Re: Deadlock between backend and recovery may not be detected

On Tue, Jan 5, 2021 at 3:26 PM Fujii Masao <masao(dot)fujii(at)oss(dot)nttdata(dot)com> wrote:
>
>
>
> On 2020/12/25 13:16, Kyotaro Horiguchi wrote:
> > At Wed, 23 Dec 2020 21:42:47 +0900, Fujii Masao <masao(dot)fujii(at)oss(dot)nttdata(dot)com> wrote in
> >> you. Attached
> >> is the updated of the patch. What about this version?
> >
> > The patch contains a hunk in the following structure.
> >
> > + if (got_standby_lock_timeout)
> > + goto cleanup;
> > +
> > + if (got_standby_deadlock_timeout)
> > + {
> > ...
> > + }
> > +
> > +cleanup:
> >
> > It is eqivalent to
> >
> > + if (!got_standby_lock_timeout && got_standby_deadlock_timeout)
> > + {
> > ...
> > + }
> >
> > Is there any reason for the goto?
>
> Yes. That's because we have the following code using goto.
>
> + /* Quick exit if there's no work to be done */
> + if (!VirtualTransactionIdIsValid(*backends))
> + goto cleanup;
>
>
> Regarding the back-patch, I was thinking to back-patch this to all the
> supported branches. But I found that it's not easy to do that to v9.5
> because v9.5 doesn't have some infrastructure code that this bug fix
> patch depends on. So at least the commit 37c54863cf as the infrastructure
> also needs to be back-patched to v9.5. And ISTM that some related commits
> f868a8143a and 8f0de712c3 need to be back-patched. Probably there might
> be some other changes to be back-patched. Unfortunately they cannot be
> applied to v9.5 cleanly and additional changes are necessary.
>
> This situation makes me feel that I'm inclined to skip the back-patch to v9.5.
> Because the next minor version release is the final one for v9.5. So if we
> unexpectedly introduce the bug to v9.5 by the back-patch, there is no
> chance to fix that. OTOH, of course, if we don't do the back-patch, there is
> no chance to fix the deadlock detection bug since the final minor version
> for v9.5 doesn't include that bug fix. But I'm afraid that the back-patch
> to v9.5 may give more risk than gain.
>
> Thought?

+1 for not-backpatching to 9.5.

Regards,

--
Masahiko Sawada
EnterpriseDB: https://www.enterprisedb.com/