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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
This commit is contained in:
Thomas Munro 2019-03-14 10:25:27 +13:00
parent 5655565c07
commit c6c9474aaf
4 changed files with 34 additions and 5 deletions
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10
doc/src/sgml/monitoring.sgml
View File

@ -1281,7 +1281,7 @@ postgres 27093 0.0 0.0 30096 2752 ? Ss 11:34 0:00 postgres: ser
<entry>Waiting in an extension.</entry>
</row>
<row>
<entry morerows="34"><literal>IPC</literal></entry>
<entry morerows="36"><literal>IPC</literal></entry>
<entry><literal>BgWorkerShutdown</literal></entry>
<entry>Waiting for background worker to shut down.</entry>
</row>
@ -1293,6 +1293,14 @@ postgres 27093 0.0 0.0 30096 2752 ? Ss 11:34 0:00 postgres: ser
<entry><literal>BtreePage</literal></entry>
<entry>Waiting for the page number needed to continue a parallel B-tree scan to become available.</entry>
</row>
<row>
<entry><literal>CheckpointDone</literal></entry>
<entry>Waiting for a checkpoint to complete.</entry>
</row>
<row>
<entry><literal>CheckpointStart</literal></entry>
<entry>Waiting for a checkpoint to start.</entry>
</row>
<row>
<entry><literal>ClogGroupUpdate</literal></entry>
<entry>Waiting for group leader to update transaction status at transaction end.</entry>

21
src/backend/postmaster/checkpointer.c
View File

@ -126,6 +126,9 @@ typedef struct
int ckpt_flags; /* checkpoint flags, as defined in xlog.h */
ConditionVariable start_cv; /* signaled when ckpt_started advances */
ConditionVariable done_cv; /* signaled when ckpt_done advances */
uint32 num_backend_writes; /* counts user backend buffer writes */
uint32 num_backend_fsync; /* counts user backend fsync calls */
@ -428,6 +431,8 @@ CheckpointerMain(void)
CheckpointerShmem->ckpt_started++;
SpinLockRelease(&CheckpointerShmem->ckpt_lck);
ConditionVariableBroadcast(&CheckpointerShmem->start_cv);
/*
* The end-of-recovery checkpoint is a real checkpoint that's
* performed while we're still in recovery.
@ -488,6 +493,8 @@ CheckpointerMain(void)
CheckpointerShmem->ckpt_done = CheckpointerShmem->ckpt_started;
SpinLockRelease(&CheckpointerShmem->ckpt_lck);
ConditionVariableBroadcast(&CheckpointerShmem->done_cv);
if (ckpt_performed)
{
/*
@ -915,6 +922,8 @@ CheckpointerShmemInit(void)
MemSet(CheckpointerShmem, 0, size);
SpinLockInit(&CheckpointerShmem->ckpt_lck);
CheckpointerShmem->max_requests = NBuffers;
ConditionVariableInit(&CheckpointerShmem->start_cv);
ConditionVariableInit(&CheckpointerShmem->done_cv);
}
}
@ -1023,6 +1032,7 @@ RequestCheckpoint(int flags)
new_failed;
/* Wait for a new checkpoint to start. */
ConditionVariablePrepareToSleep(&CheckpointerShmem->start_cv);
for (;;)
{
SpinLockAcquire(&CheckpointerShmem->ckpt_lck);
@ -1032,13 +1042,15 @@ RequestCheckpoint(int flags)
if (new_started != old_started)
break;
CHECK_FOR_INTERRUPTS();
pg_usleep(100000L);
ConditionVariableSleep(&CheckpointerShmem->start_cv,
WAIT_EVENT_CHECKPOINT_START);
}
ConditionVariableCancelSleep();
/*
* We are waiting for ckpt_done >= new_started, in a modulo sense.
*/
ConditionVariablePrepareToSleep(&CheckpointerShmem->done_cv);
for (;;)
{
int new_done;
@ -1051,9 +1063,10 @@ RequestCheckpoint(int flags)
if (new_done - new_started >= 0)
break;
CHECK_FOR_INTERRUPTS();
pg_usleep(100000L);
ConditionVariableSleep(&CheckpointerShmem->done_cv,
WAIT_EVENT_CHECKPOINT_DONE);
}
ConditionVariableCancelSleep();
if (new_failed != old_failed)
ereport(ERROR,

6
src/backend/postmaster/pgstat.c
View File

@ -3623,6 +3623,12 @@ pgstat_get_wait_ipc(WaitEventIPC w)
case WAIT_EVENT_BTREE_PAGE:
event_name = "BtreePage";
break;
case WAIT_EVENT_CHECKPOINT_DONE:
event_name = "CheckpointDone";
break;
case WAIT_EVENT_CHECKPOINT_START:
event_name = "CheckpointStart";
break;
case WAIT_EVENT_CLOG_GROUP_UPDATE:
event_name = "ClogGroupUpdate";
break;

2
src/include/pgstat.h
View File

@ -817,6 +817,8 @@ typedef enum
WAIT_EVENT_BGWORKER_STARTUP,
WAIT_EVENT_BTREE_PAGE,
WAIT_EVENT_CLOG_GROUP_UPDATE,
WAIT_EVENT_CHECKPOINT_DONE,
WAIT_EVENT_CHECKPOINT_START,
WAIT_EVENT_EXECUTE_GATHER,
WAIT_EVENT_HASH_BATCH_ALLOCATING,
WAIT_EVENT_HASH_BATCH_ELECTING,