Re: elog.c query_id support vs shutdown

Hi,

On 2021-08-08 11:53:39 -0700, Andres Freund wrote:
> On 2021-08-08 13:46:39 +0800, Julien Rouhaud wrote:
> > > I suspect that to make the elog.c usage safe, we'll have to clear MyBEEntry in
> > > pgstat_beshutdown_hook().
> >
> > I agree, and a quick test indeed fix your scenario. It also seems like a good
> > thing to do overall.
>
> Yea, it does seem like a good thing. But we should do a search for the
> problems it could cause...

Not a problem with unsetting MyBEEntry. But the search for problems made me
reread the following comment:

/*
* There's no need for a lock around pgstat_begin_read_activity /
* pgstat_end_read_activity here as it's only called from
* pg_stat_get_activity which is already protected, or from the same
* backend which means that there won't be concurrent writes.
*/

I don't understand the pg_stat_get_activity() part of this comment?
pgstat_get_my_query_id() hardcodes MyBEEntry->st_query_id, so it can't be
useful to pg_stat_get_activity(), nor is it used there?

I assume it's just a remnant from an earlier iteration of the code?

Greetings,

Andres Freund