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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 a56e7b6601
commit 5e6368b42e
4 changed files with 15 additions and 1 deletions
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8
src/backend/postmaster/checkpointer.c
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@ -484,6 +484,9 @@ 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. */
@ -726,7 +729,10 @@ 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)
{