From fcd68e8ddd702d8926d24b8cc0a2335550d58e50 Mon Sep 17 00:00:00 2001 From: Alena Rybakina Date: Mon, 16 Mar 2026 01:55:22 +0300 Subject: [PATCH] Track table VM stability. Add visible_pages_vm_cleared and frozen_pages_vm_cleared counters to pg_stat_all_tables tracking the number of times the all-visible and all-frozen bits are cleared in the visibility map. These bits are cleared by backend processes during regular DML operations. Hence, the counters are placed in table statistic entry. A high visible_pages_vm_cleared rate relative to DML volume indicates that modifications are scattered across previously-clean pages rather than concentrated on already-dirty ones, causing index-only scans to fall back to heap fetches. A high rev_all_frozen_pages rate indicates that vacuum's freezing work is being frequently undone by concurrent DML. Authors: Alena Rybakina , Andrei Lepikhov , Andrei Zubkov Reviewed-by: Dilip Kumar , Masahiko Sawada , Ilia Evdokimov , Jian He , Kirill Reshke , Alexander Korotkov , Jim Nasby , Sami Imseih , Karina Litskevich , Andrey Borodin --- doc/src/sgml/monitoring.sgml | 32 ++++++++++++++ src/backend/access/heap/visibilitymap.c | 10 +++++ src/backend/catalog/system_views.sql | 4 +- src/backend/utils/activity/pgstat_relation.c | 2 + src/backend/utils/adt/pgstatfuncs.c | 6 +++ src/include/catalog/pg_proc.dat | 10 +++++ src/include/pgstat.h | 17 +++++++- src/test/regress/expected/rules.out | 12 ++++-- src/test/regress/expected/vacuum.out | 45 ++++++++++++++++++++ src/test/regress/sql/vacuum.sql | 21 +++++++++ 10 files changed, 154 insertions(+), 5 deletions(-) diff --git a/doc/src/sgml/monitoring.sgml b/doc/src/sgml/monitoring.sgml index 9c5c6dc490f..0ec4ddbd6ee 100644 --- a/doc/src/sgml/monitoring.sgml +++ b/doc/src/sgml/monitoring.sgml @@ -4258,6 +4258,38 @@ description | Waiting for a newly initialized WAL file to reach durable storage + + + visible_pages_vm_cleared bigint + + + Number of times the all-visible bit in the + visibility map was cleared for a + page of this table. The all-visible bit is cleared by backend + processes when they modify a heap page that was previously marked + all-visible, for example during an INSERT, + UPDATE, or DELETE. + A high rate of change in this counter means that index-only scans + on this table may frequently need to fall back to heap fetches, + and that vacuum must re-do visibility map work on those pages. + + + + + + frozen_pages_vm_cleared bigint + + + Number of times the all-frozen bit in the + visibility map was cleared for a + page of this table. The all-frozen bit is cleared by backend + processes when they modify a heap page that was previously marked + all-frozen. A high value compared to the number of vacuum cycles + indicates that DML activity is frequently undoing the freezing work + performed by vacuum. + + + last_vacuum timestamp with time zone diff --git a/src/backend/access/heap/visibilitymap.c b/src/backend/access/heap/visibilitymap.c index e21b96281a6..11a98482743 100644 --- a/src/backend/access/heap/visibilitymap.c +++ b/src/backend/access/heap/visibilitymap.c @@ -92,6 +92,7 @@ #include "access/xloginsert.h" #include "access/xlogutils.h" #include "miscadmin.h" +#include "pgstat.h" #include "port/pg_bitutils.h" #include "storage/bufmgr.h" #include "storage/smgr.h" @@ -163,6 +164,15 @@ visibilitymap_clear(Relation rel, BlockNumber heapBlk, Buffer vmbuf, uint8 flags if (map[mapByte] & mask) { + /* + * Track how often all-visible or all-frozen bits are cleared in the + * visibility map. + */ + if (map[mapByte] & ((flags & VISIBILITYMAP_ALL_VISIBLE) << mapOffset)) + pgstat_count_vm_rev_all_visible(rel); + if (map[mapByte] & ((flags & VISIBILITYMAP_ALL_FROZEN) << mapOffset)) + pgstat_count_vm_rev_all_frozen(rel); + map[mapByte] &= ~mask; MarkBufferDirty(vmbuf); diff --git a/src/backend/catalog/system_views.sql b/src/backend/catalog/system_views.sql index 90d48bc9c80..9f8645e4fa7 100644 --- a/src/backend/catalog/system_views.sql +++ b/src/backend/catalog/system_views.sql @@ -741,7 +741,9 @@ CREATE VIEW pg_stat_all_tables AS pg_stat_get_total_autovacuum_time(C.oid) AS total_autovacuum_time, pg_stat_get_total_analyze_time(C.oid) AS total_analyze_time, pg_stat_get_total_autoanalyze_time(C.oid) AS total_autoanalyze_time, - pg_stat_get_stat_reset_time(C.oid) AS stats_reset + pg_stat_get_stat_reset_time(C.oid) AS stats_reset, + pg_stat_get_visible_pages_vm_cleared(C.oid) AS visible_pages_vm_cleared, + pg_stat_get_frozen_pages_vm_cleared(C.oid) AS frozen_pages_vm_cleared FROM pg_class C LEFT JOIN pg_index I ON C.oid = I.indrelid LEFT JOIN pg_namespace N ON (N.oid = C.relnamespace) diff --git a/src/backend/utils/activity/pgstat_relation.c b/src/backend/utils/activity/pgstat_relation.c index bc8c43b96aa..c8dc61ac341 100644 --- a/src/backend/utils/activity/pgstat_relation.c +++ b/src/backend/utils/activity/pgstat_relation.c @@ -879,6 +879,8 @@ pgstat_relation_flush_cb(PgStat_EntryRef *entry_ref, bool nowait) tabentry->blocks_fetched += lstats->counts.blocks_fetched; tabentry->blocks_hit += lstats->counts.blocks_hit; + tabentry->visible_pages_vm_cleared += lstats->counts.visible_pages_vm_cleared; + tabentry->frozen_pages_vm_cleared += lstats->counts.frozen_pages_vm_cleared; /* Clamp live_tuples in case of negative delta_live_tuples */ tabentry->live_tuples = Max(tabentry->live_tuples, 0); diff --git a/src/backend/utils/adt/pgstatfuncs.c b/src/backend/utils/adt/pgstatfuncs.c index 5ac022274a7..b944851c240 100644 --- a/src/backend/utils/adt/pgstatfuncs.c +++ b/src/backend/utils/adt/pgstatfuncs.c @@ -107,6 +107,12 @@ PG_STAT_GET_RELENTRY_INT64(tuples_updated) /* pg_stat_get_vacuum_count */ PG_STAT_GET_RELENTRY_INT64(vacuum_count) +/* pg_stat_get_visible_pages_vm_cleared */ +PG_STAT_GET_RELENTRY_INT64(visible_pages_vm_cleared) + +/* pg_stat_get_frozen_pages_vm_cleared */ +PG_STAT_GET_RELENTRY_INT64(frozen_pages_vm_cleared) + #define PG_STAT_GET_RELENTRY_FLOAT8(stat) \ Datum \ CppConcat(pg_stat_get_,stat)(PG_FUNCTION_ARGS) \ diff --git a/src/include/catalog/pg_proc.dat b/src/include/catalog/pg_proc.dat index 361e2cfffeb..14e4a3c81e1 100644 --- a/src/include/catalog/pg_proc.dat +++ b/src/include/catalog/pg_proc.dat @@ -12833,4 +12833,14 @@ proname => 'hashoid8extended', prorettype => 'int8', proargtypes => 'oid8 int8', prosrc => 'hashoid8extended' }, +{ oid => '8002', + descr => 'statistics: number of times the all-visible pages in the visibility map were cleared for pages of this table', + proname => 'pg_stat_get_visible_pages_vm_cleared', provolatile => 's', + proparallel => 'r', prorettype => 'int8', proargtypes => 'oid', + prosrc => 'pg_stat_get_visible_pages_vm_cleared' }, +{ oid => '8003', + descr => 'statistics: number of times the all-frozen pages in the visibility map were cleared for pages of this table', + proname => 'pg_stat_get_frozen_pages_vm_cleared', provolatile => 's', + proparallel => 'r', prorettype => 'int8', proargtypes => 'oid', + prosrc => 'pg_stat_get_frozen_pages_vm_cleared' }, ] diff --git a/src/include/pgstat.h b/src/include/pgstat.h index 216b93492ba..70c1c8a41cf 100644 --- a/src/include/pgstat.h +++ b/src/include/pgstat.h @@ -159,6 +159,8 @@ typedef struct PgStat_TableCounts PgStat_Counter blocks_fetched; PgStat_Counter blocks_hit; + PgStat_Counter visible_pages_vm_cleared; + PgStat_Counter frozen_pages_vm_cleared; } PgStat_TableCounts; /* ---------- @@ -217,7 +219,7 @@ typedef struct PgStat_TableXactStatus * ------------------------------------------------------------ */ -#define PGSTAT_FILE_FORMAT_ID 0x01A5BCBB +#define PGSTAT_FILE_FORMAT_ID 0x01A5BCBC typedef struct PgStat_ArchiverStats { @@ -450,6 +452,8 @@ typedef struct PgStat_StatTabEntry PgStat_Counter blocks_fetched; PgStat_Counter blocks_hit; + PgStat_Counter visible_pages_vm_cleared; + PgStat_Counter frozen_pages_vm_cleared; TimestampTz last_vacuum_time; /* user initiated vacuum */ PgStat_Counter vacuum_count; @@ -725,6 +729,17 @@ extern void pgstat_report_analyze(Relation rel, if (pgstat_should_count_relation(rel)) \ (rel)->pgstat_info->counts.blocks_hit++; \ } while (0) +/* count revocations of all-visible and all-frozen bits in visibility map */ +#define pgstat_count_vm_rev_all_visible(rel) \ + do { \ + if (pgstat_should_count_relation(rel)) \ + (rel)->pgstat_info->counts.visible_pages_vm_cleared++; \ + } while (0) +#define pgstat_count_vm_rev_all_frozen(rel) \ + do { \ + if (pgstat_should_count_relation(rel)) \ + (rel)->pgstat_info->counts.frozen_pages_vm_cleared++; \ + } while (0) extern void pgstat_count_heap_insert(Relation rel, PgStat_Counter n); extern void pgstat_count_heap_update(Relation rel, bool hot, bool newpage); diff --git a/src/test/regress/expected/rules.out b/src/test/regress/expected/rules.out index 71d7262049e..704806b770a 100644 --- a/src/test/regress/expected/rules.out +++ b/src/test/regress/expected/rules.out @@ -1846,7 +1846,9 @@ pg_stat_all_tables| SELECT c.oid AS relid, pg_stat_get_total_autovacuum_time(c.oid) AS total_autovacuum_time, pg_stat_get_total_analyze_time(c.oid) AS total_analyze_time, pg_stat_get_total_autoanalyze_time(c.oid) AS total_autoanalyze_time, - pg_stat_get_stat_reset_time(c.oid) AS stats_reset + pg_stat_get_stat_reset_time(c.oid) AS stats_reset, + pg_stat_get_visible_pages_vm_cleared(c.oid) AS visible_pages_vm_cleared, + pg_stat_get_frozen_pages_vm_cleared(c.oid) AS frozen_pages_vm_cleared FROM ((pg_class c LEFT JOIN pg_index i ON ((c.oid = i.indrelid))) LEFT JOIN pg_namespace n ON ((n.oid = c.relnamespace))) @@ -2298,7 +2300,9 @@ pg_stat_sys_tables| SELECT relid, total_autovacuum_time, total_analyze_time, total_autoanalyze_time, - stats_reset + stats_reset, + visible_pages_vm_cleared, + frozen_pages_vm_cleared FROM pg_stat_all_tables WHERE ((schemaname = ANY (ARRAY['pg_catalog'::name, 'information_schema'::name])) OR (schemaname ~ '^pg_toast'::text)); pg_stat_user_functions| SELECT p.oid AS funcid, @@ -2353,7 +2357,9 @@ pg_stat_user_tables| SELECT relid, total_autovacuum_time, total_analyze_time, total_autoanalyze_time, - stats_reset + stats_reset, + visible_pages_vm_cleared, + frozen_pages_vm_cleared FROM pg_stat_all_tables WHERE ((schemaname <> ALL (ARRAY['pg_catalog'::name, 'information_schema'::name])) AND (schemaname !~ '^pg_toast'::text)); pg_stat_wal| SELECT wal_records, diff --git a/src/test/regress/expected/vacuum.out b/src/test/regress/expected/vacuum.out index d4696bc3325..5b2c44a8a1a 100644 --- a/src/test/regress/expected/vacuum.out +++ b/src/test/regress/expected/vacuum.out @@ -730,3 +730,48 @@ SELECT pg_column_toast_chunk_id(f1) = :'id_2_chunk' AS same_chunk (1 row) DROP TABLE vac_rewrite_toast; +-- Visibility map clear statistics: all_visible/all_frozen bits and vm_cleared counters +SET vacuum_freeze_min_age = 0; +SET vacuum_freeze_table_age = 0; +CREATE TABLE vacvm_clear_test (x int) + WITH (autovacuum_enabled = off, fillfactor = 70); +INSERT INTO vacvm_clear_test SELECT x FROM generate_series(1, 5000) AS g(x); +ANALYZE vacvm_clear_test; +SELECT pg_stat_force_next_flush(); + pg_stat_force_next_flush +-------------------------- + +(1 row) + +VACUUM vacvm_clear_test; +SELECT relallvisible > 0 AS all_visible, relallfrozen > 0 AS all_frozen + FROM pg_class WHERE relname = 'vacvm_clear_test'; + all_visible | all_frozen +-------------+------------ + t | t +(1 row) + +SELECT visible_pages_vm_cleared = 0 AS visible_pages_vm_cleared, frozen_pages_vm_cleared = 0 AS frozen_pages_vm_cleared + FROM pg_stat_all_tables WHERE relname = 'vacvm_clear_test'; + visible_pages_vm_cleared | frozen_pages_vm_cleared +--------------------------+------------------------- + t | t +(1 row) + +UPDATE vacvm_clear_test SET x = x + 1001; +SELECT pg_stat_force_next_flush(); + pg_stat_force_next_flush +-------------------------- + +(1 row) + +SELECT visible_pages_vm_cleared > 0 AS visible_pages_vm_cleared, frozen_pages_vm_cleared > 0 AS frozen_pages_vm_cleared + FROM pg_stat_all_tables WHERE relname = 'vacvm_clear_test'; + visible_pages_vm_cleared | frozen_pages_vm_cleared +--------------------------+------------------------- + t | t +(1 row) + +DROP TABLE vacvm_clear_test; +RESET vacuum_freeze_min_age; +RESET vacuum_freeze_table_age; diff --git a/src/test/regress/sql/vacuum.sql b/src/test/regress/sql/vacuum.sql index 247b8e23b23..2ffb6fe4c0d 100644 --- a/src/test/regress/sql/vacuum.sql +++ b/src/test/regress/sql/vacuum.sql @@ -525,3 +525,24 @@ SELECT id, pg_column_toast_chunk_id(f1) IS NULL AS f1_chunk_null, SELECT pg_column_toast_chunk_id(f1) = :'id_2_chunk' AS same_chunk FROM vac_rewrite_toast WHERE id = 2; DROP TABLE vac_rewrite_toast; + +-- Visibility map clear statistics: all_visible/all_frozen bits and vm_cleared counters +SET vacuum_freeze_min_age = 0; +SET vacuum_freeze_table_age = 0; +CREATE TABLE vacvm_clear_test (x int) + WITH (autovacuum_enabled = off, fillfactor = 70); +INSERT INTO vacvm_clear_test SELECT x FROM generate_series(1, 5000) AS g(x); +ANALYZE vacvm_clear_test; +SELECT pg_stat_force_next_flush(); +VACUUM vacvm_clear_test; +SELECT relallvisible > 0 AS all_visible, relallfrozen > 0 AS all_frozen + FROM pg_class WHERE relname = 'vacvm_clear_test'; +SELECT visible_pages_vm_cleared = 0 AS visible_pages_vm_cleared, frozen_pages_vm_cleared = 0 AS frozen_pages_vm_cleared + FROM pg_stat_all_tables WHERE relname = 'vacvm_clear_test'; +UPDATE vacvm_clear_test SET x = x + 1001; +SELECT pg_stat_force_next_flush(); +SELECT visible_pages_vm_cleared > 0 AS visible_pages_vm_cleared, frozen_pages_vm_cleared > 0 AS frozen_pages_vm_cleared + FROM pg_stat_all_tables WHERE relname = 'vacvm_clear_test'; +DROP TABLE vacvm_clear_test; +RESET vacuum_freeze_min_age; +RESET vacuum_freeze_table_age; -- 2.39.5 (Apple Git-154)