| From: | Thomas Munro <thomas(dot)munro(at)gmail(dot)com> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | Michael Paquier <michael(at)paquier(dot)xyz>, Postgres hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org> |
| Subject: | Re: Race conditions with checkpointer and shutdown |
| Date: | 2019-04-17 23:39:16 |
| Message-ID: | CA+hUKGJMA=hyQrZciEm-muYzYM-w1mkR9yWGCVq4Hjg2EBbZOQ@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Wed, Apr 17, 2019 at 10:45 AM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> I think what we need to look for is reasons why (1) the postmaster
> never sends SIGUSR2 to the checkpointer, or (2) the checkpointer's
> main loop doesn't get to noticing shutdown_requested.
>
> A rather scary point for (2) is that said main loop seems to be
> assuming that MyLatch a/k/a MyProc->procLatch is not used for any
> other purposes in the checkpointer process. If there were something,
> like say a condition variable wait, that would reset MyLatch at any
> time during a checkpoint, then we could very easily go to sleep at the
> bottom of the loop and not notice that there's a pending shutdown request.
Agreed on the non-composability of that coding, but if there actually
is anything in that loop that can reach ResetLatch(), it's well
hidden...
--
Thomas Munro
https://enterprisedb.com
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