Function CheckpointWriteDelay

src/backend/postmaster/checkpointer.c:705–766

* CheckpointWriteDelay -- control rate of checkpoint * * This function is called after each page write performed by BufferSync(). * It is responsible for throttling BufferSync()'s write rate to hit * checkpoint_completion_target. * * The checkpoint request flags should be passed in; currently the only one * examined is CHECKPOINT_IMMEDIATE, which disables delays between writes. * * 'progr

 * fraction between 0.0 meaning none, and 1.0 meaning all done.
 */
void
CheckpointWriteDelay(int flags, double progress)
{
	static int	absorb_counter = WRITES_PER_ABSORB;

	/* Do nothing if checkpoint is being executed by non-checkpointer process */
	if (!AmCheckpointerProcess())
		return;

	/*
	 * Perform the usual duties and take a nap, unless we're behind schedule,
	 * in which case we just try to catch up as quickly as possible.
	 */
	if (!(flags & CHECKPOINT_IMMEDIATE) &&
		!ShutdownRequestPending &&
		!ImmediateCheckpointRequested() &&
		IsCheckpointOnSchedule(progress))
	{
		if (ConfigReloadPending)
		{
			ConfigReloadPending = false;
			ProcessConfigFile(PGC_SIGHUP);
			/* update shmem copies of config variables */
			UpdateSharedMemoryConfig();
		}

		AbsorbSyncRequests();
		absorb_counter = WRITES_PER_ABSORB;

		CheckArchiveTimeout();

		/*
		 * Report interim activity statistics to the stats collector.
		 */
		pgstat_send_bgwriter();

		/*
		 * This sleep used to be connected to bgwriter_delay, typically 200ms.
		 * That resulted in more frequent wakeups if not much work to do.
		 * Checkpointer and bgwriter are no longer related so take the Big
		 * Sleep.
		 */
		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)
	{
		/*
		 * Absorb pending fsync requests after each WRITES_PER_ABSORB write
		 * operations even when we don't sleep, to prevent overflow of the
		 * fsync request queue.
		 */
		AbsorbSyncRequests();
		absorb_counter = WRITES_PER_ABSORB;
	}