This commit adds per-backend WAL statistics, providing the same
information as pg_stat_wal, except that it is now possible to know how
much WAL activity is happening in each backend rather than an overall
aggregate of all the activity. Like pg_stat_wal, the implementation
relies on pgWalUsage, tracking the difference of activity between two
reports to pgstats.
This data can be retrieved with a new system function called
pg_stat_get_backend_wal(), that returns one tuple based on the PID
provided in input. Like pg_stat_get_backend_io(), this is useful when
joined with pg_stat_activity to get a live picture of the WAL generated
for each running backend, showing how the activity is [un]balanced.
pgstat_flush_backend() gains a new flag value, able to control the flush
of the WAL stats.
This commit relies mostly on the infrastructure provided by
9aea73fc61d4, that has introduced backend statistics.
Bump catalog version. A bump of PGSTAT_FILE_FORMAT_ID is not required,
as backend stats do not persist on disk.
Author: Bertrand Drouvot <
[email protected]>
Reviewed-by: Michael Paquier <[email protected]>
Reviewed-by: Nazir Bilal Yavuz <[email protected]>
Reviewed-by: Xuneng Zhou <[email protected]>
Discussion: https://postgr.es/m/Z3zqc4o09dM/
[email protected]
</para></entry>
</row>
+ <row>
+ <entry id="pg-stat-get-backend-wal" role="func_table_entry"><para role="func_signature">
+ <indexterm>
+ <primary>pg_stat_get_backend_wal</primary>
+ </indexterm>
+ <function>pg_stat_get_backend_wal</function> ( <type>integer</type> )
+ <returnvalue>record</returnvalue>
+ </para>
+ <para>
+ Returns WAL statistics about the backend with the specified
+ process ID. The output fields are exactly the same as the ones in the
+ <structname>pg_stat_wal</structname> view.
+ </para>
+ <para>
+ The function does not return WAL statistics for the checkpointer,
+ the background writer, the startup process and the autovacuum launcher.
+ </para></entry>
+ </row>
+
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
*/
static PgStat_BackendPending PendingBackendStats = {0};
+/*
+ * WAL usage counters saved from pgWalUsage at the previous call to
+ * pgstat_report_wal(). This is used to calculate how much WAL usage
+ * happens between pgstat_report_wal() calls, by subtracting the previous
+ * counters from the current ones.
+ */
+static WalUsage prevBackendWalUsage;
+
/*
* Utility routines to report I/O stats for backends, kept here to avoid
* exposing PendingBackendStats to the outside world.
MemSet(&PendingBackendStats.pending_io, 0, sizeof(PgStat_PendingIO));
}
+/*
+ * To determine whether WAL usage happened.
+ */
+static inline bool
+pgstat_backend_wal_have_pending(void)
+{
+ return (pgWalUsage.wal_records != prevBackendWalUsage.wal_records);
+}
+
+/*
+ * Flush out locally pending backend WAL statistics. Locking is managed
+ * by the caller.
+ */
+static void
+pgstat_flush_backend_entry_wal(PgStat_EntryRef *entry_ref)
+{
+ PgStatShared_Backend *shbackendent;
+ PgStat_WalCounters *bktype_shstats;
+ WalUsage wal_usage_diff = {0};
+
+ /*
+ * This function can be called even if nothing at all has happened for WAL
+ * statistics. In this case, avoid unnecessarily modifying the stats
+ * entry.
+ */
+ if (!pgstat_backend_wal_have_pending())
+ return;
+
+ shbackendent = (PgStatShared_Backend *) entry_ref->shared_stats;
+ bktype_shstats = &shbackendent->stats.wal_counters;
+
+ /*
+ * Calculate how much WAL usage counters were increased by subtracting the
+ * previous counters from the current ones.
+ */
+ WalUsageAccumDiff(&wal_usage_diff, &pgWalUsage, &prevBackendWalUsage);
+
+#define WALSTAT_ACC(fld, var_to_add) \
+ (bktype_shstats->fld += var_to_add.fld)
+ WALSTAT_ACC(wal_buffers_full, wal_usage_diff);
+ WALSTAT_ACC(wal_records, wal_usage_diff);
+ WALSTAT_ACC(wal_fpi, wal_usage_diff);
+ WALSTAT_ACC(wal_bytes, wal_usage_diff);
+#undef WALSTAT_ACC
+
+ /*
+ * Save the current counters for the subsequent calculation of WAL usage.
+ */
+ prevBackendWalUsage = pgWalUsage;
+}
+
/*
* Flush out locally pending backend statistics
*
pgstat_flush_backend(bool nowait, bits32 flags)
{
PgStat_EntryRef *entry_ref;
+ bool has_pending_data = false;
if (!pgstat_tracks_backend_bktype(MyBackendType))
return false;
- if (pg_memory_is_all_zeros(&PendingBackendStats,
- sizeof(struct PgStat_BackendPending)))
+ /* Some IO data pending? */
+ if ((flags & PGSTAT_BACKEND_FLUSH_IO) &&
+ !pg_memory_is_all_zeros(&PendingBackendStats.pending_io,
+ sizeof(struct PgStat_PendingIO)))
+ has_pending_data = true;
+
+ /* Some WAL data pending? */
+ if ((flags & PGSTAT_BACKEND_FLUSH_WAL) &&
+ pgstat_backend_wal_have_pending())
+ has_pending_data = true;
+
+ if (!has_pending_data)
return false;
entry_ref = pgstat_get_entry_ref_locked(PGSTAT_KIND_BACKEND, InvalidOid,
if (flags & PGSTAT_BACKEND_FLUSH_IO)
pgstat_flush_backend_entry_io(entry_ref);
+ if (flags & PGSTAT_BACKEND_FLUSH_WAL)
+ pgstat_flush_backend_entry_wal(entry_ref);
+
pgstat_unlock_entry(entry_ref);
return false;
return false;
return (!pg_memory_is_all_zeros(&PendingBackendStats,
- sizeof(struct PgStat_BackendPending)));
+ sizeof(struct PgStat_BackendPending)) ||
+ pgstat_backend_wal_have_pending());
}
/*
pgstat_unlock_entry(entry_ref);
MemSet(&PendingBackendStats, 0, sizeof(PgStat_BackendPending));
+
+ /*
+ * Initialize prevBackendWalUsage with pgWalUsage so that
+ * pgstat_backend_flush_cb() can calculate how much pgWalUsage counters
+ * are increased by subtracting prevBackendWalUsage from pgWalUsage.
+ */
+ prevBackendWalUsage = pgWalUsage;
}
/*
/* flush wal stats */
(void) pgstat_wal_flush_cb(nowait);
+ pgstat_flush_backend(nowait, PGSTAT_BACKEND_FLUSH_WAL);
/* flush IO stats */
pgstat_flush_io(nowait);
/*
* pg_stat_wal_build_tuple
*
- * Helper routine for pg_stat_get_wal() returning one tuple based on the
- * contents of wal_counters.
+ * Helper routine for pg_stat_get_wal() and pg_stat_get_backend_wal()
+ * returning one tuple based on the contents of wal_counters.
*/
static Datum
pg_stat_wal_build_tuple(PgStat_WalCounters wal_counters,
PG_RETURN_DATUM(HeapTupleGetDatum(heap_form_tuple(tupdesc, values, nulls)));
}
+/*
+ * Returns WAL statistics for a backend with given PID.
+ */
+Datum
+pg_stat_get_backend_wal(PG_FUNCTION_ARGS)
+{
+ int pid;
+ PgStat_Backend *backend_stats;
+ PgStat_WalCounters bktype_stats;
+
+ pid = PG_GETARG_INT32(0);
+ backend_stats = pgstat_fetch_stat_backend_by_pid(pid, NULL);
+
+ if (!backend_stats)
+ PG_RETURN_NULL();
+
+ bktype_stats = backend_stats->wal_counters;
+
+ /* save tuples with data from this PgStat_WalCounters */
+ return (pg_stat_wal_build_tuple(bktype_stats, backend_stats->stat_reset_timestamp));
+}
+
/*
* Returns statistics of WAL activity
*/
*/
/* yyyymmddN */
-#define CATALOG_VERSION_NO 202503071
+#define CATALOG_VERSION_NO 202503111
#endif
proargmodes => '{o,o,o,o,o}',
proargnames => '{wal_records,wal_fpi,wal_bytes,wal_buffers_full,stats_reset}',
prosrc => 'pg_stat_get_wal' },
+{ oid => '8037', descr => 'statistics: backend WAL activity',
+ proname => 'pg_stat_get_backend_wal', provolatile => 'v', proparallel => 'r',
+ prorettype => 'record', proargtypes => 'int4',
+ proallargtypes => '{int4,int8,int8,numeric,int8,timestamptz}',
+ proargmodes => '{i,o,o,o,o,o}',
+ proargnames => '{backend_pid,wal_records,wal_fpi,wal_bytes,wal_buffers_full,stats_reset}',
+ prosrc => 'pg_stat_get_backend_wal' },
{ oid => '6248', descr => 'statistics: information about WAL prefetching',
proname => 'pg_stat_get_recovery_prefetch', prorows => '1', proretset => 't',
provolatile => 'v', prorettype => 'record', proargtypes => '',
PgStat_BktypeIO stats[BACKEND_NUM_TYPES];
} PgStat_IO;
-typedef struct PgStat_Backend
-{
- TimestampTz stat_reset_timestamp;
- PgStat_BktypeIO io_stats;
-} PgStat_Backend;
-
-/* ---------
- * PgStat_BackendPending Non-flushed backend stats.
- * ---------
- */
-typedef struct PgStat_BackendPending
-{
- /*
- * Backend statistics store the same amount of IO data as PGSTAT_KIND_IO.
- */
- PgStat_PendingIO pending_io;
-} PgStat_BackendPending;
-
typedef struct PgStat_StatDBEntry
{
PgStat_Counter xact_commit;
TimestampTz stat_reset_timestamp;
} PgStat_WalStats;
+/* -------
+ * PgStat_Backend Backend statistics
+ * -------
+ */
+typedef struct PgStat_Backend
+{
+ TimestampTz stat_reset_timestamp;
+ PgStat_BktypeIO io_stats;
+ PgStat_WalCounters wal_counters;
+} PgStat_Backend;
+
+/* ---------
+ * PgStat_BackendPending Non-flushed backend stats.
+ * ---------
+ */
+typedef struct PgStat_BackendPending
+{
+ /*
+ * Backend statistics store the same amount of IO data as PGSTAT_KIND_IO.
+ */
+ PgStat_PendingIO pending_io;
+} PgStat_BackendPending;
+
/*
* Functions in pgstat.c
*/
/* flags for pgstat_flush_backend() */
#define PGSTAT_BACKEND_FLUSH_IO (1 << 0) /* Flush I/O statistics */
-#define PGSTAT_BACKEND_FLUSH_ALL (PGSTAT_BACKEND_FLUSH_IO)
+#define PGSTAT_BACKEND_FLUSH_WAL (1 << 1) /* Flush WAL statistics */
+#define PGSTAT_BACKEND_FLUSH_ALL (PGSTAT_BACKEND_FLUSH_IO | PGSTAT_BACKEND_FLUSH_WAL)
extern bool pgstat_flush_backend(bool nowait, bits32 flags);
extern bool pgstat_backend_flush_cb(bool nowait);
-- Test pg_stat_checkpointer checkpointer-related stats, together with pg_stat_wal
SELECT num_requested AS rqst_ckpts_before FROM pg_stat_checkpointer \gset
--- Test pg_stat_wal (and make a temp table so our temp schema exists)
+-- Test pg_stat_wal
SELECT wal_bytes AS wal_bytes_before FROM pg_stat_wal \gset
+-- Test pg_stat_get_backend_wal()
+SELECT wal_bytes AS backend_wal_bytes_before from pg_stat_get_backend_wal(pg_backend_pid()) \gset
+-- Make a temp table so our temp schema exists
CREATE TEMP TABLE test_stats_temp AS SELECT 17;
DROP TABLE test_stats_temp;
-- Checkpoint twice: The checkpointer reports stats after reporting completion
t
(1 row)
+SELECT pg_stat_force_next_flush();
+ pg_stat_force_next_flush
+--------------------------
+
+(1 row)
+
+SELECT wal_bytes > :backend_wal_bytes_before FROM pg_stat_get_backend_wal(pg_backend_pid());
+ ?column?
+----------
+ t
+(1 row)
+
-- Test pg_stat_get_backend_idset() and some allied functions.
-- In particular, verify that their notion of backend ID matches
-- our temp schema index.
-- Test pg_stat_checkpointer checkpointer-related stats, together with pg_stat_wal
SELECT num_requested AS rqst_ckpts_before FROM pg_stat_checkpointer \gset
--- Test pg_stat_wal (and make a temp table so our temp schema exists)
+-- Test pg_stat_wal
SELECT wal_bytes AS wal_bytes_before FROM pg_stat_wal \gset
+-- Test pg_stat_get_backend_wal()
+SELECT wal_bytes AS backend_wal_bytes_before from pg_stat_get_backend_wal(pg_backend_pid()) \gset
+
+-- Make a temp table so our temp schema exists
CREATE TEMP TABLE test_stats_temp AS SELECT 17;
DROP TABLE test_stats_temp;
SELECT num_requested > :rqst_ckpts_before FROM pg_stat_checkpointer;
SELECT wal_bytes > :wal_bytes_before FROM pg_stat_wal;
+SELECT pg_stat_force_next_flush();
+SELECT wal_bytes > :backend_wal_bytes_before FROM pg_stat_get_backend_wal(pg_backend_pid());
+
-- Test pg_stat_get_backend_idset() and some allied functions.
-- In particular, verify that their notion of backend ID matches
-- our temp schema index.
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