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
>From db42fdcc5ee3097b3364ec51602d6d58994b2060 Mon Sep 17 00:00:00 2001
From: Christoph Berg <m...@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
