Re: Show WAL write and fsync stats in pg_stat_io

Hi,

On Mon, 27 Jan 2025 at 03:52, Michael Paquier <michael(at)paquier(dot)xyz> wrote:
>
> On Fri, Jan 24, 2025 at 06:29:46PM +0300, Nazir Bilal Yavuz wrote:
> > By saying that, this does not solve the problem; there is still a
> > difference although you omit WAL initialization stats from the
> > pg_stat_io.
>
> Reattaching the remaining patches to make the cfbot happy, as 0001 has
> been applied as 87a6690cc695.

Thanks!

>
> - if (track_wal_io_timing)
> - {
> - instr_time end;
> -
> - INSTR_TIME_SET_CURRENT(end);
> - INSTR_TIME_ACCUM_DIFF(PendingWalStats.wal_write_time, end, start);
> - }
>
> In 0002, you are removing PendingWalStats.wal_write_time, which does
> not seem OK to me because we should still aggregate this data for
> track_wal_io_timing, no?

We use PendingWalStats.wal_[ write | sync ]_time only to show timings
on the pg_stat_wal view, right? And now these pg_stat_wal.wal_[ write
| sync ]_time datas are fetched from the pg_stat_io view when the
track_wal_io_timing is on. So, I think it is correct to remove these.

I made a mistake while splitting the patches. The places where
'PendingWalStats.wal_[ write | sync ]_time are incremented (the code
piece you shared)' are removed in 0002 (0001 now), but they should be
removed in 0003 (0002 now) instead. This is corrected in v11.

--
Regards,
Nazir Bilal Yavuz
Microsoft