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Commit13eb6bb

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Fix performance regression with flush of pending fixed-numbered stats
The callback added infc415ed used to check if there is any pendingdata to flush for fixed-numbered statistics, done by looping across allthe builtin and custom stats kinds with a call to have_fixed_pending_cb,is proving to able to show in workloads that do not report any stats(read-only, no function calls, no WAL, no IO, etc). The code used inv17 was cheaper than that what HEAD has introduced, relying on threeboolean checks for WAL, SLRU and IO stats.This commit switches the code to use a more efficient approach thanfc415ed, with a single boolean flag that can be switched to "true"by any fixed-numbered stats kinds to force pgstat_report_stat() to gothrough one round of reports. The flag is reset by pgstat_report_stat()once a full round of reports is done. The flag being false means thatfixed-numbered stats kinds saw no activity, and that there is no pendingdata to flush.ac000fc took one step in improving the performance by reducing thenumber of stats kinds that the backend can hold. This commit takes amore drastic step by bringing back the code efficiency to what it wasbefore v18 with a cheap check at the beginning of pgstat_report_stat()for its fast-exit path.The callback have_static_pending_cb is removed as an effect of all that.Reported-by: Andres Freund <andres@anarazel.de>Reviewed-by: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>Discussion:https://postgr.es/m/eb224uegsga2hgq7dfq3ps5cduhpqej7ir2hjxzzozjthrekx5@dysei6buqtheBackpatch-through: 18
1 parentbae5078 commit13eb6bb

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7 files changed

+62
-88
lines changed

7 files changed

+62
-88
lines changed

‎src/backend/access/transam/xlog.c‎

Lines changed: 10 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -96,6 +96,7 @@
9696
#include"utils/guc_hooks.h"
9797
#include"utils/guc_tables.h"
9898
#include"utils/injection_point.h"
99+
#include"utils/pgstat_internal.h"
99100
#include"utils/ps_status.h"
100101
#include"utils/relmapper.h"
101102
#include"utils/snapmgr.h"
@@ -1092,6 +1093,9 @@ XLogInsertRecord(XLogRecData *rdata,
10921093
pgWalUsage.wal_bytes+=rechdr->xl_tot_len;
10931094
pgWalUsage.wal_records++;
10941095
pgWalUsage.wal_fpi+=num_fpi;
1096+
1097+
/* Required for the flush of pending stats WAL data */
1098+
pgstat_report_fixed= true;
10951099
}
10961100

10971101
returnEndPos;
@@ -2109,6 +2113,12 @@ AdvanceXLInsertBuffer(XLogRecPtr upto, TimeLineID tli, bool opportunistic)
21092113
LWLockRelease(WALWriteLock);
21102114
pgWalUsage.wal_buffers_full++;
21112115
TRACE_POSTGRESQL_WAL_BUFFER_WRITE_DIRTY_DONE();
2116+
2117+
/*
2118+
* Required for the flush of pending stats WAL data, per
2119+
* update of pgWalUsage.
2120+
*/
2121+
pgstat_report_fixed= true;
21122122
}
21132123
}
21142124
}

‎src/backend/utils/activity/pgstat.c‎

Lines changed: 19 additions & 33 deletions
Original file line numberDiff line numberDiff line change
@@ -212,6 +212,11 @@ intpgstat_fetch_consistency = PGSTAT_FETCH_CONSISTENCY_CACHE;
212212

213213
PgStat_LocalStatepgStatLocal;
214214

215+
/*
216+
* Track pending reports for fixed-numbered stats, used by
217+
* pgstat_report_stat().
218+
*/
219+
boolpgstat_report_fixed= false;
215220

216221
/* ----------
217222
* Local data
@@ -370,7 +375,6 @@ static const PgStat_KindInfo pgstat_kind_builtin_infos[PGSTAT_KIND_BUILTIN_SIZE]
370375
.shared_data_off= offsetof(PgStatShared_Backend,stats),
371376
.shared_data_len=sizeof(((PgStatShared_Backend*)0)->stats),
372377

373-
.have_static_pending_cb=pgstat_backend_have_pending_cb,
374378
.flush_static_cb=pgstat_backend_flush_cb,
375379
.reset_timestamp_cb=pgstat_backend_reset_timestamp_cb,
376380
},
@@ -437,7 +441,6 @@ static const PgStat_KindInfo pgstat_kind_builtin_infos[PGSTAT_KIND_BUILTIN_SIZE]
437441
.shared_data_len=sizeof(((PgStatShared_IO*)0)->stats),
438442

439443
.flush_static_cb=pgstat_io_flush_cb,
440-
.have_static_pending_cb=pgstat_io_have_pending_cb,
441444
.init_shmem_cb=pgstat_io_init_shmem_cb,
442445
.reset_all_cb=pgstat_io_reset_all_cb,
443446
.snapshot_cb=pgstat_io_snapshot_cb,
@@ -455,7 +458,6 @@ static const PgStat_KindInfo pgstat_kind_builtin_infos[PGSTAT_KIND_BUILTIN_SIZE]
455458
.shared_data_len=sizeof(((PgStatShared_SLRU*)0)->stats),
456459

457460
.flush_static_cb=pgstat_slru_flush_cb,
458-
.have_static_pending_cb=pgstat_slru_have_pending_cb,
459461
.init_shmem_cb=pgstat_slru_init_shmem_cb,
460462
.reset_all_cb=pgstat_slru_reset_all_cb,
461463
.snapshot_cb=pgstat_slru_snapshot_cb,
@@ -474,7 +476,6 @@ static const PgStat_KindInfo pgstat_kind_builtin_infos[PGSTAT_KIND_BUILTIN_SIZE]
474476

475477
.init_backend_cb=pgstat_wal_init_backend_cb,
476478
.flush_static_cb=pgstat_wal_flush_cb,
477-
.have_static_pending_cb=pgstat_wal_have_pending_cb,
478479
.init_shmem_cb=pgstat_wal_init_shmem_cb,
479480
.reset_all_cb=pgstat_wal_reset_all_cb,
480481
.snapshot_cb=pgstat_wal_snapshot_cb,
@@ -708,29 +709,10 @@ pgstat_report_stat(bool force)
708709
}
709710

710711
/* Don't expend a clock check if nothing to do */
711-
if (dlist_is_empty(&pgStatPending))
712+
if (dlist_is_empty(&pgStatPending)&&
713+
!pgstat_report_fixed)
712714
{
713-
booldo_flush= false;
714-
715-
/* Check for pending stats */
716-
for (PgStat_Kindkind=PGSTAT_KIND_MIN;kind <=PGSTAT_KIND_MAX;kind++)
717-
{
718-
constPgStat_KindInfo*kind_info=pgstat_get_kind_info(kind);
719-
720-
if (!kind_info)
721-
continue;
722-
if (!kind_info->have_static_pending_cb)
723-
continue;
724-
725-
if (kind_info->have_static_pending_cb())
726-
{
727-
do_flush= true;
728-
break;
729-
}
730-
}
731-
732-
if (!do_flush)
733-
return0;
715+
return0;
734716
}
735717

736718
/*
@@ -784,16 +766,19 @@ pgstat_report_stat(bool force)
784766
partial_flush |=pgstat_flush_pending_entries(nowait);
785767

786768
/* flush of other stats kinds */
787-
for (PgStat_Kindkind=PGSTAT_KIND_MIN;kind <=PGSTAT_KIND_MAX;kind++)
769+
if (pgstat_report_fixed)
788770
{
789-
constPgStat_KindInfo*kind_info=pgstat_get_kind_info(kind);
771+
for (PgStat_Kindkind=PGSTAT_KIND_MIN;kind <=PGSTAT_KIND_MAX;kind++)
772+
{
773+
constPgStat_KindInfo*kind_info=pgstat_get_kind_info(kind);
790774

791-
if (!kind_info)
792-
continue;
793-
if (!kind_info->flush_static_cb)
794-
continue;
775+
if (!kind_info)
776+
continue;
777+
if (!kind_info->flush_static_cb)
778+
continue;
795779

796-
partial_flush |=kind_info->flush_static_cb(nowait);
780+
partial_flush |=kind_info->flush_static_cb(nowait);
781+
}
797782
}
798783

799784
last_flush=now;
@@ -815,6 +800,7 @@ pgstat_report_stat(bool force)
815800
}
816801

817802
pending_since=0;
803+
pgstat_report_fixed= false;
818804

819805
return0;
820806
}

‎src/backend/utils/activity/pgstat_backend.c‎

Lines changed: 2 additions & 12 deletions
Original file line numberDiff line numberDiff line change
@@ -66,6 +66,7 @@ pgstat_count_backend_io_op_time(IOObject io_object, IOContext io_context,
6666
io_time);
6767

6868
backend_has_iostats= true;
69+
pgstat_report_fixed= true;
6970
}
7071

7172
void
@@ -81,6 +82,7 @@ pgstat_count_backend_io_op(IOObject io_object, IOContext io_context,
8182
PendingBackendStats.pending_io.bytes[io_object][io_context][io_op]+=bytes;
8283

8384
backend_has_iostats= true;
85+
pgstat_report_fixed= true;
8486
}
8587

8688
/*
@@ -301,18 +303,6 @@ pgstat_flush_backend(bool nowait, bits32 flags)
301303
return false;
302304
}
303305

304-
/*
305-
* Check if there are any backend stats waiting for flush.
306-
*/
307-
bool
308-
pgstat_backend_have_pending_cb(void)
309-
{
310-
if (!pgstat_tracks_backend_bktype(MyBackendType))
311-
return false;
312-
313-
return (backend_has_iostats||pgstat_backend_wal_have_pending());
314-
}
315-
316306
/*
317307
* Callback to flush out locally pending backend statistics.
318308
*

‎src/backend/utils/activity/pgstat_io.c‎

Lines changed: 1 addition & 9 deletions
Original file line numberDiff line numberDiff line change
@@ -80,6 +80,7 @@ pgstat_count_io_op(IOObject io_object, IOContext io_context, IOOp io_op,
8080
pgstat_count_backend_io_op(io_object,io_context,io_op,cnt,bytes);
8181

8282
have_iostats= true;
83+
pgstat_report_fixed= true;
8384
}
8485

8586
/*
@@ -167,15 +168,6 @@ pgstat_fetch_stat_io(void)
167168
return&pgStatLocal.snapshot.io;
168169
}
169170

170-
/*
171-
* Check if there any IO stats waiting for flush.
172-
*/
173-
bool
174-
pgstat_io_have_pending_cb(void)
175-
{
176-
returnhave_iostats;
177-
}
178-
179171
/*
180172
* Simpler wrapper of pgstat_io_flush_cb()
181173
*/

‎src/backend/utils/activity/pgstat_slru.c‎

Lines changed: 1 addition & 9 deletions
Original file line numberDiff line numberDiff line change
@@ -143,15 +143,6 @@ pgstat_get_slru_index(const char *name)
143143
return (SLRU_NUM_ELEMENTS-1);
144144
}
145145

146-
/*
147-
* Check if there are any SLRU stats entries waiting for flush.
148-
*/
149-
bool
150-
pgstat_slru_have_pending_cb(void)
151-
{
152-
returnhave_slrustats;
153-
}
154-
155146
/*
156147
* Flush out locally pending SLRU stats entries
157148
*
@@ -247,6 +238,7 @@ get_slru_entry(int slru_idx)
247238
Assert((slru_idx >=0)&& (slru_idx<SLRU_NUM_ELEMENTS));
248239

249240
have_slrustats= true;
241+
pgstat_report_fixed= true;
250242

251243
return&pending_SLRUStats[slru_idx];
252244
}

‎src/backend/utils/activity/pgstat_wal.c‎

Lines changed: 10 additions & 10 deletions
Original file line numberDiff line numberDiff line change
@@ -71,6 +71,15 @@ pgstat_fetch_stat_wal(void)
7171
return&pgStatLocal.snapshot.wal;
7272
}
7373

74+
/*
75+
* To determine whether WAL usage happened.
76+
*/
77+
staticinlinebool
78+
pgstat_wal_have_pending(void)
79+
{
80+
returnpgWalUsage.wal_records!=prevWalUsage.wal_records;
81+
}
82+
7483
/*
7584
* Calculate how much WAL usage counters have increased by subtracting the
7685
* previous counters from the current ones.
@@ -92,7 +101,7 @@ pgstat_wal_flush_cb(bool nowait)
92101
* This function can be called even if nothing at all has happened. Avoid
93102
* taking lock for nothing in that case.
94103
*/
95-
if (!pgstat_wal_have_pending_cb())
104+
if (!pgstat_wal_have_pending())
96105
return false;
97106

98107
/*
@@ -136,15 +145,6 @@ pgstat_wal_init_backend_cb(void)
136145
prevWalUsage=pgWalUsage;
137146
}
138147

139-
/*
140-
* To determine whether WAL usage happened.
141-
*/
142-
bool
143-
pgstat_wal_have_pending_cb(void)
144-
{
145-
returnpgWalUsage.wal_records!=prevWalUsage.wal_records;
146-
}
147-
148148
void
149149
pgstat_wal_init_shmem_cb(void*stats)
150150
{

‎src/include/utils/pgstat_internal.h‎

Lines changed: 19 additions & 15 deletions
Original file line numberDiff line numberDiff line change
@@ -295,18 +295,11 @@ typedef struct PgStat_KindInfo
295295
*
296296
* Returns true if some of the stats could not be flushed, due to lock
297297
* contention for example. Optional.
298-
*/
299-
bool(*flush_static_cb) (boolnowait);
300-
301-
/*
302-
* For fixed-numbered or variable-numbered statistics: Check for pending
303-
* stats in need of flush with flush_static_cb, when these do not use
304-
* PgStat_EntryRef->pending.
305298
*
306-
*Returns true if there are any stats pending forflush, triggering
307-
*flush_static_cb. Optional.
299+
*"pgstat_report_fixed" needs to be set to trigger theflush of pending
300+
*stats.
308301
*/
309-
bool(*have_static_pending_cb) (void);
302+
bool(*flush_static_cb) (boolnowait);
310303

311304
/*
312305
* For fixed-numbered statistics: Reset All.
@@ -627,7 +620,6 @@ extern void pgstat_archiver_snapshot_cb(void);
627620

628621
externboolpgstat_flush_backend(boolnowait,bits32flags);
629622
externboolpgstat_backend_flush_cb(boolnowait);
630-
externboolpgstat_backend_have_pending_cb(void);
631623
externvoidpgstat_backend_reset_timestamp_cb(PgStatShared_Common*header,
632624
TimestampTzts);
633625

@@ -676,7 +668,6 @@ extern bool pgstat_function_flush_cb(PgStat_EntryRef *entry_ref, bool nowait);
676668

677669
externvoidpgstat_flush_io(boolnowait);
678670

679-
externboolpgstat_io_have_pending_cb(void);
680671
externboolpgstat_io_flush_cb(boolnowait);
681672
externvoidpgstat_io_init_shmem_cb(void*stats);
682673
externvoidpgstat_io_reset_all_cb(TimestampTzts);
@@ -738,7 +729,6 @@ extern PgStatShared_Common *pgstat_init_entry(PgStat_Kind kind,
738729
* Functions in pgstat_slru.c
739730
*/
740731

741-
externboolpgstat_slru_have_pending_cb(void);
742732
externboolpgstat_slru_flush_cb(boolnowait);
743733
externvoidpgstat_slru_init_shmem_cb(void*stats);
744734
externvoidpgstat_slru_reset_all_cb(TimestampTzts);
@@ -750,7 +740,6 @@ extern void pgstat_slru_snapshot_cb(void);
750740
*/
751741

752742
externvoidpgstat_wal_init_backend_cb(void);
753-
externboolpgstat_wal_have_pending_cb(void);
754743
externboolpgstat_wal_flush_cb(boolnowait);
755744
externvoidpgstat_wal_init_shmem_cb(void*stats);
756745
externvoidpgstat_wal_reset_all_cb(TimestampTzts);
@@ -778,8 +767,23 @@ extern void pgstat_create_transactional(PgStat_Kind kind, Oid dboid, uint64 obji
778767
* Variables in pgstat.c
779768
*/
780769

781-
externPGDLLIMPORTPgStat_LocalStatepgStatLocal;
770+
/*
771+
* Track if *any* pending fixed-numbered statistics should be flushed to
772+
* shared memory.
773+
*
774+
* This flag can be switched to true by fixed-numbered statistics to let
775+
* pgstat_report_stat() know if it needs to go through one round of
776+
* reports, calling flush_static_cb for each fixed-numbered statistics
777+
* kind. When this flag is not set, pgstat_report_stat() is able to do
778+
* a fast exit, knowing that there are no pending fixed-numbered statistics.
779+
*
780+
* Statistics callbacks should never reset this flag; pgstat_report_stat()
781+
* is in charge of doing that.
782+
*/
783+
externPGDLLIMPORTboolpgstat_report_fixed;
782784

785+
/* Backend-local stats state */
786+
externPGDLLIMPORTPgStat_LocalStatepgStatLocal;
783787

784788
/*
785789
* Implementation of inline functions declared above.

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