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help / color / mirror / Atom feedFrom: Bertrand Drouvot <[email protected]>
Subject: [PATCH v1 1/3] Add pgstat_report_anytime_stat() for periodic stats flushing
Date: Mon, 5 Jan 2026 09:41:39 +0000
Long running transactions can accumulate significant statistics (WAL, IO, ...)
that remain unflushed until the transaction ends. This delays visibility of
resource usage in monitoring views like pg_stat_io and pg_stat_wal.
This commit introduces pgstat_report_anytime_stat(), which flushes
non transactional statistics even inside active transactions. A new timeout
handler fires every second to call this function, ensuring timely stats visibility
without waiting for transaction completion.
Implementation details:
- Add PgStat_FlushBehavior enum to classify stats kinds:
* FLUSH_ANYTIME: Stats that can always be flushed (WAL, IO, ...)
* FLUSH_AT_TXN_BOUNDARY: Stats requiring transaction boundaries
- Modify pgstat_flush_pending_entries() and pgstat_flush_fixed_stats()
to accept a boolean anytime_only parameter:
* When false: flushes all stats (existing behavior)
* When true: flushes only FLUSH_ANYTIME stats and skips FLUSH_AT_TXN_BOUNDARY stats
- Register ANYTIME_STATS_UPDATE_TIMEOUT that fires every 1 second, calling
pgstat_report_anytime_stat(false)
The force parameter in pgstat_report_anytime_stat() is currently unused (always
called with force=false) but reserved for future use cases requiring immediate
flushing.
---
src/backend/tcop/postgres.c | 18 +++++
src/backend/utils/activity/pgstat.c | 119 ++++++++++++++++++++++++----
src/backend/utils/init/globals.c | 1 +
src/backend/utils/init/postinit.c | 15 ++++
src/include/miscadmin.h | 1 +
src/include/pgstat.h | 4 +
src/include/utils/pgstat_internal.h | 11 +++
src/include/utils/timeout.h | 1 +
src/tools/pgindent/typedefs.list | 1 +
9 files changed, 154 insertions(+), 17 deletions(-)
9.7% src/backend/tcop/
70.2% src/backend/utils/activity/
9.3% src/backend/utils/init/
6.0% src/include/utils/
4.3% src/include/
diff --git a/src/backend/tcop/postgres.c b/src/backend/tcop/postgres.c
index e54bf1e760f..6a91543f80a 100644
--- a/src/backend/tcop/postgres.c
+++ b/src/backend/tcop/postgres.c
@@ -3530,6 +3530,24 @@ ProcessInterrupts(void)
pgstat_report_stat(true);
}
+ /*
+ * Flush stats outside of transaction boundary if the timeout fired.
+ * Unlike transactional stats, these can be flushed even inside a running
+ * transaction.
+ */
+ if (AnytimeStatsUpdateTimeoutPending)
+ {
+ AnytimeStatsUpdateTimeoutPending = false;
+
+ /* Skip if completely idle */
+ if (!DoingCommandRead || IsTransactionOrTransactionBlock())
+ pgstat_report_anytime_stat(false);
+
+ /* Schedule next timeout */
+ enable_timeout_after(ANYTIME_STATS_UPDATE_TIMEOUT,
+ PGSTAT_ANYTIME_FLUSH_INTERVAL);
+ }
+
if (ProcSignalBarrierPending)
ProcessProcSignalBarrier();
diff --git a/src/backend/utils/activity/pgstat.c b/src/backend/utils/activity/pgstat.c
index 11bb71cad5a..f7942e47475 100644
--- a/src/backend/utils/activity/pgstat.c
+++ b/src/backend/utils/activity/pgstat.c
@@ -187,7 +187,8 @@ static void pgstat_init_snapshot_fixed(void);
static void pgstat_reset_after_failure(void);
-static bool pgstat_flush_pending_entries(bool nowait);
+static bool pgstat_flush_pending_entries(bool nowait, bool anytime_only);
+static bool pgstat_flush_fixed_stats(bool nowait, bool anytime_only);
static void pgstat_prep_snapshot(void);
static void pgstat_build_snapshot(void);
@@ -288,6 +289,7 @@ static const PgStat_KindInfo pgstat_kind_builtin_infos[PGSTAT_KIND_BUILTIN_SIZE]
.fixed_amount = false,
.write_to_file = true,
+ .flush_behavior = FLUSH_AT_TXN_BOUNDARY,
/* so pg_stat_database entries can be seen in all databases */
.accessed_across_databases = true,
@@ -305,6 +307,7 @@ static const PgStat_KindInfo pgstat_kind_builtin_infos[PGSTAT_KIND_BUILTIN_SIZE]
.fixed_amount = false,
.write_to_file = true,
+ .flush_behavior = FLUSH_AT_TXN_BOUNDARY,
.shared_size = sizeof(PgStatShared_Relation),
.shared_data_off = offsetof(PgStatShared_Relation, stats),
@@ -321,6 +324,7 @@ static const PgStat_KindInfo pgstat_kind_builtin_infos[PGSTAT_KIND_BUILTIN_SIZE]
.fixed_amount = false,
.write_to_file = true,
+ .flush_behavior = FLUSH_AT_TXN_BOUNDARY,
.shared_size = sizeof(PgStatShared_Function),
.shared_data_off = offsetof(PgStatShared_Function, stats),
@@ -336,6 +340,7 @@ static const PgStat_KindInfo pgstat_kind_builtin_infos[PGSTAT_KIND_BUILTIN_SIZE]
.fixed_amount = false,
.write_to_file = true,
+ .flush_behavior = FLUSH_AT_TXN_BOUNDARY,
.accessed_across_databases = true,
@@ -353,6 +358,7 @@ static const PgStat_KindInfo pgstat_kind_builtin_infos[PGSTAT_KIND_BUILTIN_SIZE]
.fixed_amount = false,
.write_to_file = true,
+ .flush_behavior = FLUSH_AT_TXN_BOUNDARY,
/* so pg_stat_subscription_stats entries can be seen in all databases */
.accessed_across_databases = true,
@@ -370,6 +376,7 @@ static const PgStat_KindInfo pgstat_kind_builtin_infos[PGSTAT_KIND_BUILTIN_SIZE]
.fixed_amount = false,
.write_to_file = false,
+ .flush_behavior = FLUSH_ANYTIME,
.accessed_across_databases = true,
@@ -388,6 +395,7 @@ static const PgStat_KindInfo pgstat_kind_builtin_infos[PGSTAT_KIND_BUILTIN_SIZE]
.fixed_amount = true,
.write_to_file = true,
+ .flush_behavior = FLUSH_ANYTIME,
.snapshot_ctl_off = offsetof(PgStat_Snapshot, archiver),
.shared_ctl_off = offsetof(PgStat_ShmemControl, archiver),
@@ -404,6 +412,7 @@ static const PgStat_KindInfo pgstat_kind_builtin_infos[PGSTAT_KIND_BUILTIN_SIZE]
.fixed_amount = true,
.write_to_file = true,
+ .flush_behavior = FLUSH_ANYTIME,
.snapshot_ctl_off = offsetof(PgStat_Snapshot, bgwriter),
.shared_ctl_off = offsetof(PgStat_ShmemControl, bgwriter),
@@ -420,6 +429,7 @@ static const PgStat_KindInfo pgstat_kind_builtin_infos[PGSTAT_KIND_BUILTIN_SIZE]
.fixed_amount = true,
.write_to_file = true,
+ .flush_behavior = FLUSH_ANYTIME,
.snapshot_ctl_off = offsetof(PgStat_Snapshot, checkpointer),
.shared_ctl_off = offsetof(PgStat_ShmemControl, checkpointer),
@@ -436,6 +446,7 @@ static const PgStat_KindInfo pgstat_kind_builtin_infos[PGSTAT_KIND_BUILTIN_SIZE]
.fixed_amount = true,
.write_to_file = true,
+ .flush_behavior = FLUSH_ANYTIME,
.snapshot_ctl_off = offsetof(PgStat_Snapshot, io),
.shared_ctl_off = offsetof(PgStat_ShmemControl, io),
@@ -453,6 +464,7 @@ static const PgStat_KindInfo pgstat_kind_builtin_infos[PGSTAT_KIND_BUILTIN_SIZE]
.fixed_amount = true,
.write_to_file = true,
+ .flush_behavior = FLUSH_ANYTIME,
.snapshot_ctl_off = offsetof(PgStat_Snapshot, slru),
.shared_ctl_off = offsetof(PgStat_ShmemControl, slru),
@@ -470,6 +482,7 @@ static const PgStat_KindInfo pgstat_kind_builtin_infos[PGSTAT_KIND_BUILTIN_SIZE]
.fixed_amount = true,
.write_to_file = true,
+ .flush_behavior = FLUSH_ANYTIME,
.snapshot_ctl_off = offsetof(PgStat_Snapshot, wal),
.shared_ctl_off = offsetof(PgStat_ShmemControl, wal),
@@ -775,23 +788,11 @@ pgstat_report_stat(bool force)
partial_flush = false;
/* flush of variable-numbered stats tracked in pending entries list */
- partial_flush |= pgstat_flush_pending_entries(nowait);
+ partial_flush |= pgstat_flush_pending_entries(nowait, false);
/* flush of other stats kinds */
if (pgstat_report_fixed)
- {
- for (PgStat_Kind kind = PGSTAT_KIND_MIN; kind <= PGSTAT_KIND_MAX; kind++)
- {
- const PgStat_KindInfo *kind_info = pgstat_get_kind_info(kind);
-
- if (!kind_info)
- continue;
- if (!kind_info->flush_static_cb)
- continue;
-
- partial_flush |= kind_info->flush_static_cb(nowait);
- }
- }
+ partial_flush |= pgstat_flush_fixed_stats(nowait, false);
last_flush = now;
@@ -1345,9 +1346,14 @@ pgstat_delete_pending_entry(PgStat_EntryRef *entry_ref)
/*
* Flush out pending variable-numbered stats.
+ *
+ * If anytime_only is true, only flushes FLUSH_ANYTIME entries.
+ * This is safe to call inside transactions.
+ *
+ * If anytime_only is false, flushes all entries.
*/
static bool
-pgstat_flush_pending_entries(bool nowait)
+pgstat_flush_pending_entries(bool nowait, bool anytime_only)
{
bool have_pending = false;
dlist_node *cur = NULL;
@@ -1377,6 +1383,20 @@ pgstat_flush_pending_entries(bool nowait)
Assert(!kind_info->fixed_amount);
Assert(kind_info->flush_pending_cb != NULL);
+ /* Skip transactional stats if we're in anytime_only mode */
+ if (anytime_only && kind_info->flush_behavior == FLUSH_AT_TXN_BOUNDARY)
+ {
+ have_pending = true;
+
+ if (dlist_has_next(&pgStatPending, cur))
+ next = dlist_next_node(&pgStatPending, cur);
+ else
+ next = NULL;
+
+ cur = next;
+ continue;
+ }
+
/* flush the stats, if possible */
did_flush = kind_info->flush_pending_cb(entry_ref, nowait);
@@ -1397,11 +1417,42 @@ pgstat_flush_pending_entries(bool nowait)
cur = next;
}
- Assert(dlist_is_empty(&pgStatPending) == !have_pending);
+ /*
+ * When in anytime_only mode, the list may not be empty because
+ * FLUSH_AT_TXN_BOUNDARY entries were skipped.
+ */
+ Assert(!anytime_only || dlist_is_empty(&pgStatPending) == !have_pending);
return have_pending;
}
+/*
+ * Flush fixed-amount stats.
+ *
+ * If anytime_only is true, only flushes FLUSH_ANYTIME stats (safe inside transactions).
+ * If anytime_only is false, flushes all stats with flush_static_cb.
+ */
+static bool
+pgstat_flush_fixed_stats(bool nowait, bool anytime_only)
+{
+ bool partial_flush = false;
+
+ for (PgStat_Kind kind = PGSTAT_KIND_MIN; kind <= PGSTAT_KIND_MAX; kind++)
+ {
+ const PgStat_KindInfo *kind_info = pgstat_get_kind_info(kind);
+
+ if (!kind_info || !kind_info->flush_static_cb)
+ continue;
+
+ /* Skip transactional stats if we're in anytime_only mode */
+ if (anytime_only && kind_info->flush_behavior == FLUSH_AT_TXN_BOUNDARY)
+ continue;
+
+ partial_flush |= kind_info->flush_static_cb(nowait);
+ }
+
+ return partial_flush;
+}
/* ------------------------------------------------------------
* Helper / infrastructure functions
@@ -2119,3 +2170,37 @@ assign_stats_fetch_consistency(int newval, void *extra)
if (pgstat_fetch_consistency != newval)
force_stats_snapshot_clear = true;
}
+
+/*
+ * Flush non-transactional stats
+ *
+ * This is safe to call even inside a transaction. It only flushes stats
+ * kinds marked as FLUSH_ANYTIME.
+ *
+ * This allows long running transactions to report activity without waiting
+ * for transaction to finish.
+ */
+void
+pgstat_report_anytime_stat(bool force)
+{
+ bool nowait = !force;
+
+ pgstat_assert_is_up();
+
+ /*
+ * Exit if no pending stats at all. This avoids unnecessary work when
+ * backends are idle or in sessions without stats accumulation.
+ *
+ * Note: This check isn't precise as there might be only transactional
+ * stats pending, which we'll skip during the flush. However, maintaining
+ * precise tracking would add complexity that does not seem worth it from
+ * a performance point of view (no noticeable performance regression has
+ * been observed with the current implementation).
+ */
+ if (dlist_is_empty(&pgStatPending) && !pgstat_report_fixed)
+ return;
+
+ /* Flush stats outside of transaction boundary */
+ pgstat_flush_pending_entries(nowait, true);
+ pgstat_flush_fixed_stats(nowait, true);
+}
diff --git a/src/backend/utils/init/globals.c b/src/backend/utils/init/globals.c
index 36ad708b360..ad44826c39e 100644
--- a/src/backend/utils/init/globals.c
+++ b/src/backend/utils/init/globals.c
@@ -40,6 +40,7 @@ volatile sig_atomic_t IdleSessionTimeoutPending = false;
volatile sig_atomic_t ProcSignalBarrierPending = false;
volatile sig_atomic_t LogMemoryContextPending = false;
volatile sig_atomic_t IdleStatsUpdateTimeoutPending = false;
+volatile sig_atomic_t AnytimeStatsUpdateTimeoutPending = false;
volatile uint32 InterruptHoldoffCount = 0;
volatile uint32 QueryCancelHoldoffCount = 0;
volatile uint32 CritSectionCount = 0;
diff --git a/src/backend/utils/init/postinit.c b/src/backend/utils/init/postinit.c
index 3f401faf3de..cb0f6aecad1 100644
--- a/src/backend/utils/init/postinit.c
+++ b/src/backend/utils/init/postinit.c
@@ -82,6 +82,7 @@ static void TransactionTimeoutHandler(void);
static void IdleSessionTimeoutHandler(void);
static void IdleStatsUpdateTimeoutHandler(void);
static void ClientCheckTimeoutHandler(void);
+static void AnytimeStatsUpdateTimeoutHandler(void);
static bool ThereIsAtLeastOneRole(void);
static void process_startup_options(Port *port, bool am_superuser);
static void process_settings(Oid databaseid, Oid roleid);
@@ -765,6 +766,9 @@ InitPostgres(const char *in_dbname, Oid dboid,
RegisterTimeout(CLIENT_CONNECTION_CHECK_TIMEOUT, ClientCheckTimeoutHandler);
RegisterTimeout(IDLE_STATS_UPDATE_TIMEOUT,
IdleStatsUpdateTimeoutHandler);
+ RegisterTimeout(ANYTIME_STATS_UPDATE_TIMEOUT,
+ AnytimeStatsUpdateTimeoutHandler);
+ enable_timeout_after(ANYTIME_STATS_UPDATE_TIMEOUT, PGSTAT_ANYTIME_FLUSH_INTERVAL);
}
/*
@@ -1446,3 +1450,14 @@ ThereIsAtLeastOneRole(void)
return result;
}
+
+/*
+ * Timeout handler for flushing non-transactional stats.
+ */
+static void
+AnytimeStatsUpdateTimeoutHandler(void)
+{
+ AnytimeStatsUpdateTimeoutPending = true;
+ InterruptPending = true;
+ SetLatch(MyLatch);
+}
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index db559b39c4d..8aeb9628871 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -96,6 +96,7 @@ extern PGDLLIMPORT volatile sig_atomic_t IdleSessionTimeoutPending;
extern PGDLLIMPORT volatile sig_atomic_t ProcSignalBarrierPending;
extern PGDLLIMPORT volatile sig_atomic_t LogMemoryContextPending;
extern PGDLLIMPORT volatile sig_atomic_t IdleStatsUpdateTimeoutPending;
+extern PGDLLIMPORT volatile sig_atomic_t AnytimeStatsUpdateTimeoutPending;
extern PGDLLIMPORT volatile sig_atomic_t CheckClientConnectionPending;
extern PGDLLIMPORT volatile sig_atomic_t ClientConnectionLost;
diff --git a/src/include/pgstat.h b/src/include/pgstat.h
index fff7ecc2533..86e65397614 100644
--- a/src/include/pgstat.h
+++ b/src/include/pgstat.h
@@ -35,6 +35,9 @@
/* Default directory to store temporary statistics data in */
#define PG_STAT_TMP_DIR "pg_stat_tmp"
+/* When to call pgstat_report_anytime_stat() again */
+#define PGSTAT_ANYTIME_FLUSH_INTERVAL 1000
+
/* Values for track_functions GUC variable --- order is significant! */
typedef enum TrackFunctionsLevel
{
@@ -533,6 +536,7 @@ extern void pgstat_initialize(void);
/* Functions called from backends */
extern long pgstat_report_stat(bool force);
+extern void pgstat_report_anytime_stat(bool force);
extern void pgstat_force_next_flush(void);
extern void pgstat_reset_counters(void);
diff --git a/src/include/utils/pgstat_internal.h b/src/include/utils/pgstat_internal.h
index 9b8fbae00ed..02f4f13fc0f 100644
--- a/src/include/utils/pgstat_internal.h
+++ b/src/include/utils/pgstat_internal.h
@@ -224,6 +224,14 @@ typedef struct PgStat_SubXactStatus
PgStat_TableXactStatus *first; /* head of list for this subxact */
} PgStat_SubXactStatus;
+/*
+ * Flush behavior for statistics kinds.
+ */
+typedef enum PgStat_FlushBehavior
+{
+ FLUSH_ANYTIME, /* All fields can flush anytime */
+ FLUSH_AT_TXN_BOUNDARY, /* All fields need transaction boundary */
+} PgStat_FlushBehavior;
/*
* Metadata for a specific kind of statistics.
@@ -251,6 +259,9 @@ typedef struct PgStat_KindInfo
*/
bool track_entry_count:1;
+ /* Flush behavior */
+ PgStat_FlushBehavior flush_behavior;
+
/*
* The size of an entry in the shared stats hash table (pointed to by
* PgStatShared_HashEntry->body). For fixed-numbered statistics, this is
diff --git a/src/include/utils/timeout.h b/src/include/utils/timeout.h
index 0965b590b34..10723bb664c 100644
--- a/src/include/utils/timeout.h
+++ b/src/include/utils/timeout.h
@@ -35,6 +35,7 @@ typedef enum TimeoutId
IDLE_SESSION_TIMEOUT,
IDLE_STATS_UPDATE_TIMEOUT,
CLIENT_CONNECTION_CHECK_TIMEOUT,
+ ANYTIME_STATS_UPDATE_TIMEOUT,
STARTUP_PROGRESS_TIMEOUT,
/* First user-definable timeout reason */
USER_TIMEOUT,
diff --git a/src/tools/pgindent/typedefs.list b/src/tools/pgindent/typedefs.list
index 09e7f1d420e..9aabb325f16 100644
--- a/src/tools/pgindent/typedefs.list
+++ b/src/tools/pgindent/typedefs.list
@@ -2261,6 +2261,7 @@ PgStat_Counter
PgStat_EntryRef
PgStat_EntryRefHashEntry
PgStat_FetchConsistency
+PgStat_FlushBehavior
PgStat_FunctionCallUsage
PgStat_FunctionCounts
PgStat_HashKey
--
2.34.1
--tjEWjIIwfNIHQLgt
Content-Type: text/x-diff; charset=us-ascii
Content-Disposition: attachment;
filename="v1-0002-Remove-useless-calls-to-flush-some-stats.patch"
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