returns -1 if the tablespace
+ * directory cannot be found.
+ */
+static int64
+calculate_tablespace_avail(Oid tblspcOid)
+{
+	char		tblspcPath[MAXPGPATH];
+	AclResult	aclresult;
+#ifdef WIN32
+	ULARGE_INTEGER lpFreeBytesAvailable;
+#else
+	struct statvfs fst;
+#endif
+
+	/*
+	 * User must have privileges of pg_read_all_stats or have CREATE privilege
+	 * for target tablespace, either explicitly granted or implicitly because
+	 * it is default for current database.
+	 */
+	if (tblspcOid != MyDatabaseTableSpace &&
+		!has_privs_of_role(GetUserId(), ROLE_PG_READ_ALL_STATS))
+	{
+		aclresult = object_aclcheck(TableSpaceRelationId, tblspcOid, GetUserId(), ACL_CREATE);
+		if (aclresult != ACLCHECK_OK)
+			aclcheck_error(aclresult, OBJECT_TABLESPACE,
+						   get_tablespace_name(tblspcOid));
+	}
+
+	if (tblspcOid == DEFAULTTABLESPACE_OID)
+		snprintf(tblspcPath, MAXPGPATH, "base");
+	else if (tblspcOid == GLOBALTABLESPACE_OID)
+		snprintf(tblspcPath, MAXPGPATH, "global");
+	else
+		snprintf(tblspcPath, MAXPGPATH, "%s/%u/%s", PG_TBLSPC_DIR, tblspcOid,
+				 TABLESPACE_VERSION_DIRECTORY);
+
+#ifdef WIN32
+	if (GetDiskFreeSpaceEx(tblspcPath, &lpFreeBytesAvailable, NULL, NULL) == false)
+		return -1;
+
+	return lpFreeBytesAvailable.QuadPart; /* ULONGLONG part of ULARGE_INTEGER */
+#else
+	if (statvfs(tblspcPath, &fst) < 0)
+		return -1;
+
+	return fst.f_bavail * fst.f_frsize; /* available blocks times fragment size */
+#endif
+}
+
+Datum
+pg_tablespace_avail_oid(PG_FUNCTION_ARGS)
+{
+	Oid			tblspcOid = PG_GETARG_OID(0);
+	int64		avail;
+
+	/*
+	 * Not needed for correctness, but avoid non-user-facing error message
+	 * later if the tablespace doesn't exist.
+	 */
+	if (!SearchSysCacheExists1(TABLESPACEOID, ObjectIdGetDatum(tblspcOid)))
+		ereport(ERROR,
+				errcode(ERRCODE_UNDEFINED_OBJECT),
+				errmsg("tablespace with OID %u does not exist", tblspcOid));
+
+	avail = calculate_tablespace_avail(tblspcOid);
+
+	if (avail < 0)
+		PG_RETURN_NULL();
+
+	PG_RETURN_INT64(avail);
+}
+
+Datum
+pg_tablespace_avail_name(PG_FUNCTION_ARGS)
+{
+	Name		tblspcName = PG_GETARG_NAME(0);
+	Oid			tblspcOid = get_tablespace_oid(NameStr(*tblspcName), false);
+	int64		avail;
+
+	avail = calculate_tablespace_avail(tblspcOid);
+
+	if (avail < 0)
+		PG_RETURN_NULL();
+
+	PG_RETURN_INT64(avail);
+}
+
+
 /*
  * calculate size of (one fork of) a relation
  *
diff --git a/src/bin/psql/describe.c b/src/bin/psql/describe.c
index e6cf468ac9e..8c52a126ac1 100644
--- a/src/bin/psql/describe.c
+++ b/src/bin/psql/describe.c
@@ -241,10 +241,15 @@ describeTablespaces(const char *pattern, bool verbose)
 		printACLColumn(&buf, "spcacl");
 		appendPQExpBuffer(&buf,
 						  ",\n  spcoptions AS \"%s\""
-						  ",\n  pg_catalog.pg_size_pretty(pg_catalog.pg_tablespace_size(oid)) AS \"%s\""
-						  ",\n  pg_catalog.shobj_description(oid, 'pg_tablespace') AS \"%s\"",
+						  ",\n  pg_catalog.pg_size_pretty(pg_catalog.pg_tablespace_size(oid)) AS \"%s\"",
 						  gettext_noop("Options"),
-						  gettext_noop("Size"),
+						  gettext_noop("Size"));
+		if (pset.sversion >= 180000)
+			appendPQExpBuffer(&buf,
+							  ",\n  pg_catalog.pg_size_pretty(pg_catalog.pg_tablespace_avail(oid)) AS \"%s\"",
+							  gettext_noop("Free"));
+		appendPQExpBuffer(&buf,
+						  ",\n  pg_catalog.shobj_description(oid, 'pg_tablespace') AS \"%s\"",
 						  gettext_noop("Description"));
 	}
 
diff --git a/src/include/catalog/pg_proc.dat b/src/include/catalog/pg_proc.dat
index 42e427f8fe8..9d64da6bfb8 100644
--- a/src/include/catalog/pg_proc.dat
+++ b/src/include/catalog/pg_proc.dat
@@ -7680,6 +7680,14 @@
   descr => 'total disk space usage for the specified tablespace',
   proname => 'pg_tablespace_size', provolatile => 'v', prorettype => 'int8',
   proargtypes => 'name', prosrc => 'pg_tablespace_size_name' },
+{ oid => '6015',
+  descr => 'disk stats for the specified tablespace',
+  proname => 'pg_tablespace_avail', provolatile => 'v', prorettype => 'int8',
+  proargtypes => 'oid', prosrc => 'pg_tablespace_avail_oid' },
+{ oid => '6016',
+  descr => 'disk stats for the specified tablespace',
+  proname => 'pg_tablespace_avail', provolatile => 'v', prorettype => 'int8',
+  proargtypes => 'name', prosrc => 'pg_tablespace_avail_name' },
 { oid => '2324', descr => 'total disk space usage for the specified database',
   proname => 'pg_database_size', provolatile => 'v', prorettype => 'int8',
   proargtypes => 'oid', prosrc => 'pg_database_size_oid' },
diff --git a/src/test/regress/expected/tablespace.out b/src/test/regress/expected/tablespace.out
index a90e39e5738..6709ed794df 100644
--- a/src/test/regress/expected/tablespace.out
+++ b/src/test/regress/expected/tablespace.out
@@ -20,6 +20,27 @@ SELECT spcoptions FROM pg_tablespace WHERE spcname = 'regress_tblspacewith';
  {random_page_cost=3.0}
 (1 row)
 
+-- check size functions
+SELECT pg_tablespace_size('pg_default') BETWEEN 1_000_000 and 10_000_000_000, -- rough sanity check
+       pg_tablespace_size('pg_global') BETWEEN 100_000 and 10_000_000,
+       pg_tablespace_size('regress_tblspacewith'); -- empty
+ ?column? | ?column? | pg_tablespace_size 
+----------+----------+--------------------
+ t        | t        |                  0
+(1 row)
+
+SELECT pg_tablespace_size('missing');
+ERROR:  tablespace "missing" does not exist
+SELECT pg_tablespace_avail('pg_default') > 1_000_000,
+       pg_tablespace_avail('pg_global') > 1_000_000,
+       pg_tablespace_avail('regress_tblspacewith') > 1_000_000;
+ ?column? | ?column? | ?column? 
+----------+----------+----------
+ t        | t        | t
+(1 row)
+
+SELECT pg_tablespace_avail('missing');
+ERROR:  tablespace "missing" does not exist
 -- drop the tablespace so we can re-use the location
 DROP TABLESPACE regress_tblspacewith;
 -- This returns a relative path as of an effect of allow_in_place_tablespaces,
diff --git a/src/test/regress/sql/tablespace.sql b/src/test/regress/sql/tablespace.sql
index dfe3db096e2..3fcd4bb00ff 100644
--- a/src/test/regress/sql/tablespace.sql
+++ b/src/test/regress/sql/tablespace.sql
@@ -17,6 +17,16 @@ CREATE TABLESPACE regress_tblspacewith LOCATION '' WITH (random_page_cost = 3.0)
 -- check to see the parameter was used
 SELECT spcoptions FROM pg_tablespace WHERE spcname = 'regress_tblspacewith';
 
+-- check size functions
+SELECT pg_tablespace_size('pg_default') BETWEEN 1_000_000 and 10_000_000_000, -- rough sanity check
+       pg_tablespace_size('pg_global') BETWEEN 100_000 and 10_000_000,
+       pg_tablespace_size('regress_tblspacewith'); -- empty
+SELECT pg_tablespace_size('missing');
+SELECT pg_tablespace_avail('pg_default') > 1_000_000,
+       pg_tablespace_avail('pg_global') > 1_000_000,
+       pg_tablespace_avail('regress_tblspacewith') > 1_000_000;
+SELECT pg_tablespace_avail('missing');
+
 -- drop the tablespace so we can re-use the location
 DROP TABLESPACE regress_tblspacewith;
 
-- 
2.47.2

Thomas Munro

thomas.munro@gmail.com

10 months ago

In reply to: Christoph Berg (#3)

Re: Available disk space per tablespace

On Sat, Mar 15, 2025 at 4:40 AM Christoph Berg <myon@debian.org> wrote:

I'm still unconvinced if we should use statfs() instead of statvfs()
on *BSD or if their manpage is just trolling us and statvfs is just
fine.

DESCRIPTION
The statvfs() and fstatvfs() functions fill the structure pointed to by
buf with garbage. This garbage will occasionally bear resemblance to
file system statistics, but portable applications must not depend on
this.

Hah, I see this in my local FreeBSD man page. I guess this might be a
reference to POSIX's 100% get-out clause "it is unspecified whether
all members of the statvfs structure have meaningful values on all
file systems". The statfs() man page doesn't say that (a nonstandard
syscall that originated in 4.4BSD, which POSIX decided to rename
because other systems sprouted incompatible statfs() interfaces?).
It's hard to imagine a system that doesn't track free space and report
it here, and if it doesn't, well so what, that's probably also a
system that can't report free space to the "df" command, so what are
we supposed to do? We could perhaps add a note to the documentation
that this field relies on the OS providing meaningful "avail" field in
statvfs(), but it's hard to imagine. Maybe just defer that until
someone shows up with a real report? So +1 from me, go for it, call
statvfs() and don't worry.

I tried your v3 patch on my FreeBSD 14.2 battle station:

That is the correct answer:

tmunro@build1:~/projects/postgresql/build $ df -h .
Filesystem Size Used Avail Capacity Mounted on
zroot/usr/home 331G 41G 290G 12% /usr/home

I also pushed your patch to CI and triggered the NetBSD and OpenBSD
tasks and they passed your sanity test, though that only checks that
the reported some number > 1MB.

I looked at the source, and on FreeBSD statvfs[1]https://github.com/freebsd/freebsd-src/blob/36782aaba4f1a7d054aa405357a8fa2bc0f94eb0/lib/libc/gen/statvfs.c#L70 is just a libc
function that calls statfs() (as does df). The statfs() man page has
no funny disclaimers. OpenBSD's[2]https://github.com/openbsd/src/blob/70ab9842eb8b368612eb098db19dcf94c19d673d/lib/libc/gen/statvfs.c#L59 too. NetBSD seems to have a real
statvfs (or statvfs1) syscall but its man page has no funny
disclaimers.

+#ifdef WIN32
+       if (GetDiskFreeSpaceEx(tblspcPath, &lpFreeBytesAvailable,
NULL, NULL) == false)
+               return -1;
+
+       return lpFreeBytesAvailable.QuadPart; /* ULONGLONG part of
ULARGE_INTEGER */
+#else
+       if (statvfs(tblspcPath, &fst) < 0)
+               return -1;
+
+       return fst.f_bavail * fst.f_frsize; /* available blocks times
fragment size */
+#endif

What's the rationale for not raising an error if the system call
fails? If someone complains that it's showing -1, doesn't that mean
we'll have to ask them to trace the system calls to figure out why, or
if it's Windows, likely abandon all hope of ever knowing why? Should
statvfs() retry on EINTR?

Style nit: maybe ! instead of == false?

Nice feature.

[1]: https://github.com/freebsd/freebsd-src/blob/36782aaba4f1a7d054aa405357a8fa2bc0f94eb0/lib/libc/gen/statvfs.c#L70
[2]: https://github.com/openbsd/src/blob/70ab9842eb8b368612eb098db19dcf94c19d673d/lib/libc/gen/statvfs.c#L59

Christoph Berg

myon@debian.org

10 months ago

In reply to: Thomas Munro (#4)

1 attachment(s)

Re: Available disk space per tablespace

Re: Thomas Munro

Hah, I see this in my local FreeBSD man page. I guess this might be a
reference to POSIX's 100% get-out clause "it is unspecified whether
all members of the statvfs structure have meaningful values on all
file systems".

Yeah I could hear someone being annoyed by POSIX echoed in that
paragraph.

system that can't report free space to the "df" command, so what are
we supposed to do? We could perhaps add a note to the documentation
that this field relies on the OS providing meaningful "avail" field in
statvfs(), but it's hard to imagine. Maybe just defer that until
someone shows up with a real report? So +1 from me, go for it, call
statvfs() and don't worry.

I was reading looking into gnulib's wrapper around this - it's also
basically calling statvfs() except on assorted older systems.

https://github.com/coreutils/gnulib/blob/master/lib/fsusage.c#L114

Do we care about any of these?

AIX
OSF/1
2.6 < glibc/Linux < 2.6.36
glibc/Linux < 2.6, 4.3BSD, SunOS 4, \
Mac OS X < 10.4, FreeBSD < 5.0, \
NetBSD < 3.0, OpenBSD < 4.4k
SunOS 4.1.2, 4.1.3, and 4.1.3_U1
4.4BSD and older NetBSD
SVR3, old Irix

If not, then statvfs seems safe.

I also pushed your patch to CI and triggered the NetBSD and OpenBSD
tasks and they passed your sanity test, though that only checks that
the reported some number > 1MB.

I thought about making that test "between 1MB and 10PB", but that
seemed silly - it's not testing much, and some day, someone will try
to run the test on a system where it will still fail.

What's the rationale for not raising an error if the system call
fails?

That's mirroring the behavior of calculate_tablespace_size() in the
same file. I thought that's to allow \db+ to succeed even if some of
the tablespaces are botched/missing/whatever. But now on closer
inspection, I see that db_dir_size() is erroring out on problems, it
just ignores the top-level directory missing. Fixed in the attached
patch.

\db+
FEHLER: XX000: could not statvfs directory "pg_tblspc/16384/PG_18_202503111": Zu viele Ebenen aus symbolischen Links
LOCATION: calculate_tablespace_avail, dbsize.c:373

But this is actually something I wanted to address in a follow-up
patch: Currently, non-superusers cannot run \db+ because they lack
CREATE on pg_global (but `\db+ pg_default` works). Should we rather
make pg_database_size and pg_database_avail return NULL for
insufficient permissions instead of throwing an error?

If someone complains that it's showing -1, doesn't that mean

(-1 is translated to NULL for the SQL level.)

we'll have to ask them to trace the system calls to figure out why, or
if it's Windows, likely abandon all hope of ever knowing why? Should
statvfs() retry on EINTR?

Hmm. Is looping on EINTR worth the trouble?

Style nit: maybe ! instead of == false?

Changed.

Nice feature.

Thanks!

Christoph

Attachments:

v4-0001-Add-pg_tablespace_avail-functions.patchtext/x-diff; charset=us-asciiDownload

From db42fdcc5ee3097b3364ec51602d6d58994b2060 Mon Sep 17 00:00:00 2001
From: Christoph Berg <myon@debian.org>
Date: Fri, 14 Mar 2025 16:29:19 +0100
Subject: [PATCH v4] Add pg_tablespace_avail() functions

This exposes the f_avail value from statvfs() on tablespace directories
on the SQL level, allowing monitoring of free disk space from within the
server. On windows, GetDiskFreeSpaceEx() is used.

Permissions required match those from pg_tablespace_size().

In psql, include a new "Free" column in \db+ output.

Add test coverage for pg_tablespace_avail() and the previously not
covered pg_tablespace_size() function.
---
 doc/src/sgml/func.sgml                   |  21 +++++
 doc/src/sgml/ref/psql-ref.sgml           |   2 +-
 src/backend/utils/adt/dbsize.c           | 102 +++++++++++++++++++++++
 src/bin/psql/describe.c                  |  11 ++-
 src/include/catalog/pg_proc.dat          |   8 ++
 src/test/regress/expected/tablespace.out |  21 +++++
 src/test/regress/sql/tablespace.sql      |  10 +++
 7 files changed, 171 insertions(+), 4 deletions(-)

diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml
index 51dd8ad6571..0b4456ad958 100644
--- a/doc/src/sgml/func.sgml
+++ b/doc/src/sgml/func.sgml
@@ -30093,6 +30093,27 @@ postgres=# SELECT '0/0'::pg_lsn + pd.segment_number * ps.setting::int + :offset
        </para></entry>
       </row>
 
+      <row>
+       <entry role="func_table_entry"><para role="func_signature">
+        <indexterm>
+         <primary>pg_tablespace_avail</primary>
+        </indexterm>
+        <function>pg_tablespace_avail</function> ( <type>name</type> )
+        <returnvalue>bigint</returnvalue>
+       </para>
+       <para role="func_signature">
+        <function>pg_tablespace_avail</function> ( <type>oid</type> )
+        <returnvalue>bigint</returnvalue>
+       </para>
+       <para>
+        Returns the available disk space in the tablespace with the
+        specified name or OID. To use this function, you must
+        have <literal>CREATE</literal> privilege on the specified tablespace
+        or have privileges of the <literal>pg_read_all_stats</literal> role,
+        unless it is the default tablespace for the current database.
+       </para></entry>
+      </row>
+
       <row>
        <entry role="func_table_entry"><para role="func_signature">
         <indexterm>
diff --git a/doc/src/sgml/ref/psql-ref.sgml b/doc/src/sgml/ref/psql-ref.sgml
index cedccc14129..9e1bec0b422 100644
--- a/doc/src/sgml/ref/psql-ref.sgml
+++ b/doc/src/sgml/ref/psql-ref.sgml
@@ -1492,7 +1492,7 @@ SELECT $1 \parse stmt1
         If <literal>x</literal> is appended to the command name, the results
         are displayed in expanded mode.
         If <literal>+</literal> is appended to the command name, each tablespace
-        is listed with its associated options, on-disk size, permissions and
+        is listed with its associated options, on-disk size and free disk space, permissions and
         description.
         </para>
         </listitem>
diff --git a/src/backend/utils/adt/dbsize.c b/src/backend/utils/adt/dbsize.c
index 25865b660ef..9bd8667c2d9 100644
--- a/src/backend/utils/adt/dbsize.c
+++ b/src/backend/utils/adt/dbsize.c
@@ -12,6 +12,12 @@
 #include "postgres.h"
 
 #include <sys/stat.h>
+#ifdef WIN32
+#include <fileapi.h>
+#include <errhandlingapi.h>
+#else
+#include <sys/statvfs.h>
+#endif
 
 #include "access/htup_details.h"
 #include "access/relation.h"
@@ -316,6 +322,102 @@ pg_tablespace_size_name(PG_FUNCTION_ARGS)
 }
 
 
+/*
+ * Return available disk space of tablespace. Returns -1 if the tablespace
+ * directory cannot be found.
+ */
+static int64
+calculate_tablespace_avail(Oid tblspcOid)
+{
+	char		tblspcPath[MAXPGPATH];
+	AclResult	aclresult;
+#ifdef WIN32
+	ULARGE_INTEGER lpFreeBytesAvailable;
+#else
+	struct statvfs fst;
+#endif
+
+	/*
+	 * User must have privileges of pg_read_all_stats or have CREATE privilege
+	 * for target tablespace, either explicitly granted or implicitly because
+	 * it is default for current database.
+	 */
+	if (tblspcOid != MyDatabaseTableSpace &&
+		!has_privs_of_role(GetUserId(), ROLE_PG_READ_ALL_STATS))
+	{
+		aclresult = object_aclcheck(TableSpaceRelationId, tblspcOid, GetUserId(), ACL_CREATE);
+		if (aclresult != ACLCHECK_OK)
+			aclcheck_error(aclresult, OBJECT_TABLESPACE,
+						   get_tablespace_name(tblspcOid));
+	}
+
+	if (tblspcOid == DEFAULTTABLESPACE_OID)
+		snprintf(tblspcPath, MAXPGPATH, "base");
+	else if (tblspcOid == GLOBALTABLESPACE_OID)
+		snprintf(tblspcPath, MAXPGPATH, "global");
+	else
+		snprintf(tblspcPath, MAXPGPATH, "%s/%u/%s", PG_TBLSPC_DIR, tblspcOid,
+				 TABLESPACE_VERSION_DIRECTORY);
+
+#ifdef WIN32
+	if (! GetDiskFreeSpaceEx(tblspcPath, &lpFreeBytesAvailable, NULL, NULL))
+		elog(ERROR, "GetDiskFreeSpaceEx failed: error code %lu", GetLastError());
+
+	return lpFreeBytesAvailable.QuadPart; /* ULONGLONG part of ULARGE_INTEGER */
+#else
+	if (statvfs(tblspcPath, &fst) < 0)
+	{
+		if (errno == ENOENT)
+			return -1;
+		else
+			ereport(ERROR,
+					(errcode_for_file_access(),
+					 errmsg("could not statvfs directory \"%s\": %m", tblspcPath)));
+	}
+
+	return fst.f_bavail * fst.f_frsize; /* available blocks times fragment size */
+#endif
+}
+
+Datum
+pg_tablespace_avail_oid(PG_FUNCTION_ARGS)
+{
+	Oid			tblspcOid = PG_GETARG_OID(0);
+	int64		avail;
+
+	/*
+	 * Not needed for correctness, but avoid non-user-facing error message
+	 * later if the tablespace doesn't exist.
+	 */
+	if (!SearchSysCacheExists1(TABLESPACEOID, ObjectIdGetDatum(tblspcOid)))
+		ereport(ERROR,
+				errcode(ERRCODE_UNDEFINED_OBJECT),
+				errmsg("tablespace with OID %u does not exist", tblspcOid));
+
+	avail = calculate_tablespace_avail(tblspcOid);
+
+	if (avail < 0)
+		PG_RETURN_NULL();
+
+	PG_RETURN_INT64(avail);
+}
+
+Datum
+pg_tablespace_avail_name(PG_FUNCTION_ARGS)
+{
+	Name		tblspcName = PG_GETARG_NAME(0);
+	Oid			tblspcOid = get_tablespace_oid(NameStr(*tblspcName), false);
+	int64		avail;
+
+	avail = calculate_tablespace_avail(tblspcOid);
+
+	if (avail < 0)
+		PG_RETURN_NULL();
+
+	PG_RETURN_INT64(avail);
+}
+
+
 /*
  * calculate size of (one fork of) a relation
  *
diff --git a/src/bin/psql/describe.c b/src/bin/psql/describe.c
index e6cf468ac9e..8c52a126ac1 100644
--- a/src/bin/psql/describe.c
+++ b/src/bin/psql/describe.c
@@ -241,10 +241,15 @@ describeTablespaces(const char *pattern, bool verbose)
 		printACLColumn(&buf, "spcacl");
 		appendPQExpBuffer(&buf,
 						  ",\n  spcoptions AS \"%s\""
-						  ",\n  pg_catalog.pg_size_pretty(pg_catalog.pg_tablespace_size(oid)) AS \"%s\""
-						  ",\n  pg_catalog.shobj_description(oid, 'pg_tablespace') AS \"%s\"",
+						  ",\n  pg_catalog.pg_size_pretty(pg_catalog.pg_tablespace_size(oid)) AS \"%s\"",
 						  gettext_noop("Options"),
-						  gettext_noop("Size"),
+						  gettext_noop("Size"));
+		if (pset.sversion >= 180000)
+			appendPQExpBuffer(&buf,
+							  ",\n  pg_catalog.pg_size_pretty(pg_catalog.pg_tablespace_avail(oid)) AS \"%s\"",
+							  gettext_noop("Free"));
+		appendPQExpBuffer(&buf,
+						  ",\n  pg_catalog.shobj_description(oid, 'pg_tablespace') AS \"%s\"",
 						  gettext_noop("Description"));
 	}
 
diff --git a/src/include/catalog/pg_proc.dat b/src/include/catalog/pg_proc.dat
index 42e427f8fe8..9d64da6bfb8 100644
--- a/src/include/catalog/pg_proc.dat
+++ b/src/include/catalog/pg_proc.dat
@@ -7680,6 +7680,14 @@
   descr => 'total disk space usage for the specified tablespace',
   proname => 'pg_tablespace_size', provolatile => 'v', prorettype => 'int8',
   proargtypes => 'name', prosrc => 'pg_tablespace_size_name' },
+{ oid => '6015',
+  descr => 'disk stats for the specified tablespace',
+  proname => 'pg_tablespace_avail', provolatile => 'v', prorettype => 'int8',
+  proargtypes => 'oid', prosrc => 'pg_tablespace_avail_oid' },
+{ oid => '6016',
+  descr => 'disk stats for the specified tablespace',
+  proname => 'pg_tablespace_avail', provolatile => 'v', prorettype => 'int8',
+  proargtypes => 'name', prosrc => 'pg_tablespace_avail_name' },
 { oid => '2324', descr => 'total disk space usage for the specified database',
   proname => 'pg_database_size', provolatile => 'v', prorettype => 'int8',
   proargtypes => 'oid', prosrc => 'pg_database_size_oid' },
diff --git a/src/test/regress/expected/tablespace.out b/src/test/regress/expected/tablespace.out
index a90e39e5738..6709ed794df 100644
--- a/src/test/regress/expected/tablespace.out
+++ b/src/test/regress/expected/tablespace.out
@@ -20,6 +20,27 @@ SELECT spcoptions FROM pg_tablespace WHERE spcname = 'regress_tblspacewith';
  {random_page_cost=3.0}
 (1 row)
 
+-- check size functions
+SELECT pg_tablespace_size('pg_default') BETWEEN 1_000_000 and 10_000_000_000, -- rough sanity check
+       pg_tablespace_size('pg_global') BETWEEN 100_000 and 10_000_000,
+       pg_tablespace_size('regress_tblspacewith'); -- empty
+ ?column? | ?column? | pg_tablespace_size 
+----------+----------+--------------------
+ t        | t        |                  0
+(1 row)
+
+SELECT pg_tablespace_size('missing');
+ERROR:  tablespace "missing" does not exist
+SELECT pg_tablespace_avail('pg_default') > 1_000_000,
+       pg_tablespace_avail('pg_global') > 1_000_000,
+       pg_tablespace_avail('regress_tblspacewith') > 1_000_000;
+ ?column? | ?column? | ?column? 
+----------+----------+----------
+ t        | t        | t
+(1 row)
+
+SELECT pg_tablespace_avail('missing');
+ERROR:  tablespace "missing" does not exist
 -- drop the tablespace so we can re-use the location
 DROP TABLESPACE regress_tblspacewith;
 -- This returns a relative path as of an effect of allow_in_place_tablespaces,
diff --git a/src/test/regress/sql/tablespace.sql b/src/test/regress/sql/tablespace.sql
index dfe3db096e2..3fcd4bb00ff 100644
--- a/src/test/regress/sql/tablespace.sql
+++ b/src/test/regress/sql/tablespace.sql
@@ -17,6 +17,16 @@ CREATE TABLESPACE regress_tblspacewith LOCATION '' WITH (random_page_cost = 3.0)
 -- check to see the parameter was used
 SELECT spcoptions FROM pg_tablespace WHERE spcname = 'regress_tblspacewith';
 
+-- check size functions
+SELECT pg_tablespace_size('pg_default') BETWEEN 1_000_000 and 10_000_000_000, -- rough sanity check
+       pg_tablespace_size('pg_global') BETWEEN 100_000 and 10_000_000,
+       pg_tablespace_size('regress_tblspacewith'); -- empty
+SELECT pg_tablespace_size('missing');
+SELECT pg_tablespace_avail('pg_default') > 1_000_000,
+       pg_tablespace_avail('pg_global') > 1_000_000,
+       pg_tablespace_avail('regress_tblspacewith') > 1_000_000;
+SELECT pg_tablespace_avail('missing');
+
 -- drop the tablespace so we can re-use the location
 DROP TABLESPACE regress_tblspacewith;
 
-- 
2.47.2

Laurenz Albe

laurenz.albe@cybertec.at

10 months ago

In reply to: Christoph Berg (#5)

Re: Available disk space per tablespace

On Sat, 2025-03-15 at 13:09 +0100, Christoph Berg wrote:

Do we care about any of these?

AIX

We dropped support for it, but there are efforts to change that.

Yours,
Laurenz Albe

Thomas Munro

thomas.munro@gmail.com

10 months ago

In reply to: Laurenz Albe (#6)

Re: Available disk space per tablespace

On Sun, Mar 16, 2025 at 1:17 AM Laurenz Albe <laurenz.albe@cybertec.at> wrote:

On Sat, 2025-03-15 at 13:09 +0100, Christoph Berg wrote:

Do we care about any of these?

AIX

We dropped support for it, but there are efforts to change that.

FWIW AIX does have it, according to its manual, in case it comes back.
The others in the list are defunct or obsolete versions.

Thomas Munro

thomas.munro@gmail.com

10 months ago

In reply to: Christoph Berg (#5)

Re: Available disk space per tablespace

On Sun, Mar 16, 2025 at 1:09 AM Christoph Berg <myon@debian.org> wrote:

Hmm. Is looping on EINTR worth the trouble?

I was just wondering if it might be one of those oddballs that ignores
SA_RESTART, but I guess that doesn't seem too likely (I mean, first
you'd probably have to have a reason to sleep or some other special
reason, and who knows what some unusual file systems might do). It
certainly doesn't on the systems I tried. So I guess not until we
have other evidence.

Christoph Berg

myon@debian.org

10 months ago

In reply to: Thomas Munro (#8)

Re: Available disk space per tablespace

Re: Thomas Munro

Hmm. Is looping on EINTR worth the trouble?

I was just wondering if it might be one of those oddballs that ignores
SA_RESTART, but I guess that doesn't seem too likely (I mean, first
you'd probably have to have a reason to sleep or some other special
reason, and who knows what some unusual file systems might do). It
certainly doesn't on the systems I tried. So I guess not until we
have other evidence.

Gnulib's get_fs_usage() (which is what GNU coreutil's df uses)
does not handle EINTR either.

There is some code that does int width expansion, but I believe we
don't need that since the `fst.f_bavail * fst.f_frsize` multiplication
takes care of converting that to int64 (if it wasn't already 64bits
before).

Christoph

#10

said assemlal

oyoun@gmx.com

9 months ago

In reply to: Christoph Berg (#1)

Re: Available disk space per tablespace

Hi,

I also tested the patch on Linux mint 22.1 with the btrfs and ext4
partitions. I generated some data and the outcome looks good:

Numbers are the same as if I were executing the command: df -h

tablespace_test2 was the ext4 partition on usb stick.

Numbers are correct.

Said

Show quoted text

On 2025-03-13 14 h 10, Christoph Berg wrote:

Hi,

I'm picking up a 5 year old patch again:
/messages/by-id/20191108132419.GG8017@msg.df7cb.de

Users will be interested in knowing how much extra data they can load
into a database, but PG currently does not expose that number. This
patch introduces a new function pg_tablespace_avail() that takes a
tablespace name or oid, and returns the number of bytes "available"
there. This is the number without any reserved blocks (Unix, f_avail)
or available to the current user (Windows).

(This is not meant to replace a full-fledged OS monitoring system that
has much more numbers about disks and everything, it is filling a UX
gap.)

Compared to the last patch, this just returns a single number so it's
easier to use - total space isn't all that interesting, we just return
the number the user wants.

The free space is included in \db+ output:

postgres =# \db+
List of tablespaces
Name │ Owner │ Location │ Access privileges │ Options │ Size │ Free │ Description
────────────┼───────┼──────────┼───────────────────┼─────────┼─────────┼────────┼─────────────
pg_default │ myon │ │ ∅ │ ∅ │ 23 MB │ 538 GB │ ∅
pg_global │ myon │ │ ∅ │ ∅ │ 556 kB │ 538 GB │ ∅
spc │ myon │ /tmp/spc │ ∅ │ ∅ │ 0 bytes │ 31 GB │ ∅
(3 rows)

The patch has also been tested on Windows.

TODO: Figure out which systems need statfs() vs statvfs()

Christoph