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Commit78c0f85

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Wake up for latches in CheckpointWriteDelay().
The checkpointer shouldn't ignore its latch. Other backends may bewaiting for it to drain the request queue. Hopefully real systems don'thave a full queue often, but the condition is reached easily whenshared_buffers is small.This involves defining a new wait event, which will appear in thepg_stat_activity view often due to spread checkpoints.Back-patch only to 14. Even though the problem exists in earlierbranches too, it's hard to hit there. In 14 we stopped using signalhandlers for latches on Linux, *BSD and macOS, which were previouslyhiding this problem by interrupting the sleep (though not reliably, asthe signal could arrive before the sleep begins; precisely the problemlatches 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
1 parentd9f7ad5 commit78c0f85

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4 files changed

+16
-2
lines changed

4 files changed

+16
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lines changed

‎doc/src/sgml/monitoring.sgml‎

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

‎src/backend/postmaster/checkpointer.c‎

Lines changed: 7 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -490,6 +490,9 @@ CheckpointerMain(void)
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}
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ckpt_active= false;
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/* We may have received an interrupt during the checkpoint. */
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HandleCheckpointerInterrupts();
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}
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/* Check for archive_timeout and switch xlog files if necessary. */
@@ -732,7 +735,10 @@ CheckpointWriteDelay(int flags, double progress)
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* Checkpointer and bgwriter are no longer related so take the Big
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* Sleep.
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*/
735-
pg_usleep(100000L);
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WaitLatch(MyLatch,WL_LATCH_SET |WL_EXIT_ON_PM_DEATH |WL_TIMEOUT,
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100,
740+
WAIT_EVENT_CHECKPOINT_WRITE_DELAY);
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ResetLatch(MyLatch);
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}
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elseif (--absorb_counter <=0)
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{

‎src/backend/utils/activity/wait_event.c‎

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Original file line numberDiff line numberDiff line change
@@ -473,6 +473,9 @@ pgstat_get_wait_timeout(WaitEventTimeout w)
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caseWAIT_EVENT_BASE_BACKUP_THROTTLE:
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event_name="BaseBackupThrottle";
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break;
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caseWAIT_EVENT_CHECKPOINT_WRITE_DELAY:
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event_name="CheckpointWriteDelay";
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break;
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caseWAIT_EVENT_PG_SLEEP:
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event_name="PgSleep";
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break;

‎src/include/utils/wait_event.h‎

Lines changed: 2 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -140,7 +140,8 @@ typedef enum
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WAIT_EVENT_PG_SLEEP,
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WAIT_EVENT_RECOVERY_APPLY_DELAY,
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WAIT_EVENT_RECOVERY_RETRIEVE_RETRY_INTERVAL,
143-
WAIT_EVENT_VACUUM_DELAY
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WAIT_EVENT_VACUUM_DELAY,
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WAIT_EVENT_CHECKPOINT_WRITE_DELAY
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}WaitEventTimeout;
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/* ----------

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