Re: shared-memory based stats collector

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.

regards.

--
Kyotaro Horiguchi
NTT Open Source Software Center