Re: shared-memory based stats collector

At Wed, 04 Nov 2020 17:39:10 +0900 (JST), Kyotaro Horiguchi <horikyota(dot)ntt(at)gmail(dot)com> wrote in
> At Fri, 30 Oct 2020 15:00:55 +0000, Georgios Kokolatos <gkokolatos(at)protonmail(dot)com> wrote in
> > Hi,
> >
> > I noticed that according to the cfbot this patch no longer applies.
> >
> > As it is registered in the upcoming commitfest, it would be appreciated
> > if you could rebase it.
>
> Thanks! The replication slot stats patch (9868167500) hit this.
>
> - Fixed a bug of original code.
>
> get_stat_entry() returned a wrong result to found when shared entry
> exists but it is not locally cached.
>
> - Moved replication slot stats into shared memory stats.
>
> Differently from wal_stats and slru_stats, it can be implemented as a
> part of unified stats entry. I'm tempted to remove the entry for a
> dropped slot immediately, but I didn't that since the number of the
> slots should be under 10 or so and dropping an entry requires
> exclusive lock on dshash. Instead, dropped entries are removed at
> file-write time that happens only at the end of a process.
>
>
> I had to clean up replication slots in pgstat_beshutdown_hook(). Even
> though we have exactly the same code in several other places, the
> function must be called before disabling DSA because we cannot update
> statistics after detaching the shared-memory stats. Perhaps we can
> remove some of the existing calling to ReplicationSlotCleanup() but I
> haven't do that in this version.

Fixed a bug that pgstat_report_replslot fails to reuse entries that
are marked as "dropped".

Fixed comments for the caller sites to pgstat_report_replslot(_drop)
in ReplicationSlotCreate() and ReplicationSlotDropPtr().

regards.

--
Kyotaro Horiguchi
NTT Open Source Software Center