Re: Fwd: [BUG]: the walsender does not update its IO statistics until it exits

Hi,

On Tue, Mar 18, 2025 at 07:14:12PM +0800, Xuneng Zhou wrote:
> Hi,
> 
> I performed some tests using elog

Thanks for the testing!

> (no so sure whether this is the proper way
> to do it) to monitor the new method.

Well that simple enough and that works well if the goal is just to "count" ;-)

> Here are the findings:
> 
> • With PGSTAT_MIN_INTERVAL set to 1000ms, the number of flush reports was
> reduced to approximately 40–50 during the installcheck test suite.
> 
> • With PGSTAT_IDLE_INTERVAL set to 10000ms, the reports dropped to fewer
> than 5.
> 
> • In contrast, the previous approach—flushing after every
> WalSndKeepaliveIfNecessary()—resulted in roughly 50,000 flushes.
> 
> This reduction is significant, so the overhead from the flush reports is no
> longer a concern.

Yeah I did observe and do think the same.

> However, we still need to determine whether this
> frequency is sufficient to capture the system’s state during periods of
> high WAL activity.

I think that reporting at PGSTAT_MIN_INTERVAL is fine and more than enough. I
mean, I 'm not sure that there is a real use case to query the statistics related
view at more than a second interval anyway. Or are you concerned that we may not
enter the "When the WAL sender is caught up or has pending data to send" frequently
enough?

> Based on my tests, using PGSTAT_MIN_INTERVAL seems to
> provide a better balance than PGSTAT_IDLE_INTERVAL.

Same here.

Regards,

-- 
Bertrand Drouvot
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com