Use condition variables to wait for checkpoints.
Previously we used a polling/sleeping loop to wait for checkpoints to begin and end, which leads to up to a couple hundred milliseconds of needless thumb-twiddling. Use condition variables instead. Author: Thomas Munro Reviewed-by: Andres Freund Discussion: https://postgr.es/m/CA%2BhUKGLY7sDe%2Bbg1K%3DbnEzOofGoo4bJHYh9%2BcDCXJepb6DQmLw%40mail.gmail.com
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@ -1281,7 +1281,7 @@ postgres 27093 0.0 0.0 30096 2752 ? Ss 11:34 0:00 postgres: ser
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<entry>Waiting in an extension.</entry>
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</row>
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<row>
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<entry morerows="34"><literal>IPC</literal></entry>
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<entry morerows="36"><literal>IPC</literal></entry>
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<entry><literal>BgWorkerShutdown</literal></entry>
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<entry>Waiting for background worker to shut down.</entry>
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</row>
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@ -1293,6 +1293,14 @@ postgres 27093 0.0 0.0 30096 2752 ? Ss 11:34 0:00 postgres: ser
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<entry><literal>BtreePage</literal></entry>
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<entry>Waiting for the page number needed to continue a parallel B-tree scan to become available.</entry>
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</row>
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<row>
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<entry><literal>CheckpointDone</literal></entry>
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<entry>Waiting for a checkpoint to complete.</entry>
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</row>
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<row>
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<entry><literal>CheckpointStart</literal></entry>
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<entry>Waiting for a checkpoint to start.</entry>
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</row>
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<row>
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<entry><literal>ClogGroupUpdate</literal></entry>
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<entry>Waiting for group leader to update transaction status at transaction end.</entry>
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@ -126,6 +126,9 @@ typedef struct
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int ckpt_flags; /* checkpoint flags, as defined in xlog.h */
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ConditionVariable start_cv; /* signaled when ckpt_started advances */
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ConditionVariable done_cv; /* signaled when ckpt_done advances */
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uint32 num_backend_writes; /* counts user backend buffer writes */
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uint32 num_backend_fsync; /* counts user backend fsync calls */
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@ -428,6 +431,8 @@ CheckpointerMain(void)
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CheckpointerShmem->ckpt_started++;
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SpinLockRelease(&CheckpointerShmem->ckpt_lck);
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ConditionVariableBroadcast(&CheckpointerShmem->start_cv);
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/*
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* The end-of-recovery checkpoint is a real checkpoint that's
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* performed while we're still in recovery.
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@ -488,6 +493,8 @@ CheckpointerMain(void)
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CheckpointerShmem->ckpt_done = CheckpointerShmem->ckpt_started;
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SpinLockRelease(&CheckpointerShmem->ckpt_lck);
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ConditionVariableBroadcast(&CheckpointerShmem->done_cv);
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if (ckpt_performed)
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{
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/*
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@ -915,6 +922,8 @@ CheckpointerShmemInit(void)
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MemSet(CheckpointerShmem, 0, size);
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SpinLockInit(&CheckpointerShmem->ckpt_lck);
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CheckpointerShmem->max_requests = NBuffers;
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ConditionVariableInit(&CheckpointerShmem->start_cv);
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ConditionVariableInit(&CheckpointerShmem->done_cv);
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}
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}
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@ -1023,6 +1032,7 @@ RequestCheckpoint(int flags)
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new_failed;
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/* Wait for a new checkpoint to start. */
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ConditionVariablePrepareToSleep(&CheckpointerShmem->start_cv);
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for (;;)
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{
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SpinLockAcquire(&CheckpointerShmem->ckpt_lck);
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@ -1032,13 +1042,15 @@ RequestCheckpoint(int flags)
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if (new_started != old_started)
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break;
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CHECK_FOR_INTERRUPTS();
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pg_usleep(100000L);
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ConditionVariableSleep(&CheckpointerShmem->start_cv,
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WAIT_EVENT_CHECKPOINT_START);
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}
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ConditionVariableCancelSleep();
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/*
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* We are waiting for ckpt_done >= new_started, in a modulo sense.
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*/
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ConditionVariablePrepareToSleep(&CheckpointerShmem->done_cv);
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for (;;)
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{
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int new_done;
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@ -1051,9 +1063,10 @@ RequestCheckpoint(int flags)
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if (new_done - new_started >= 0)
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break;
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CHECK_FOR_INTERRUPTS();
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pg_usleep(100000L);
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ConditionVariableSleep(&CheckpointerShmem->done_cv,
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WAIT_EVENT_CHECKPOINT_DONE);
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}
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ConditionVariableCancelSleep();
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if (new_failed != old_failed)
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ereport(ERROR,
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@ -3623,6 +3623,12 @@ pgstat_get_wait_ipc(WaitEventIPC w)
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case WAIT_EVENT_BTREE_PAGE:
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event_name = "BtreePage";
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break;
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case WAIT_EVENT_CHECKPOINT_DONE:
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event_name = "CheckpointDone";
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break;
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case WAIT_EVENT_CHECKPOINT_START:
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event_name = "CheckpointStart";
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break;
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case WAIT_EVENT_CLOG_GROUP_UPDATE:
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event_name = "ClogGroupUpdate";
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break;
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@ -817,6 +817,8 @@ typedef enum
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WAIT_EVENT_BGWORKER_STARTUP,
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WAIT_EVENT_BTREE_PAGE,
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WAIT_EVENT_CLOG_GROUP_UPDATE,
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WAIT_EVENT_CHECKPOINT_DONE,
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WAIT_EVENT_CHECKPOINT_START,
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WAIT_EVENT_EXECUTE_GATHER,
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WAIT_EVENT_HASH_BATCH_ALLOCATING,
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WAIT_EVENT_HASH_BATCH_ELECTING,
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