Re: PostgreSQL hot standby Hangs due to AccessExclusiveLock on pg_attribute or pg_type tables

At Tue, 11 Jul 2017 16:48:11 -0400, Bruno Richard <bruno(dot)richard(at)broadsign(dot)com> wrote in <CAB-EU3St=O+FoXt-i8OkCp3A36Xft6TTOX6DO1okp=0Ub47n5w(at)mail(dot)gmail(dot)com>
> Thanks for the replies.
>
> Jeff, there were no long-lived transactions in pg_stat_activity while
> pg_attribute was locked. We were able to query it from another database on
> the same instance.
>
> I can't say if it would correct after 20 minutes since it causes us major
> issues in our application.
>
> Five days ago, we tried the hot_standy_feedback=on setting on one of our
> hot standbys and we don't get locks anymore. We even don't get locks from
> hot standbys not having the setting enabled.

That's because a feedback from a standby prevents vacuum on the
master from emitting WAL records
possiblly-conflicts-with-all-standbys at the time. So a low
chance to see the locks was still remaining.

> We will enable it on those later this week.

This can eliminate the remaining chance.

regards,

--
Kyotaro Horiguchi
NTT Open Source Software Center