Lots of stuck queries after upgrade to 9.4, possible race condition

I forward here from PG general list. Stack traces included.

---------- Forwarded message ----------
From: Spiros Ioannou <sivann(at)inaccess(dot)com>
Date: 20 July 2015 at 13:16
Subject: Re: [GENERAL] Lots of stuck queries after upgrade to 9.4
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: "pgsql-general(at)postgresql(dot)org" <pgsql-general(at)postgresql(dot)org>

Hi Tom,
thank you for your input. The DB was stuck again, I attach all logs and
stack traces.

A stack trace from a COMMIT, an INSERT, an UPDATE, the wal writer, the
writer, and a sequence.

Stracing the commit was stuck at: semop(3145761, {{12, -1, 0}}, 1

Please tell me what else could I do to help debugging.

Is there a way to downgrade postgresql ?

*Spiros Ioannou IT Manager, inAccesswww.inaccess.com
<http://www.inaccess.com>M: +30 6973-903808T: +30 210-6802-358*

On 20 July 2015 at 01:01, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:

> Spiros Ioannou <sivann(at)inaccess(dot)com> writes:
> > We upgraded to 9.4.4 from 8.4 We have tried 9.3.x in the past with
> success.
> > Unfortunately in 9.4 gets stuck 2-3 times a week.
>
> > Lots of queries seem stuck, that is they have waiting:false. Queries can
> be
> > COMMIT or INSERT.
> > No blocking locks seem to exist.
> > strace reveals that all stuck processes they are in semop
> > semop(2064417, {{0, -1, 0}}, 1^C <unfinished ...>
>
> Stack traces of the stuck processes might help determine what's going on.
>
>
> https://wiki.postgresql.org/wiki/Generating_a_stack_trace_of_a_PostgreSQL_backend
>
> Please try to capture traces for both the COMMIT and INSERT cases,
> as they're almost certainly different.
>
> regards, tom lane
>