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From: Ian Lawrence Barwick <barwick@gmail.com>
Date: Fri, 25 Aug 2023 09:36:18 +0900
Message-ID: <CAB8KJ=iWYvB1odjFRZybsPeUV8HUAiVVjY9RMHSdvWy1t77cLg@mail.gmail.com>
Subject: Re: pg_stat_get_backend_subxact() and backend IDs?
To: Nathan Bossart <nathandbossart@gmail.com>
Cc: pgsql-hackers <pgsql-hackers@postgresql.org>, robertmhaas@gmail.com
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2023=E5=B9=B48=E6=9C=8825=E6=97=A5(=E9=87=91) 1:19 Nathan Bossart <nathandb=
ossart@gmail.com>:
>
> On Wed, Aug 23, 2023 at 07:51:40PM -0700, Nathan Bossart wrote:
> > On Wed, Aug 23, 2023 at 07:32:06PM -0700, Nathan Bossart wrote:
> >> On Thu, Aug 24, 2023 at 10:22:49AM +0900, Ian Lawrence Barwick wrote:
> >>> Looking at the code, this is happening because
> >>> "pgstat_fetch_stat_local_beentry()"
> >>> expects to be passed the backend ID as an integer representing a 1-ba=
sed index
> >>> referring to "localBackendStatusTable", but "pg_stat_get_backend_subx=
act()"
> >>> is presumably intended to take the actual BackendId , as per other
> >>> "pg_stat_get_XXX()"
> >>> functions.
> >>
> >> Yes, this was changed in d7e39d7, but 10ea0f9 seems to have missed the
> >> memo.
> >
> > BTW I'd argue that this is a bug in v16 that we should try to fix befor=
e
> > GA, so I've added an open item [0].  I assigned it to Robert (CC'd) sin=
ce
> > he was the committer, but I'm happy to pick it up.
>
> Since RC1 is fast approaching, I put together a revised patch set.  0001
> renames the existing pgstat_fetch_stat* functions, and 0002 adds
> pgstat_get_local_beentry_by_backend_id() and uses it for
> pg_stat_get_backend_subxact().  Thoughts?

Thanks for looking at this. In summary we now have these functions:

 extern PgBackendStatus      *pgstat_get_beentry_by_backend_id(BackendId be=
id);
 extern LocalPgBackendStatus
*pgstat_get_local_beentry_by_backend_id(BackendId beid);
 extern LocalPgBackendStatus *pgstat_get_local_beentry_by_index(int beid);

which LGTM; patches work as expected and resolve the reported issue.

Regards

Ian Barwick