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Wake up for latches in CheckpointWriteDelay().

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The checkpointer shouldn't ignore its latch.  Other backends may be
waiting for it to drain the request queue.  Hopefully real systems don't
have a full queue often, but the condition is reached easily when
shared_buffers is small.

This involves defining a new wait event, which will appear in the
pg_stat_activity view often due to spread checkpoints.

Back-patch only to 14.  Even though the problem exists in earlier
branches too, it's hard to hit there.  In 14 we stopped using signal
handlers for latches on Linux, *BSD and macOS, which were previously
hiding this problem by interrupting the sleep (though not reliably, as
the signal could arrive before the sleep begins; precisely the problem
latches address).

Reported-by: Andres Freund <andres@anarazel.de>
Reviewed-by: Andres Freund <andres@anarazel.de>
Discussion: https://postgr.es/m/20220226213942.nb7uvb2pamyu26dj%40alap3.anarazel.de
This commit is contained in:
Thomas Munro 2022-03-16 13:37:58 +13:00
parent d9f7ad54e5
commit 78c0f85e43
4 changed files with 16 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
doc/src/sgml/monitoring.sgml
View File

@ -2223,6 +2223,10 @@ postgres 27093 0.0 0.0 30096 2752 ? Ss 11:34 0:00 postgres: ser
<entry><literal>BaseBackupThrottle</literal></entry>
<entry>Waiting during base backup when throttling activity.</entry>
</row>
<row>
<entry><literal>CheckpointerWriteDelay</literal></entry>
<entry>Waiting between writes while performing a checkpoint.</entry>
</row>
<row>
<entry><literal>PgSleep</literal></entry>
<entry>Waiting due to a call to <function>pg_sleep</function> or

8
src/backend/postmaster/checkpointer.c
View File

@ -490,6 +490,9 @@ CheckpointerMain(void)
}
ckpt_active = false;
/* We may have received an interrupt during the checkpoint. */
HandleCheckpointerInterrupts();
}
/* Check for archive_timeout and switch xlog files if necessary. */
@ -732,7 +735,10 @@ CheckpointWriteDelay(int flags, double progress)
* Checkpointer and bgwriter are no longer related so take the Big
* Sleep.
*/
pg_usleep(100000L);
WaitLatch(MyLatch, WL_LATCH_SET | WL_EXIT_ON_PM_DEATH | WL_TIMEOUT,
100,
WAIT_EVENT_CHECKPOINT_WRITE_DELAY);
ResetLatch(MyLatch);
}
else if (--absorb_counter <= 0)
{

3
src/backend/utils/activity/wait_event.c
View File

@ -473,6 +473,9 @@ pgstat_get_wait_timeout(WaitEventTimeout w)
case WAIT_EVENT_BASE_BACKUP_THROTTLE:
event_name = "BaseBackupThrottle";
break;
case WAIT_EVENT_CHECKPOINT_WRITE_DELAY:
event_name = "CheckpointWriteDelay";
break;
case WAIT_EVENT_PG_SLEEP:
event_name = "PgSleep";
break;

3
src/include/utils/wait_event.h
View File

@ -140,7 +140,8 @@ typedef enum
WAIT_EVENT_PG_SLEEP,
WAIT_EVENT_RECOVERY_APPLY_DELAY,
WAIT_EVENT_RECOVERY_RETRIEVE_RETRY_INTERVAL,
WAIT_EVENT_VACUUM_DELAY
WAIT_EVENT_VACUUM_DELAY,
WAIT_EVENT_CHECKPOINT_WRITE_DELAY
} WaitEventTimeout;
/* ----------