Re: pg_stat_io for the startup process

At Fri, 28 Apr 2023 11:15:51 +0900 (JST), Kyotaro Horiguchi <horikyota(dot)ntt(at)gmail(dot)com> wrote in
> At Thu, 27 Apr 2023 17:30:40 -0400, Melanie Plageman <melanieplageman(at)gmail(dot)com> wrote in
> > After a quick example implementation of this, I found that it seemed to
> > try and flush the stats less often on an idle standby (good) than using
> > enable_timeout_every().
>
> Just rearming with the full-interval will work that way. Our existing
> strategy for this is seen in PostgresMain().
>
> stats_timeout = pgstat_report_stat(false);
> if (stats_timeout > 0)
> {
> if (!get_timeout_active(BLAH_TIMEOUT))
> enable_timeout_after(BLAH_TIMEOUT, stats_timeout);
> }
> else
> {
> if (get_timeout_active(BLAH_TIMEOUT))
> disable_timeout(BLAH_TIMEOUT, false);
> }
> WaitLatch();

Im my example, I left out idle-time flushing, but I realized we don't
need the timeout mechanism here since we're already managing it. So
the following should work (assuming the timestamp updates with
GetCurrentTimestamp() in my last patch).

@@ -3889,13 +3900,23 @@ WaitForWALToBecomeAvailable(XLogRecPtr RecPtr, bool randAccess,
/* Update pg_stat_recovery_prefetch before sleeping. */
XLogPrefetcherComputeStats(xlogprefetcher);

+ /*
+ * Report stats; if not time yet, set next WaitLatch to
+ * wake up at the next reporing time.
+ */
+ wait_time = pgstat_report_stat(false);
+
+ /* if no pending stats, sleep forever */
+ if (wait_time == 0)
+ wait_time = -1L;
+
/*
* Wait for more WAL to arrive, when we will be woken
* immediately by the WAL receiver.
*/
(void) WaitLatch(&XLogRecoveryCtl->recoveryWakeupLatch,
WL_LATCH_SET | WL_EXIT_ON_PM_DEATH,
- -1L,
+ wait_time,
WAIT_EVENT_RECOVERY_WAL_STREAM);

regards.

--
Kyotaro Horiguchi
NTT Open Source Software Center