Hello Solai,
On Mon, Aug 24, 2026 at 8:31 AM solai v <[email protected]> wrote:
>
> Thank you for the updated patches. I have completed the review and
> testing of the v5 patch series for introducing the pg_stat_vfdcache
> view and VFD cache footprint metrics. I tested the patch on PostgreSQL
> 20devel with the debug and assertion-enabled build and verified the
> following:
>
> 1. Successfully built and ran the patched PostgreSQL tree.
> 2. Verified the newly introduced pg_stat_vfdcache view and its
> reported statistics.
> 3. Tested VFD hit/miss accounting through repeated table accesses.
> 4. Tested VFD cache behavior using a partitioned table with 1500
> partitions and 1.5 million rows.
> 5. Tested VFD pressure with a reduced max_files_per_process setting.
> 6. Verified the behavior of: hits, misses, open_entries,
> allocated_entries, cache_bytes, max_open_fds, and hit_ratio.
> 7. Tested repeated scans and observed the corresponding changes in VFD
> cache statistics.
> 8. Tested statistics reset using pg_stat_reset_shared('vfdcache').
> 9. Verified the behavior across multiple backend sessions.
> 10. Tested the statistics behavior across server restart.
> 11. Inspected the implementation of VFD cache footprint accounting in
> fd.c, including VFD allocation, reuse, filename allocation/freeing,
> and error handling.
>
Thanks for the thorough review.
>
> And also reviewed the statistics flush mechanism and confirmed that
> VFD hit/miss counters are maintained locally and flushed through the
> existing fixed-statistics infrastructure rather than taking a
> shared-memory lock on every VFD access.
> The main point I noticed is related to regression test coverage. The
> current regression test verifies that pg_stat_reset_shared('vfdcache')
> updates the stats_reset timestamp, but it does not directly exercise
> and verify the newly introduced VFD statistics such as hits, misses,
> open_entries, allocated_entries, and cache_bytes. I suggest adding a
> focused regression test covering the actual VFD activity and the newly
> exposed statistics, while avoiding assertions on fragile exact counter
> values where appropriate.
> Apart from these, I did not observe any functional issues during my
> testing and the patch looks good to me.
I rebased the patch (attached).
I agree that the patch needs some activity tests.
For hits & missed, i find a before/after test following the `pg_stat_wal`
pattern is good:
SELECT hits + misses AS vfd_accesses_before FROM pg_stat_vfdcache \gset
CREATE TEMP TABLE vfd_activity_test (i int);
INSERT INTO vfd_activity_test SELECT generate_series(1, 100);
SELECT count(*) FROM vfd_activity_test;
SELECT pg_stat_force_next_flush();
SELECT hits + misses > :vfd_accesses_before FROM pg_stat_vfdcache;
DROP TABLE vfd_activity_test;
For open_entries, allocated_entries, cache_bytes delta tests are not
reliable, open_entries can decrease between activity and measurement as
files are closed. `allocated_entries` is non-decreasing within a single
backend's lifetime, but the view sums across all backends ; any other
activity's effects (like vacuum) might mislead the test a bit.
For the latter counters, we can do some asserts like:
SELECT open_entries <= allocated_entries AS footprint_invariant
FROM pg_stat_vfdcache;
This for example means we never report more open FDs than allocated slots,
which should always be true (and perhaps other tests similar to this).
Do you agree with this, or do you have other recommendations? I will
proceed with v6 once we have alignment on this.
Regards,
Ayoub
From 6176556358eb96e07b95f0c9402949018f078659 Mon Sep 17 00:00:00 2001
From: AyoubKAZ <[email protected]>
Date: Tue, 25 Aug 2026 00:46:15 +0200
Subject: [PATCH v5 1/2] Add pg_stat_vfdcache view for VFD cache statistics
PostgreSQL's virtual file descriptor (VFD) layer maintains a
per-backend cache of open file descriptors bounded by
max_files_per_process (default 1000). When the cache is full, the
least-recently-used entry is evicted (its OS fd closed) so a new file
can be opened. A subsequent access to an evicted file must call
open() again.
A trivial example is with partitioned tables: a table with 1500
partitions requires up to many file descriptors per full scan (main
fork, vm ...), which is more than the default limit, causing
potential evictions and reopens.
This commit adds:
pg_stat_vfdcache -- a single-row view exposing cluster-wide VFD cache
statistics:
hits number of VFD cache hits
misses number of VFD cache misses
max_open_fds maximum number of file descriptors available to each backend process
hit_ratio hits / (hits + misses)
stats_reset timestamp of last counter reset
pg_stat_reset_vfdcache() -- resets shared VFD counters
The implementation follows the same cumulative shared statistics
infrastructure like pgstat_bgwriter and others do.
Event counting remains cheap in backend-local pending storage and is
flushed into shared fixed stats which requires locking.
Hit and miss counters are placed in FileAccess(), which is the
single gate through which all VFD-mediated file reads, writes,
truncations, and size checks pass.
---
doc/src/sgml/monitoring.sgml | 107 ++++++++++++++++++
src/backend/catalog/system_views.sql | 16 +++
src/backend/storage/file/fd.c | 5 +-
src/backend/utils/activity/Makefile | 1 +
src/backend/utils/activity/meson.build | 1 +
src/backend/utils/activity/pgstat.c | 17 +++
src/backend/utils/activity/pgstat_vfdcache.c | 113 +++++++++++++++++++
src/backend/utils/adt/pgstatfuncs.c | 47 +++++++-
src/include/catalog/pg_proc.dat | 30 +++++
src/include/pgstat.h | 26 +++++
src/include/utils/pgstat_internal.h | 22 +++-
src/include/utils/pgstat_kind.h | 3 +-
src/test/regress/expected/rules.out | 8 ++
src/test/regress/expected/stats.out | 19 +++-
src/test/regress/sql/stats.sql | 5 +
15 files changed, 414 insertions(+), 6 deletions(-)
create mode 100644 src/backend/utils/activity/pgstat_vfdcache.c
diff --git a/doc/src/sgml/monitoring.sgml b/doc/src/sgml/monitoring.sgml
index 32cb6fdbd76..d2997c4d090 100644
--- a/doc/src/sgml/monitoring.sgml
+++ b/doc/src/sgml/monitoring.sgml
@@ -563,6 +563,15 @@ postgres 27093 0.0 0.0 30096 2752 ? Ss 11:34 0:00 postgres: ser
</entry>
</row>
+ <row>
+ <entry><structname>pg_stat_vfdcache</structname><indexterm><primary>pg_stat_vfdcache</primary></indexterm></entry>
+ <entry>One row only, showing cluster-wide statistics about virtual file
+ descriptor (VFD) cache activity. See
+ <link linkend="monitoring-pg-stat-vfdcache-view">
+ <structname>pg_stat_vfdcache</structname></link> for details.
+ </entry>
+ </row>
+
<row>
<entry><structname>pg_stat_wal</structname><indexterm><primary>pg_stat_wal</primary></indexterm></entry>
<entry>One row only, showing statistics about WAL activity. See
@@ -3909,6 +3918,89 @@ description | Waiting for a newly initialized WAL file to reach durable storage
</para>
</sect2>
+ <sect2 id="monitoring-pg-stat-vfdcache-view">
+ <title><structname>pg_stat_vfdcache</structname></title>
+
+ <indexterm zone="monitoring-pg-stat-vfdcache-view">
+ <primary>pg_stat_vfdcache</primary>
+ </indexterm>
+
+ <para>
+ The <structname>pg_stat_vfdcache</structname> view will always have a
+ single row, containing data about cluster-wide VFD (Virtual File
+ Descriptor) cache activity.
+ </para>
+
+ <table id="pg-stat-vfdcache-view" xreflabel="pg_stat_vfdcache">
+ <title><structname>pg_stat_vfdcache</structname> View</title>
+ <tgroup cols="1">
+ <thead>
+ <row>
+ <entry role="catalog_table_entry"><para role="column_definition">
+ Column Type
+ </para>
+ <para>
+ Description
+ </para></entry>
+ </row>
+ </thead>
+
+ <tbody>
+ <row>
+ <entry role="catalog_table_entry"><para role="column_definition">
+ <structfield>hits</structfield> <type>bigint</type>
+ </para>
+ <para>
+ Number of file accesses where the physical file descriptor was
+ already open in the cache, requiring no system call
+ </para></entry>
+ </row>
+
+ <row>
+ <entry role="catalog_table_entry"><para role="column_definition">
+ <structfield>misses</structfield> <type>bigint</type>
+ </para>
+ <para>
+ Number of file accesses where the physical file descriptor had
+ been evicted from the cache, requiring <function>open()</function>
+ to be called again before the access could proceed
+ </para></entry>
+ </row>
+
+ <row>
+ <entry role="catalog_table_entry"><para role="column_definition">
+ <structfield>max_open_fds</structfield> <type>integer</type>
+ </para>
+ <para>
+ Maximum number of file descriptors available to each backend process
+ </para></entry>
+ </row>
+
+ <row>
+ <entry role="catalog_table_entry"><para role="column_definition">
+ <structfield>hit_ratio</structfield> <type>float8</type>
+ </para>
+ <para>
+ Fraction of file accesses that were cache hits:
+ <literal>hits / (hits + misses)</literal>
+ </para></entry>
+ </row>
+
+ <row>
+ <entry role="catalog_table_entry"><para role="column_definition">
+ <structfield>stats_reset</structfield> <type>timestamp with time zone</type>
+ </para>
+ <para>
+ Time at which the counters were last reset by
+ <function>pg_stat_reset_vfdcache()</function>
+ </para></entry>
+ </row>
+ </tbody>
+ </tgroup>
+ </table>
+
+ </sect2>
+
<sect2 id="monitoring-pg-stat-wal-view">
<title><structname>pg_stat_wal</structname></title>
@@ -6157,6 +6249,21 @@ description | Waiting for a newly initialized WAL file to reach durable storage
can be granted EXECUTE to run the function.
</para></entry>
</row>
+
+ <row>
+ <entry role="func_table_entry"><para role="func_signature">
+ <indexterm>
+ <primary>pg_stat_reset_vfdcache</primary>
+ </indexterm>
+ <function>pg_stat_reset_vfdcache</function> ()
+ <returnvalue>void</returnvalue>
+ </para>
+ <para>
+ Reset shared VFD cache statistics counters to zero. The reset
+ timestamp is recorded in
+ <structname>pg_stat_vfdcache</structname>.<structfield>stats_reset</structfield>.
+ </para></entry>
+ </row>
</tbody>
</tgroup>
</table>
diff --git a/src/backend/catalog/system_views.sql b/src/backend/catalog/system_views.sql
index 8612d99a890..844fea1391f 100644
--- a/src/backend/catalog/system_views.sql
+++ b/src/backend/catalog/system_views.sql
@@ -1568,3 +1568,19 @@ CREATE VIEW pg_aios AS
SELECT * FROM pg_get_aios();
REVOKE ALL ON pg_aios FROM PUBLIC;
GRANT SELECT ON pg_aios TO pg_read_all_stats;
+
+CREATE VIEW pg_stat_vfdcache AS
+ SELECT
+ pg_stat_get_vfd_hits() AS hits,
+ pg_stat_get_vfd_misses() AS misses,
+ pg_stat_get_vfd_max_open_fds() AS max_open_fds,
+ CASE
+ WHEN pg_stat_get_vfd_hits() + pg_stat_get_vfd_misses() = 0
+ THEN NULL::float8
+ ELSE pg_stat_get_vfd_hits()::float8
+ / (pg_stat_get_vfd_hits() + pg_stat_get_vfd_misses())
+ END AS hit_ratio,
+ pg_stat_get_vfd_stat_reset_time() AS stats_reset;
+
+REVOKE ALL ON pg_stat_vfdcache FROM PUBLIC;
+GRANT SELECT ON pg_stat_vfdcache TO PUBLIC;
diff --git a/src/backend/storage/file/fd.c b/src/backend/storage/file/fd.c
index 190c9974494..d2436ed953e 100644
--- a/src/backend/storage/file/fd.c
+++ b/src/backend/storage/file/fd.c
@@ -1480,6 +1480,7 @@ static int
FileAccess(File file)
{
int returnValue;
+ bool is_open;
DO_DB(elog(LOG, "FileAccess %d (%s)",
file, VfdCache[file].fileName));
@@ -1488,8 +1489,10 @@ FileAccess(File file)
* Is the file open? If not, open it and put it at the head of the LRU
* ring (possibly closing the least recently used file to get an FD).
*/
+ is_open = !FileIsNotOpen(file);
+ pgstat_count_vfd_access(is_open);
- if (FileIsNotOpen(file))
+ if (!is_open)
{
returnValue = LruInsert(file);
if (returnValue != 0)
diff --git a/src/backend/utils/activity/Makefile b/src/backend/utils/activity/Makefile
index 2e32d1485d6..264e170bb95 100644
--- a/src/backend/utils/activity/Makefile
+++ b/src/backend/utils/activity/Makefile
@@ -34,6 +34,7 @@ OBJS = \
pgstat_shmem.o \
pgstat_slru.o \
pgstat_subscription.o \
+ pgstat_vfdcache.o \
pgstat_wal.o \
pgstat_xact.o \
wait_event.o \
diff --git a/src/backend/utils/activity/meson.build b/src/backend/utils/activity/meson.build
index e6dcb2e26fc..4ac9c5e93e1 100644
--- a/src/backend/utils/activity/meson.build
+++ b/src/backend/utils/activity/meson.build
@@ -19,6 +19,7 @@ backend_sources += files(
'pgstat_shmem.c',
'pgstat_slru.c',
'pgstat_subscription.c',
+ 'pgstat_vfdcache.c',
'pgstat_wal.c',
'pgstat_xact.c',
)
diff --git a/src/backend/utils/activity/pgstat.c b/src/backend/utils/activity/pgstat.c
index 4615f610106..e82ad3918fe 100644
--- a/src/backend/utils/activity/pgstat.c
+++ b/src/backend/utils/activity/pgstat.c
@@ -516,6 +516,23 @@ static const PgStat_KindInfo pgstat_kind_builtin_infos[PGSTAT_KIND_BUILTIN_SIZE]
.reset_all_cb = pgstat_wal_reset_all_cb,
.snapshot_cb = pgstat_wal_snapshot_cb,
},
+
+ [PGSTAT_KIND_VFDCACHE] = {
+ .name = "vfdcache",
+
+ .fixed_amount = true,
+ .write_to_file = true,
+
+ .snapshot_ctl_off = offsetof(PgStat_Snapshot, vfdcache),
+ .shared_ctl_off = offsetof(PgStat_ShmemControl, vfdcache),
+ .shared_data_off = offsetof(PgStatShared_VfdCache, stats),
+ .shared_data_len = sizeof(((PgStatShared_VfdCache *) 0)->stats),
+
+ .flush_static_cb = pgstat_vfdcache_flush_cb,
+ .init_shmem_cb = pgstat_vfdcache_init_shmem_cb,
+ .reset_all_cb = pgstat_vfdcache_reset_all_cb,
+ .snapshot_cb = pgstat_vfdcache_snapshot_cb,
+ },
};
/*
diff --git a/src/backend/utils/activity/pgstat_vfdcache.c b/src/backend/utils/activity/pgstat_vfdcache.c
new file mode 100644
index 00000000000..b036759031c
--- /dev/null
+++ b/src/backend/utils/activity/pgstat_vfdcache.c
@@ -0,0 +1,113 @@
+/* -------------------------------------------------------------------------
+ *
+ * pgstat_vfdcache.c
+ * Implementation of VFD cache statistics.
+ *
+ * VFD events are first counted in backend-local pending storage and then
+ * flushed into shared-memory cumulative stats, following the same model as
+ * other fixed stats kinds.
+ *
+ * Portions Copyright (c) 1996-2026, PostgreSQL Global Development Group
+ *
+ * IDENTIFICATION
+ * src/backend/utils/activity/pgstat_vfdcache.c
+ * -------------------------------------------------------------------------
+ */
+
+#include "postgres.h"
+
+#include "pgstat.h"
+#include "utils/memutils.h"
+#include "utils/pgstat_internal.h"
+
+/*
+ * Backend-local VFD counters waiting to be flushed.
+ */
+PgStat_VfdCacheStats PendingVfdCacheStats = {0};
+
+/*
+ * Count a VFD cache access as either a hit or miss.
+ */
+void
+pgstat_count_vfd_access(bool hit)
+{
+ if (hit)
+ PendingVfdCacheStats.vfd_hits++;
+ else
+ PendingVfdCacheStats.vfd_misses++;
+ pgstat_report_fixed = true;
+}
+
+/*
+ * Flush out backend-local pending VFD cache stats.
+ */
+bool
+pgstat_vfdcache_flush_cb(bool nowait)
+{
+ PgStatShared_VfdCache *stats_shmem = &pgStatLocal.shmem->vfdcache;
+
+ if (pg_memory_is_all_zeros(&PendingVfdCacheStats,
+ sizeof(struct PgStat_VfdCacheStats)))
+ return false;
+
+ if (!nowait)
+ LWLockAcquire(&stats_shmem->lock, LW_EXCLUSIVE);
+ else if (!LWLockConditionalAcquire(&stats_shmem->lock, LW_EXCLUSIVE))
+ return true;
+
+ stats_shmem->stats.vfd_hits += PendingVfdCacheStats.vfd_hits;
+ stats_shmem->stats.vfd_misses += PendingVfdCacheStats.vfd_misses;
+
+ LWLockRelease(&stats_shmem->lock);
+
+ MemSet(&PendingVfdCacheStats, 0, sizeof(PendingVfdCacheStats));
+
+ return false;
+}
+
+/*
+ * Support function for SQL-callable pg_stat_get_vfd_* functions.
+ */
+PgStat_VfdCacheStats *
+pgstat_fetch_stat_vfdcache(void)
+{
+ pgstat_snapshot_fixed(PGSTAT_KIND_VFDCACHE);
+
+ return &pgStatLocal.snapshot.vfdcache;
+}
+
+void
+pgstat_vfdcache_init_shmem_cb(void *stats)
+{
+ PgStatShared_VfdCache *stats_shmem = (PgStatShared_VfdCache *) stats;
+
+ LWLockInitialize(&stats_shmem->lock, LWTRANCHE_PGSTATS_DATA);
+}
+
+void
+pgstat_vfdcache_reset_all_cb(TimestampTz ts)
+{
+ PgStatShared_VfdCache *stats_shmem = &pgStatLocal.shmem->vfdcache;
+
+ LWLockAcquire(&stats_shmem->lock, LW_EXCLUSIVE);
+ MemSet(&stats_shmem->stats, 0, sizeof(stats_shmem->stats));
+ stats_shmem->stats.stat_reset_timestamp = ts;
+ LWLockRelease(&stats_shmem->lock);
+}
+
+void
+pgstat_vfdcache_snapshot_cb(void)
+{
+ PgStatShared_VfdCache *stats_shmem = &pgStatLocal.shmem->vfdcache;
+
+ LWLockAcquire(&stats_shmem->lock, LW_SHARED);
+ memcpy(&pgStatLocal.snapshot.vfdcache, &stats_shmem->stats,
+ sizeof(pgStatLocal.snapshot.vfdcache));
+ LWLockRelease(&stats_shmem->lock);
+}
+
+void
+pgstat_reset_vfdcache(void)
+{
+ pgstat_reset_of_kind(PGSTAT_KIND_VFDCACHE);
+}
diff --git a/src/backend/utils/adt/pgstatfuncs.c b/src/backend/utils/adt/pgstatfuncs.c
index 0d47d745c18..3499dd40700 100644
--- a/src/backend/utils/adt/pgstatfuncs.c
+++ b/src/backend/utils/adt/pgstatfuncs.c
@@ -26,6 +26,7 @@
#include "pgstat.h"
#include "postmaster/bgworker.h"
#include "replication/logicallauncher.h"
+#include "storage/fd.h"
#include "storage/proc.h"
#include "storage/procarray.h"
#include "utils/acl.h"
@@ -1398,6 +1399,47 @@ pg_stat_get_buf_alloc(PG_FUNCTION_ARGS)
PG_RETURN_INT64(pgstat_fetch_stat_bgwriter()->buf_alloc);
}
+Datum
+pg_stat_get_vfd_hits(PG_FUNCTION_ARGS)
+{
+ PG_RETURN_INT64(pgstat_fetch_stat_vfdcache()->vfd_hits);
+}
+
+Datum
+pg_stat_get_vfd_misses(PG_FUNCTION_ARGS)
+{
+ PG_RETURN_INT64(pgstat_fetch_stat_vfdcache()->vfd_misses);
+}
+
+Datum
+pg_stat_get_vfd_max_open_fds(PG_FUNCTION_ARGS)
+{
+ PG_RETURN_INT32(max_safe_fds);
+}
+
+Datum
+pg_stat_get_vfd_stat_reset_time(PG_FUNCTION_ARGS)
+{
+ TimestampTz ts = pgstat_fetch_stat_vfdcache()->stat_reset_timestamp;
+
+ if (ts == 0)
+ PG_RETURN_NULL();
+
+ PG_RETURN_TIMESTAMPTZ(ts);
+}
+
+/*
+ * pg_stat_reset_vfdcache
+ * Reset shared VFD cache counters.
+ */
+Datum
+pg_stat_reset_vfdcache(PG_FUNCTION_ARGS)
+{
+ pgstat_reset_vfdcache();
+ PG_RETURN_VOID();
+}
+
+
/*
* When adding a new column to the pg_stat_io view and the
* pg_stat_get_backend_io() function, add a new enum value here above
@@ -2099,6 +2141,7 @@ pg_stat_reset_shared(PG_FUNCTION_ARGS)
XLogPrefetchResetStats();
pgstat_reset_of_kind(PGSTAT_KIND_SLRU);
pgstat_reset_of_kind(PGSTAT_KIND_WAL);
+ pgstat_reset_of_kind(PGSTAT_KIND_VFDCACHE);
PG_RETURN_VOID();
}
@@ -2119,13 +2162,15 @@ pg_stat_reset_shared(PG_FUNCTION_ARGS)
XLogPrefetchResetStats();
else if (strcmp(target, "slru") == 0)
pgstat_reset_of_kind(PGSTAT_KIND_SLRU);
+ else if (strcmp(target, "vfdcache") == 0)
+ pgstat_reset_of_kind(PGSTAT_KIND_VFDCACHE);
else if (strcmp(target, "wal") == 0)
pgstat_reset_of_kind(PGSTAT_KIND_WAL);
else
ereport(ERROR,
(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
errmsg("unrecognized reset target: \"%s\"", target),
- errhint("Target must be \"archiver\", \"bgwriter\", \"checkpointer\", \"io\", \"lock\", \"recovery_prefetch\", \"slru\", or \"wal\".")));
+ errhint("Target must be \"archiver\", \"bgwriter\", \"checkpointer\", \"io\", \"lock\", \"recovery_prefetch\", \"slru\", \"vfdcache\", or \"wal\".")));
PG_RETURN_VOID();
}
diff --git a/src/include/catalog/pg_proc.dat b/src/include/catalog/pg_proc.dat
index 1d2a9db3262..d4ec44bf0f9 100644
--- a/src/include/catalog/pg_proc.dat
+++ b/src/include/catalog/pg_proc.dat
@@ -12775,5 +12775,35 @@
{ oid => '6462', descr => 'hash',
proname => 'hashoid8extended', prorettype => 'int8',
proargtypes => 'oid8 int8', prosrc => 'hashoid8extended' },
+{ oid => '9560',
+ descr => 'statistics: number of VFD cache hits',
+ proname => 'pg_stat_get_vfd_hits',
+ provolatile => 'v', proparallel => 'r',
+ prorettype => 'int8', proargtypes => '',
+ prosrc => 'pg_stat_get_vfd_hits' },
+{ oid => '9561',
+ descr => 'statistics: number of VFD cache misses',
+ proname => 'pg_stat_get_vfd_misses',
+ provolatile => 'v', proparallel => 'r',
+ prorettype => 'int8', proargtypes => '',
+ prosrc => 'pg_stat_get_vfd_misses' },
+{ oid => '9564',
+ descr => 'statistics: timestamp of last VFD cache stats reset',
+ proname => 'pg_stat_get_vfd_stat_reset_time',
+ provolatile => 'v', proparallel => 'r',
+ prorettype => 'timestamptz', proargtypes => '',
+ prosrc => 'pg_stat_get_vfd_stat_reset_time' },
+{ oid => '9565',
+ descr => 'statistics: reset shared VFD cache counters',
+ proname => 'pg_stat_reset_vfdcache',
+ provolatile => 'v', proparallel => 'r',
+ prorettype => 'void', proargtypes => '',
+ prosrc => 'pg_stat_reset_vfdcache' },
+{ oid => '9566',
+ descr => 'statistics: max number of file descriptors available to backend',
+ proname => 'pg_stat_get_vfd_max_open_fds',
+ provolatile => 'v', proparallel => 'r',
+ prorettype => 'int4', proargtypes => '',
+ prosrc => 'pg_stat_get_vfd_max_open_fds' },
]
diff --git a/src/include/pgstat.h b/src/include/pgstat.h
index 204782fd630..e8395664df2 100644
--- a/src/include/pgstat.h
+++ b/src/include/pgstat.h
@@ -305,6 +305,19 @@ typedef struct PgStat_CheckpointerStats
TimestampTz stat_reset_timestamp;
} PgStat_CheckpointerStats;
+/* ---------
+ * PgStat_VfdCacheStats Virtual File Descriptor cache statistics
+ *
+ * Tracks hit/miss events in the VFD cache (fd.c). These counters
+ * are accumulated in shared fixed stats and exposed by pg_stat_vfdcache.
+ * ---------
+ */
+typedef struct PgStat_VfdCacheStats
+{
+ PgStat_Counter vfd_hits; /* fd was open, no open() was needed */
+ PgStat_Counter vfd_misses; /* fd was VFD_CLOSED, open() was required */
+ TimestampTz stat_reset_timestamp;
+} PgStat_VfdCacheStats;
/*
* Types related to counting IO operations
@@ -666,6 +679,13 @@ extern PgStat_BgWriterStats *pgstat_fetch_stat_bgwriter(void);
extern void pgstat_report_checkpointer(void);
extern PgStat_CheckpointerStats *pgstat_fetch_stat_checkpointer(void);
+/*
+ * Functions in pgstat_vfdcache.c
+ */
+
+extern PgStat_VfdCacheStats *pgstat_fetch_stat_vfdcache(void);
+extern void pgstat_reset_vfdcache(void);
+extern void pgstat_count_vfd_access(bool hit);
/*
* Functions in pgstat_io.c
@@ -941,6 +961,12 @@ extern PGDLLIMPORT int pgstat_fetch_consistency;
/* updated directly by bgwriter and bufmgr */
extern PGDLLIMPORT PgStat_BgWriterStats PendingBgWriterStats;
+/*
+ * Variables in pgstat_vfdcache.c
+ */
+
+/* updated by VFD counting functions called from fd.c */
+extern PGDLLIMPORT PgStat_VfdCacheStats PendingVfdCacheStats;
/*
* Variables in pgstat_checkpointer.c
diff --git a/src/include/utils/pgstat_internal.h b/src/include/utils/pgstat_internal.h
index 14369e59a1c..e24a1c84c9f 100644
--- a/src/include/utils/pgstat_internal.h
+++ b/src/include/utils/pgstat_internal.h
@@ -296,7 +296,7 @@ typedef struct PgStat_KindInfo
/*
* For variable-numbered stats: flush pending stats. Required if pending
* data is used. See flush_static_cb when dealing with stats data that
- * that cannot use PgStat_EntryRef->pending.
+ * cannot use PgStat_EntryRef->pending.
*/
bool (*flush_pending_cb) (PgStat_EntryRef *sr, bool nowait);
@@ -486,6 +486,13 @@ typedef struct PgStatShared_Wal
PgStat_WalStats stats;
} PgStatShared_Wal;
+typedef struct PgStatShared_VfdCache
+{
+ /* lock protects ->stats */
+ LWLock lock;
+ PgStat_VfdCacheStats stats;
+} PgStatShared_VfdCache;
+
/* ----------
@@ -587,6 +594,7 @@ typedef struct PgStat_ShmemControl
PgStatShared_Lock lock;
PgStatShared_SLRU slru;
PgStatShared_Wal wal;
+ PgStatShared_VfdCache vfdcache;
/*
* Custom stats data with fixed-numbered objects, indexed by (PgStat_Kind
@@ -623,6 +631,8 @@ typedef struct PgStat_Snapshot
PgStat_WalStats wal;
+ PgStat_VfdCacheStats vfdcache;
+
/*
* Data in snapshot for custom fixed-numbered statistics, indexed by
* (PgStat_Kind - PGSTAT_KIND_CUSTOM_MIN). Each entry is allocated in
@@ -739,6 +749,16 @@ extern void pgstat_checkpointer_reset_all_cb(TimestampTz ts);
extern void pgstat_checkpointer_snapshot_cb(void);
+/*
+ * Functions in pgstat_vfdcache.c
+ */
+
+extern bool pgstat_vfdcache_flush_cb(bool nowait);
+extern void pgstat_vfdcache_init_shmem_cb(void *stats);
+extern void pgstat_vfdcache_reset_all_cb(TimestampTz ts);
+extern void pgstat_vfdcache_snapshot_cb(void);
+
+
/*
* Functions in pgstat_database.c
*/
diff --git a/src/include/utils/pgstat_kind.h b/src/include/utils/pgstat_kind.h
index 45ca599d0dd..d998a3fc091 100644
--- a/src/include/utils/pgstat_kind.h
+++ b/src/include/utils/pgstat_kind.h
@@ -40,9 +40,10 @@
#define PGSTAT_KIND_LOCK 12
#define PGSTAT_KIND_SLRU 13
#define PGSTAT_KIND_WAL 14
+#define PGSTAT_KIND_VFDCACHE 15
#define PGSTAT_KIND_BUILTIN_MIN PGSTAT_KIND_DATABASE
-#define PGSTAT_KIND_BUILTIN_MAX PGSTAT_KIND_WAL
+#define PGSTAT_KIND_BUILTIN_MAX PGSTAT_KIND_VFDCACHE
#define PGSTAT_KIND_BUILTIN_SIZE (PGSTAT_KIND_BUILTIN_MAX + 1)
/* Custom stats kinds */
diff --git a/src/test/regress/expected/rules.out b/src/test/regress/expected/rules.out
index 1a29d46213e..cdf21d82924 100644
--- a/src/test/regress/expected/rules.out
+++ b/src/test/regress/expected/rules.out
@@ -2426,6 +2426,14 @@ pg_stat_user_tables| SELECT relid,
stats_reset
FROM pg_stat_all_tables
WHERE ((schemaname <> ALL (ARRAY['pg_catalog'::name, 'information_schema'::name])) AND (schemaname !~ '^pg_toast'::text));
+pg_stat_vfdcache| SELECT pg_stat_get_vfd_hits() AS hits,
+ pg_stat_get_vfd_misses() AS misses,
+ pg_stat_get_vfd_max_open_fds() AS max_open_fds,
+ CASE
+ WHEN ((pg_stat_get_vfd_hits() + pg_stat_get_vfd_misses()) = 0) THEN NULL::double precision
+ ELSE ((pg_stat_get_vfd_hits())::double precision / ((pg_stat_get_vfd_hits() + pg_stat_get_vfd_misses()))::double precision)
+ END AS hit_ratio,
+ pg_stat_get_vfd_stat_reset_time() AS stats_reset;
pg_stat_wal| SELECT wal_records,
wal_fpi,
wal_bytes,
diff --git a/src/test/regress/expected/stats.out b/src/test/regress/expected/stats.out
index c682a9ed60a..91b9a79aeee 100644
--- a/src/test/regress/expected/stats.out
+++ b/src/test/regress/expected/stats.out
@@ -128,7 +128,8 @@ SELECT id, name, fixed_amount,
12 | lock | t | f | t
13 | slru | t | f | t
14 | wal | t | f | t
-(14 rows)
+ 15 | vfdcache | t | f | t
+(15 rows)
-- ensure that both seqscan and indexscan plans are allowed
SET enable_seqscan TO on;
@@ -1178,10 +1179,24 @@ SELECT stats_reset > :'wal_reset_ts'::timestamptz FROM pg_stat_wal;
t
(1 row)
+-- Test that reset_shared with vfdcache specified as the stats type works
+SELECT stats_reset AS vfdcache_reset_ts FROM pg_stat_vfdcache \gset
+SELECT pg_stat_reset_shared('vfdcache');
+ pg_stat_reset_shared
+----------------------
+
+(1 row)
+
+SELECT stats_reset > :'vfdcache_reset_ts'::timestamptz FROM pg_stat_vfdcache;
+ ?column?
+----------
+ t
+(1 row)
+
-- Test error case for reset_shared with unknown stats type
SELECT pg_stat_reset_shared('unknown');
ERROR: unrecognized reset target: "unknown"
-HINT: Target must be "archiver", "bgwriter", "checkpointer", "io", "lock", "recovery_prefetch", "slru", or "wal".
+HINT: Target must be "archiver", "bgwriter", "checkpointer", "io", "lock", "recovery_prefetch", "slru", "vfdcache", or "wal".
-- Test that reset works for pg_stat_database and pg_stat_database_conflicts
-- Since pg_stat_database stats_reset starts out as NULL, reset it once first so that we
-- have a baseline for comparison. The same for pg_stat_database_conflicts as it shares
diff --git a/src/test/regress/sql/stats.sql b/src/test/regress/sql/stats.sql
index d4623c32cd3..a4fa1ff7556 100644
--- a/src/test/regress/sql/stats.sql
+++ b/src/test/regress/sql/stats.sql
@@ -535,6 +535,11 @@ SELECT stats_reset AS wal_reset_ts FROM pg_stat_wal \gset
SELECT pg_stat_reset_shared('wal');
SELECT stats_reset > :'wal_reset_ts'::timestamptz FROM pg_stat_wal;
+-- Test that reset_shared with vfdcache specified as the stats type works
+SELECT stats_reset AS vfdcache_reset_ts FROM pg_stat_vfdcache \gset
+SELECT pg_stat_reset_shared('vfdcache');
+SELECT stats_reset > :'vfdcache_reset_ts'::timestamptz FROM pg_stat_vfdcache;
+
-- Test error case for reset_shared with unknown stats type
SELECT pg_stat_reset_shared('unknown');
--
2.34.1
From e76731a27c94c3341f46c95514267f5e7d07711e Mon Sep 17 00:00:00 2001
From: AyoubKAZ <[email protected]>
Date: Tue, 25 Aug 2026 00:46:42 +0200
Subject: [PATCH v5 2/2] Add VFD cache footprint metrics to pg_stat_vfdcache
Extend pg_stat_vfdcache with three additional columns:
open_entries number of currently open file descriptors inside VFD cache
allocated_entries total number of allocated slots in the cache
cache_bytes total memory used by VFD cache, including sizeof(Vfd) for
allocated slots and the heap-allocated fileName strings
These are live gauges. Each backend publishes its current VFD cache
footprint into backend shared stats during backend stats flush, and
SQL accessors sum those backend shared stats entries to produce
cluster-wide totals.
The memory footprint is computed incrementally inside fd.c using a
running counter, avoiding expensive iterations or averages, and
accurately accounting for filename string allocations.
---
doc/src/sgml/monitoring.sgml | 33 ++++++++
src/backend/catalog/system_views.sql | 3 +
src/backend/storage/file/fd.c | 48 ++++++++++-
src/backend/utils/activity/pgstat_backend.c | 52 ++++++++++++
src/backend/utils/adt/pgstatfuncs.c | 93 +++++++++++++++++++++
src/include/catalog/pg_proc.dat | 18 ++++
src/include/pgstat.h | 15 ++++
src/include/storage/fd.h | 3 +
src/include/utils/pgstat_internal.h | 6 +-
src/test/regress/expected/rules.out | 3 +
10 files changed, 272 insertions(+), 2 deletions(-)
diff --git a/doc/src/sgml/monitoring.sgml b/doc/src/sgml/monitoring.sgml
index d2997c4d090..14e92d9c4fa 100644
--- a/doc/src/sgml/monitoring.sgml
+++ b/doc/src/sgml/monitoring.sgml
@@ -3967,6 +3967,39 @@ description | Waiting for a newly initialized WAL file to reach durable storage
</para></entry>
</row>
+ <row>
+ <entry role="catalog_table_entry"><para role="column_definition">
+ <structfield>open_entries</structfield> <type>bigint</type>
+ </para>
+ <para>
+ Sum of VFD slots currently holding an open kernel file descriptor
+ across all active backends (equivalent to summing each backend's
+ <literal>nfile</literal> counter)
+ </para></entry>
+ </row>
+
+ <row>
+ <entry role="catalog_table_entry"><para role="column_definition">
+ <structfield>allocated_entries</structfield> <type>bigint</type>
+ </para>
+ <para>
+ Sum of allocated VFD cache entries across all active backends,
+ including entries whose file descriptor has been closed by the LRU
+ eviction policy but whose slot has not yet been freed
+ </para></entry>
+ </row>
+
+ <row>
+ <entry role="catalog_table_entry"><para role="column_definition">
+ <structfield>cache_bytes</structfield> <type>bigint</type>
+ </para>
+ <para>
+ Sum of memory used by VFD cache entries across all active backends,
+ in bytes; includes <literal>sizeof(Vfd)</literal> for each allocated
+ slot plus the heap-allocated file name string for each populated slot
+ </para></entry>
+ </row>
+
<row>
<entry role="catalog_table_entry"><para role="column_definition">
<structfield>max_open_fds</structfield> <type>integer</type>
diff --git a/src/backend/catalog/system_views.sql b/src/backend/catalog/system_views.sql
index 844fea1391f..2b5a92b1e70 100644
--- a/src/backend/catalog/system_views.sql
+++ b/src/backend/catalog/system_views.sql
@@ -1573,6 +1573,9 @@ CREATE VIEW pg_stat_vfdcache AS
SELECT
pg_stat_get_vfd_hits() AS hits,
pg_stat_get_vfd_misses() AS misses,
+ pg_stat_get_vfd_cache_open_entries() AS open_entries,
+ pg_stat_get_vfd_cache_allocated_entries() AS allocated_entries,
+ pg_stat_get_vfd_cache_bytes() AS cache_bytes,
pg_stat_get_vfd_max_open_fds() AS max_open_fds,
CASE
WHEN pg_stat_get_vfd_hits() + pg_stat_get_vfd_misses() = 0
diff --git a/src/backend/storage/file/fd.c b/src/backend/storage/file/fd.c
index d2436ed953e..f7c62024b62 100644
--- a/src/backend/storage/file/fd.c
+++ b/src/backend/storage/file/fd.c
@@ -225,6 +225,14 @@ static Size SizeVfdCache = 0;
*/
static int nfile = 0;
+/*
+ * Running total of memory used by the VFD cache for this backend,
+ * including sizeof(Vfd) for each allocated slot plus the malloc'd
+ * fileName string for each populated slot. Updated incrementally in
+ * AllocateVfd(), PathNameOpenFilePerm(), and FreeVfd().
+ */
+static uint64 VfdCacheFootprintBytes = 0;
+
/*
* Flag to tell whether it's worth scanning VfdCache looking for temp files
* to close
@@ -1444,8 +1452,10 @@ AllocateVfd(void)
VfdCache[0].nextFree = SizeVfdCache;
/*
- * Record the new size
+ * Record the new size and account for the newly allocated Vfd
+ * structs.
*/
+ VfdCacheFootprintBytes += (newCacheSize - SizeVfdCache) * sizeof(Vfd);
SizeVfdCache = newCacheSize;
}
@@ -1466,6 +1476,7 @@ FreeVfd(File file)
if (vfdP->fileName != NULL)
{
+ VfdCacheFootprintBytes -= strlen(vfdP->fileName) + 1;
free(vfdP->fileName);
vfdP->fileName = NULL;
}
@@ -1512,6 +1523,40 @@ FileAccess(File file)
return 0;
}
+/*
+ * Return the number of VFD slots currently holding an open file descriptor.
+ * This is the nfile counter, which tracks FDs actually open in the kernel.
+ */
+uint64
+GetVfdCacheOpenEntries(void)
+{
+ return (uint64) nfile;
+}
+
+/*
+ * Return the number of currently allocated VFD entries for this backend,
+ * excluding slot 0 which is used as freelist/LRU header.
+ */
+uint64
+GetVfdCacheAllocatedEntries(void)
+{
+ if (SizeVfdCache == 0)
+ return 0;
+
+ return (uint64) (SizeVfdCache - 1);
+}
+
+/*
+ * Return the current memory footprint of the VFD cache for this backend.
+ * This includes sizeof(Vfd) for each allocated slot and the malloc'd
+ * fileName bytes for each currently-populated slot.
+ */
+uint64
+GetVfdCacheBytes(void)
+{
+ return VfdCacheFootprintBytes;
+}
+
/*
* Called whenever a temporary file is deleted to report its size.
*/
@@ -1624,6 +1669,7 @@ PathNameOpenFilePerm(const char *fileName, int fileFlags, mode_t fileMode)
vfdP->fd));
vfdP->fileName = fnamecopy;
+ VfdCacheFootprintBytes += strlen(fnamecopy) + 1;
/* Saved flags are adjusted to be OK for re-opening file */
vfdP->fileFlags = fileFlags & ~(O_CREAT | O_TRUNC | O_EXCL);
vfdP->fileMode = fileMode;
diff --git a/src/backend/utils/activity/pgstat_backend.c b/src/backend/utils/activity/pgstat_backend.c
index b736b2ccc6f..a493b559911 100644
--- a/src/backend/utils/activity/pgstat_backend.c
+++ b/src/backend/utils/activity/pgstat_backend.c
@@ -27,6 +27,7 @@
#include "access/xlog.h"
#include "executor/instrument.h"
#include "storage/bufmgr.h"
+#include "storage/fd.h"
#include "storage/proc.h"
#include "storage/procarray.h"
#include "utils/memutils.h"
@@ -49,6 +50,12 @@ static bool backend_has_lockstats = false;
*/
static WalUsage prevBackendWalUsage;
+/*
+ * Last per-backend VFD cache gauges published to backend stats.
+ * Used to detect whether anything changed since the last flush.
+ */
+static PgStat_BackendVfdCacheStats prevBackendVfdCacheStats;
+
/*
* Utility routines to report I/O stats for backends, kept here to avoid
* exposing PendingBackendStats to the outside world.
@@ -253,6 +260,21 @@ pgstat_backend_wal_have_pending(void)
return (pgWalUsage.wal_records != prevBackendWalUsage.wal_records);
}
+/*
+ * Determine whether VFD cache gauges have changed since the last flush.
+ */
+static inline bool
+pgstat_backend_vfdcache_have_pending(void)
+{
+ PgStat_Counter cur_open = (PgStat_Counter) GetVfdCacheOpenEntries();
+ PgStat_Counter cur_alloc = (PgStat_Counter) GetVfdCacheAllocatedEntries();
+ PgStat_Counter cur_bytes = (PgStat_Counter) GetVfdCacheBytes();
+
+ return cur_open != prevBackendVfdCacheStats.open_entries ||
+ cur_alloc != prevBackendVfdCacheStats.allocated_entries ||
+ cur_bytes != prevBackendVfdCacheStats.cache_bytes;
+}
+
/*
* Flush out locally pending backend WAL statistics. Locking is managed
* by the caller.
@@ -326,6 +348,27 @@ pgstat_flush_backend_entry_lock(PgStat_EntryRef *entry_ref)
backend_has_lockstats = false;
}
+/*
+ * Flush out locally pending backend VFD cache gauges. Locking is managed
+ * by the caller. No need to check for pending data here; the caller does
+ * that before acquiring the lock.
+ */
+static void
+pgstat_flush_backend_entry_vfdcache(PgStat_EntryRef *entry_ref)
+{
+ PgStatShared_Backend *shbackendent;
+ PgStat_BackendVfdCacheStats *bktype_shstats;
+
+ shbackendent = (PgStatShared_Backend *) entry_ref->shared_stats;
+ bktype_shstats = &shbackendent->stats.vfdcache_stats;
+
+ bktype_shstats->open_entries = (PgStat_Counter) GetVfdCacheOpenEntries();
+ bktype_shstats->allocated_entries = (PgStat_Counter) GetVfdCacheAllocatedEntries();
+ bktype_shstats->cache_bytes = (PgStat_Counter) GetVfdCacheBytes();
+
+ prevBackendVfdCacheStats = *bktype_shstats;
+}
+
/*
* Flush out locally pending backend statistics
*
@@ -354,6 +397,11 @@ pgstat_flush_backend(bool nowait, uint32 flags)
if ((flags & PGSTAT_BACKEND_FLUSH_LOCK) && backend_has_lockstats)
has_pending_data = true;
+ /* Some VFD cache data pending? */
+ if ((flags & PGSTAT_BACKEND_FLUSH_VFDCACHE) &&
+ pgstat_backend_vfdcache_have_pending())
+ has_pending_data = true;
+
if (!has_pending_data)
return false;
@@ -372,6 +420,9 @@ pgstat_flush_backend(bool nowait, uint32 flags)
if (flags & PGSTAT_BACKEND_FLUSH_LOCK)
pgstat_flush_backend_entry_lock(entry_ref);
+ if (flags & PGSTAT_BACKEND_FLUSH_VFDCACHE)
+ pgstat_flush_backend_entry_vfdcache(entry_ref);
+
pgstat_unlock_entry(entry_ref);
return false;
@@ -411,6 +462,7 @@ pgstat_create_backend(ProcNumber procnum)
MemSet(&PendingBackendStats, 0, sizeof(PgStat_BackendPending));
backend_has_iostats = false;
backend_has_lockstats = false;
+ MemSet(&prevBackendVfdCacheStats, 0, sizeof(prevBackendVfdCacheStats));
/*
* Initialize prevBackendWalUsage with pgWalUsage so that
diff --git a/src/backend/utils/adt/pgstatfuncs.c b/src/backend/utils/adt/pgstatfuncs.c
index 3499dd40700..aa6b16f38c4 100644
--- a/src/backend/utils/adt/pgstatfuncs.c
+++ b/src/backend/utils/adt/pgstatfuncs.c
@@ -15,6 +15,7 @@
#include "postgres.h"
#include "access/htup_details.h"
+#include "access/xact.h"
#include "access/xlog.h"
#include "access/xlogprefetcher.h"
#include "catalog/catalog.h"
@@ -1411,6 +1412,98 @@ pg_stat_get_vfd_misses(PG_FUNCTION_ARGS)
PG_RETURN_INT64(pgstat_fetch_stat_vfdcache()->vfd_misses);
}
+/*
+ * Sum per-backend VFD cache gauges across all currently active backends.
+ * Results are cached for the duration of the current SQL statement to
+ * avoid redundant scans when the view calls multiple getter functions.
+ */
+static void
+pgstat_get_vfd_backend_sums(PgStat_Counter *open_sum,
+ PgStat_Counter *alloc_sum,
+ PgStat_Counter *bytes_sum)
+{
+ static TimestampTz cached_stmt_start_ts = 0;
+ static PgStat_Counter cached_open_sum = 0;
+ static PgStat_Counter cached_alloc_sum = 0;
+ static PgStat_Counter cached_bytes_sum = 0;
+ TimestampTz stmt_start_ts = GetCurrentStatementStartTimestamp();
+ int num_backends = pgstat_fetch_stat_numbackends();
+
+ if (cached_stmt_start_ts == stmt_start_ts)
+ {
+ *open_sum = cached_open_sum;
+ *alloc_sum = cached_alloc_sum;
+ *bytes_sum = cached_bytes_sum;
+ return;
+ }
+
+ *open_sum = 0;
+ *alloc_sum = 0;
+ *bytes_sum = 0;
+
+ for (int curr_backend = 1; curr_backend <= num_backends; curr_backend++)
+ {
+ LocalPgBackendStatus *local_beentry;
+ PgBackendStatus *beentry;
+ PgStat_Backend *backend_stats;
+
+ local_beentry = pgstat_get_local_beentry_by_index(curr_backend);
+ beentry = &local_beentry->backendStatus;
+
+ if (!pgstat_tracks_backend_bktype(beentry->st_backendType))
+ continue;
+
+ backend_stats = pgstat_fetch_stat_backend(local_beentry->proc_number);
+ if (!backend_stats)
+ continue;
+
+ *open_sum += backend_stats->vfdcache_stats.open_entries;
+ *alloc_sum += backend_stats->vfdcache_stats.allocated_entries;
+ *bytes_sum += backend_stats->vfdcache_stats.cache_bytes;
+ }
+
+ cached_open_sum = *open_sum;
+ cached_alloc_sum = *alloc_sum;
+ cached_bytes_sum = *bytes_sum;
+ cached_stmt_start_ts = stmt_start_ts;
+}
+
+Datum
+pg_stat_get_vfd_cache_open_entries(PG_FUNCTION_ARGS)
+{
+ PgStat_Counter open_sum;
+ PgStat_Counter alloc_sum;
+ PgStat_Counter bytes_sum;
+
+ pgstat_get_vfd_backend_sums(&open_sum, &alloc_sum, &bytes_sum);
+
+ PG_RETURN_INT64(open_sum);
+}
+
+Datum
+pg_stat_get_vfd_cache_allocated_entries(PG_FUNCTION_ARGS)
+{
+ PgStat_Counter open_sum;
+ PgStat_Counter alloc_sum;
+ PgStat_Counter bytes_sum;
+
+ pgstat_get_vfd_backend_sums(&open_sum, &alloc_sum, &bytes_sum);
+
+ PG_RETURN_INT64(alloc_sum);
+}
+
+Datum
+pg_stat_get_vfd_cache_bytes(PG_FUNCTION_ARGS)
+{
+ PgStat_Counter open_sum;
+ PgStat_Counter alloc_sum;
+ PgStat_Counter bytes_sum;
+
+ pgstat_get_vfd_backend_sums(&open_sum, &alloc_sum, &bytes_sum);
+
+ PG_RETURN_INT64(bytes_sum);
+}
+
Datum
pg_stat_get_vfd_max_open_fds(PG_FUNCTION_ARGS)
{
diff --git a/src/include/catalog/pg_proc.dat b/src/include/catalog/pg_proc.dat
index d4ec44bf0f9..68d0b8a4fc3 100644
--- a/src/include/catalog/pg_proc.dat
+++ b/src/include/catalog/pg_proc.dat
@@ -12805,5 +12805,23 @@
provolatile => 'v', proparallel => 'r',
prorettype => 'int4', proargtypes => '',
prosrc => 'pg_stat_get_vfd_max_open_fds' },
+{ oid => '9562',
+ descr => 'statistics: number of VFD slots with an open file descriptor across backends',
+ proname => 'pg_stat_get_vfd_cache_open_entries',
+ provolatile => 'v', proparallel => 'r',
+ prorettype => 'int8', proargtypes => '',
+ prosrc => 'pg_stat_get_vfd_cache_open_entries' },
+{ oid => '9563',
+ descr => 'statistics: total number of allocated VFD cache entries across backends',
+ proname => 'pg_stat_get_vfd_cache_allocated_entries',
+ provolatile => 'v', proparallel => 'r',
+ prorettype => 'int8', proargtypes => '',
+ prosrc => 'pg_stat_get_vfd_cache_allocated_entries' },
+{ oid => '9567',
+ descr => 'statistics: total memory footprint of VFD cache across backends in bytes',
+ proname => 'pg_stat_get_vfd_cache_bytes',
+ provolatile => 'v', proparallel => 'r',
+ prorettype => 'int8', proargtypes => '',
+ prosrc => 'pg_stat_get_vfd_cache_bytes' },
]
diff --git a/src/include/pgstat.h b/src/include/pgstat.h
index e8395664df2..73cd735de06 100644
--- a/src/include/pgstat.h
+++ b/src/include/pgstat.h
@@ -319,6 +319,20 @@ typedef struct PgStat_VfdCacheStats
TimestampTz stat_reset_timestamp;
} PgStat_VfdCacheStats;
+/* -------
+ * PgStat_BackendVfdCacheStats Per-backend VFD cache gauges
+ *
+ * These are live gauges (not cumulative counters) snapshotted from each
+ * backend's fd.c variables during stats flush.
+ * -------
+ */
+typedef struct PgStat_BackendVfdCacheStats
+{
+ PgStat_Counter open_entries; /* FDs currently open (= nfile) */
+ PgStat_Counter allocated_entries; /* total allocated VFD slots */
+ PgStat_Counter cache_bytes; /* memory footprint in bytes */
+} PgStat_BackendVfdCacheStats;
+
/*
* Types related to counting IO operations
*/
@@ -584,6 +598,7 @@ typedef struct PgStat_Backend
PgStat_BktypeIO io_stats;
PgStat_WalCounters wal_counters;
PgStat_PendingLock lock_stats;
+ PgStat_BackendVfdCacheStats vfdcache_stats;
} PgStat_Backend;
/* ---------
diff --git a/src/include/storage/fd.h b/src/include/storage/fd.h
index 8ac466fd346..672e18ca19e 100644
--- a/src/include/storage/fd.h
+++ b/src/include/storage/fd.h
@@ -149,6 +149,9 @@ extern char *FilePathName(File file);
extern int FileGetRawDesc(File file);
extern int FileGetRawFlags(File file);
extern mode_t FileGetRawMode(File file);
+extern uint64 GetVfdCacheOpenEntries(void);
+extern uint64 GetVfdCacheAllocatedEntries(void);
+extern uint64 GetVfdCacheBytes(void);
/* Operations used for sharing named temporary files */
extern File PathNameCreateTemporaryFile(const char *path, bool error_on_failure);
diff --git a/src/include/utils/pgstat_internal.h b/src/include/utils/pgstat_internal.h
index e24a1c84c9f..8b08990cc1b 100644
--- a/src/include/utils/pgstat_internal.h
+++ b/src/include/utils/pgstat_internal.h
@@ -724,7 +724,11 @@ extern void pgstat_archiver_snapshot_cb(void);
#define PGSTAT_BACKEND_FLUSH_IO (1 << 0) /* Flush I/O statistics */
#define PGSTAT_BACKEND_FLUSH_WAL (1 << 1) /* Flush WAL statistics */
#define PGSTAT_BACKEND_FLUSH_LOCK (1 << 2) /* Flush lock statistics */
-#define PGSTAT_BACKEND_FLUSH_ALL (PGSTAT_BACKEND_FLUSH_IO | PGSTAT_BACKEND_FLUSH_WAL | PGSTAT_BACKEND_FLUSH_LOCK)
+#define PGSTAT_BACKEND_FLUSH_VFDCACHE (1 << 3) /* Flush VFD cache gauges */
+#define PGSTAT_BACKEND_FLUSH_ALL (PGSTAT_BACKEND_FLUSH_IO | \
+ PGSTAT_BACKEND_FLUSH_WAL | \
+ PGSTAT_BACKEND_FLUSH_LOCK | \
+ PGSTAT_BACKEND_FLUSH_VFDCACHE)
extern bool pgstat_flush_backend(bool nowait, uint32 flags);
extern bool pgstat_backend_flush_cb(bool nowait);
diff --git a/src/test/regress/expected/rules.out b/src/test/regress/expected/rules.out
index cdf21d82924..3d38a1bf6b8 100644
--- a/src/test/regress/expected/rules.out
+++ b/src/test/regress/expected/rules.out
@@ -2428,6 +2428,9 @@ pg_stat_user_tables| SELECT relid,
WHERE ((schemaname <> ALL (ARRAY['pg_catalog'::name, 'information_schema'::name])) AND (schemaname !~ '^pg_toast'::text));
pg_stat_vfdcache| SELECT pg_stat_get_vfd_hits() AS hits,
pg_stat_get_vfd_misses() AS misses,
+ pg_stat_get_vfd_cache_open_entries() AS open_entries,
+ pg_stat_get_vfd_cache_allocated_entries() AS allocated_entries,
+ pg_stat_get_vfd_cache_bytes() AS cache_bytes,
pg_stat_get_vfd_max_open_fds() AS max_open_fds,
CASE
WHEN ((pg_stat_get_vfd_hits() + pg_stat_get_vfd_misses()) = 0) THEN NULL::double precision
--
2.34.1
