From a9344bb2fb2a363bec4be526f87560cb212ca10b Mon Sep 17 00:00:00 2001 From: Thomas Munro Date: Mon, 28 Feb 2022 11:27:05 +1300 Subject: [PATCH v2 1/3] Wake up for latches in CheckpointWriteDelay(). 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 very 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 Discussion: https://postgr.es/m/20220226213942.nb7uvb2pamyu26dj%40alap3.anarazel.de --- doc/src/sgml/monitoring.sgml | 4 ++++ src/backend/postmaster/checkpointer.c | 8 +++++++- src/backend/utils/activity/wait_event.c | 3 +++ src/include/utils/wait_event.h | 1 + 4 files changed, 15 insertions(+), 1 deletion(-) diff --git a/doc/src/sgml/monitoring.sgml b/doc/src/sgml/monitoring.sgml index 9fb62fec8e..8620aaddc7 100644 --- a/doc/src/sgml/monitoring.sgml +++ b/doc/src/sgml/monitoring.sgml @@ -2235,6 +2235,10 @@ postgres 27093 0.0 0.0 30096 2752 ? Ss 11:34 0:00 postgres: ser BaseBackupThrottle Waiting during base backup when throttling activity. + + CheckpointerWriteDelay + Waiting between writes while performing a checkpoint. + PgSleep Waiting due to a call to pg_sleep or diff --git a/src/backend/postmaster/checkpointer.c b/src/backend/postmaster/checkpointer.c index 4488e3a443..a59c3cf020 100644 --- a/src/backend/postmaster/checkpointer.c +++ b/src/backend/postmaster/checkpointer.c @@ -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) { diff --git a/src/backend/utils/activity/wait_event.c b/src/backend/utils/activity/wait_event.c index 60972c3a75..0706e922b5 100644 --- a/src/backend/utils/activity/wait_event.c +++ b/src/backend/utils/activity/wait_event.c @@ -485,6 +485,9 @@ 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; diff --git a/src/include/utils/wait_event.h b/src/include/utils/wait_event.h index 395d325c5f..d0345c6b49 100644 --- a/src/include/utils/wait_event.h +++ b/src/include/utils/wait_event.h @@ -141,6 +141,7 @@ typedef enum typedef enum { WAIT_EVENT_BASE_BACKUP_THROTTLE = PG_WAIT_TIMEOUT, + WAIT_EVENT_CHECKPOINT_WRITE_DELAY, WAIT_EVENT_PG_SLEEP, WAIT_EVENT_RECOVERY_APPLY_DELAY, WAIT_EVENT_RECOVERY_RETRIEVE_RETRY_INTERVAL, -- 2.30.2