| From: | Julien Rouhaud <rjuju123(at)gmail(dot)com> |
|---|---|
| To: | Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com> |
| Cc: | Michael Paquier <michael(at)paquier(dot)xyz>, Sergei Kornilov <sk(at)zsrv(dot)org>, Guillaume Lelarge <guillaume(at)lelarge(dot)info>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org> |
| Subject: | Re: Expose lock group leader pid in pg_stat_activity |
| Date: | 2020-01-28 13:26:34 |
| Message-ID: | CAOBaU_YpsBA2puV8NtjV_Oit2jbt=wnNSA_2E41kGUi_BhA8rA@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Tue, Jan 28, 2020 at 2:09 PM Tomas Vondra
<tomas(dot)vondra(at)2ndquadrant(dot)com> wrote:
>
> I agree a separate "leader_id" column is easier to work with, as it does
> not require unnesting and so on.
>
> As for the consistency, I agree we probably can't make this perfect, as
> we're fetching and processing the PGPROC records one by one. Fixing that
> would require acquiring a much stronger lock on PGPROC, and perhaps some
> other locks. That's pre-existing behavior, of course, it's just not very
> obvious as we don't have any dependencies between the rows, I think.
> Adding the leader_id will change, that, of course. But I think it's
> still mostly OK, even with the possible inconsistency.
There were already some dependencies between the rows since parallel
queries were added, as you could see eg. a parallel worker while no
query is currently active. This patch will make those corner cases
more obvious. Should I document the possible inconsistencies?
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