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Commitc6c9474

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Use condition variables to wait for checkpoints.
Previously we used a polling/sleeping loop to wait for checkpointsto begin and end, which leads to up to a couple hundred millisecondsof needless thumb-twiddling. Use condition variables instead.Author: Thomas MunroReviewed-by: Andres FreundDiscussion:https://postgr.es/m/CA%2BhUKGLY7sDe%2Bbg1K%3DbnEzOofGoo4bJHYh9%2BcDCXJepb6DQmLw%40mail.gmail.com
1 parent5655565 commitc6c9474

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4 files changed

+34
-5
lines changed

4 files changed

+34
-5
lines changed

‎doc/src/sgml/monitoring.sgml

Lines changed: 9 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -1281,7 +1281,7 @@ postgres 27093 0.0 0.0 30096 2752 ? Ss 11:34 0:00 postgres: ser
12811281
<entry>Waiting in an extension.</entry>
12821282
</row>
12831283
<row>
1284-
<entry morerows="34"><literal>IPC</literal></entry>
1284+
<entry morerows="36"><literal>IPC</literal></entry>
12851285
<entry><literal>BgWorkerShutdown</literal></entry>
12861286
<entry>Waiting for background worker to shut down.</entry>
12871287
</row>
@@ -1293,6 +1293,14 @@ postgres 27093 0.0 0.0 30096 2752 ? Ss 11:34 0:00 postgres: ser
12931293
<entry><literal>BtreePage</literal></entry>
12941294
<entry>Waiting for the page number needed to continue a parallel B-tree scan to become available.</entry>
12951295
</row>
1296+
<row>
1297+
<entry><literal>CheckpointDone</literal></entry>
1298+
<entry>Waiting for a checkpoint to complete.</entry>
1299+
</row>
1300+
<row>
1301+
<entry><literal>CheckpointStart</literal></entry>
1302+
<entry>Waiting for a checkpoint to start.</entry>
1303+
</row>
12961304
<row>
12971305
<entry><literal>ClogGroupUpdate</literal></entry>
12981306
<entry>Waiting for group leader to update transaction status at transaction end.</entry>

‎src/backend/postmaster/checkpointer.c

Lines changed: 17 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -126,6 +126,9 @@ typedef struct
126126

127127
intckpt_flags;/* checkpoint flags, as defined in xlog.h */
128128

129+
ConditionVariablestart_cv;/* signaled when ckpt_started advances */
130+
ConditionVariabledone_cv;/* signaled when ckpt_done advances */
131+
129132
uint32num_backend_writes;/* counts user backend buffer writes */
130133
uint32num_backend_fsync;/* counts user backend fsync calls */
131134

@@ -428,6 +431,8 @@ CheckpointerMain(void)
428431
CheckpointerShmem->ckpt_started++;
429432
SpinLockRelease(&CheckpointerShmem->ckpt_lck);
430433

434+
ConditionVariableBroadcast(&CheckpointerShmem->start_cv);
435+
431436
/*
432437
* The end-of-recovery checkpoint is a real checkpoint that's
433438
* performed while we're still in recovery.
@@ -488,6 +493,8 @@ CheckpointerMain(void)
488493
CheckpointerShmem->ckpt_done=CheckpointerShmem->ckpt_started;
489494
SpinLockRelease(&CheckpointerShmem->ckpt_lck);
490495

496+
ConditionVariableBroadcast(&CheckpointerShmem->done_cv);
497+
491498
if (ckpt_performed)
492499
{
493500
/*
@@ -915,6 +922,8 @@ CheckpointerShmemInit(void)
915922
MemSet(CheckpointerShmem,0,size);
916923
SpinLockInit(&CheckpointerShmem->ckpt_lck);
917924
CheckpointerShmem->max_requests=NBuffers;
925+
ConditionVariableInit(&CheckpointerShmem->start_cv);
926+
ConditionVariableInit(&CheckpointerShmem->done_cv);
918927
}
919928
}
920929

@@ -1023,6 +1032,7 @@ RequestCheckpoint(int flags)
10231032
new_failed;
10241033

10251034
/* Wait for a new checkpoint to start. */
1035+
ConditionVariablePrepareToSleep(&CheckpointerShmem->start_cv);
10261036
for (;;)
10271037
{
10281038
SpinLockAcquire(&CheckpointerShmem->ckpt_lck);
@@ -1032,13 +1042,15 @@ RequestCheckpoint(int flags)
10321042
if (new_started!=old_started)
10331043
break;
10341044

1035-
CHECK_FOR_INTERRUPTS();
1036-
pg_usleep(100000L);
1045+
ConditionVariableSleep(&CheckpointerShmem->start_cv,
1046+
WAIT_EVENT_CHECKPOINT_START);
10371047
}
1048+
ConditionVariableCancelSleep();
10381049

10391050
/*
10401051
* We are waiting for ckpt_done >= new_started, in a modulo sense.
10411052
*/
1053+
ConditionVariablePrepareToSleep(&CheckpointerShmem->done_cv);
10421054
for (;;)
10431055
{
10441056
intnew_done;
@@ -1051,9 +1063,10 @@ RequestCheckpoint(int flags)
10511063
if (new_done-new_started >=0)
10521064
break;
10531065

1054-
CHECK_FOR_INTERRUPTS();
1055-
pg_usleep(100000L);
1066+
ConditionVariableSleep(&CheckpointerShmem->done_cv,
1067+
WAIT_EVENT_CHECKPOINT_DONE);
10561068
}
1069+
ConditionVariableCancelSleep();
10571070

10581071
if (new_failed!=old_failed)
10591072
ereport(ERROR,

‎src/backend/postmaster/pgstat.c

Lines changed: 6 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -3623,6 +3623,12 @@ pgstat_get_wait_ipc(WaitEventIPC w)
36233623
caseWAIT_EVENT_BTREE_PAGE:
36243624
event_name="BtreePage";
36253625
break;
3626+
caseWAIT_EVENT_CHECKPOINT_DONE:
3627+
event_name="CheckpointDone";
3628+
break;
3629+
caseWAIT_EVENT_CHECKPOINT_START:
3630+
event_name="CheckpointStart";
3631+
break;
36263632
caseWAIT_EVENT_CLOG_GROUP_UPDATE:
36273633
event_name="ClogGroupUpdate";
36283634
break;

‎src/include/pgstat.h

Lines changed: 2 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -817,6 +817,8 @@ typedef enum
817817
WAIT_EVENT_BGWORKER_STARTUP,
818818
WAIT_EVENT_BTREE_PAGE,
819819
WAIT_EVENT_CLOG_GROUP_UPDATE,
820+
WAIT_EVENT_CHECKPOINT_DONE,
821+
WAIT_EVENT_CHECKPOINT_START,
820822
WAIT_EVENT_EXECUTE_GATHER,
821823
WAIT_EVENT_HASH_BATCH_ALLOCATING,
822824
WAIT_EVENT_HASH_BATCH_ELECTING,

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