Re: Long running DDL statements blocking all queries

There was too much noise in the pg_stat_activity output, so I did not post
it. I'll collect the output again and post.

But, when I checked in pg_stat_activity, PID 18317 is the session that's
running the ALTER statement and it was showing up as "active". So, it's not
blocked by anything, but the fact that the ALTER statement is long running
and it's blocking the operations that are not even on the same table for
the entire duration it's running is troubling.

Thanks,
Ashu

On Thu, May 31, 2018 at 6:28 PM Fabio Pardi <f(dot)pardi(at)portavita(dot)eu> wrote:

> Ashu,
>
> please, provide full output of:
>
>
> \x
> select * from pg_stat_activity ;
>
>
>
> What you posted on github is only providing a list of blocked backends.
>
> If I read it correctly, then PID 18317 is the root cause of all the locks,
> but it does not show up in the list, not being blocked by anything...
>
>
> regards,
>
> fabio pardi
>
>
>
> On 31/05/18 14:26, Ashu Pachauri wrote:
> > Thanks Fabio for the reply.
> > The queries are blocked in the sense that I can see them in
> pg_stat_activity.
> >
> > Please find the query and its output for correlating the blocked
> activity with blocking query from pg_state_activity and pg_locks:
> https://gist.github.com/ashu210890/c39cd7a38ce37f4baab2f58e1ade1403
> >
> > This output was captured after stopping all writes to our postgres
> database and the only thing talking to postgres was our webserver that only
> does metadata reads. As you can see from the above gist, even the 'SET'
> statements are blocked waiting for the ALTER statement to finish.
> >
> >
> > Thanks,
> > Ashu
> >
> >
> > On Thu, May 31, 2018 at 4:38 PM Fabio Pardi <f(dot)pardi(at)portavita(dot)eu
> <mailto:f(dot)pardi(at)portavita(dot)eu>> wrote:
> >
> > Hi Ashu,
> >
> > when you say 'almost every query in our application starts getting
> blocked'...
> >
> >
> > 'blocked' as in 'they are stuck and can be seen in
> pg_stat_activity'? (in this case, please post the full content of
> pg_stat_activity)
> >
> > or
> >
> > 'blocked' as in 'they are waiting in pgbouncer pool?
> >
> >
> > regards,
> >
> > fabio pardi
> >
> >
> > On 31/05/18 12:38, Ashu Pachauri wrote:
> > > We have been using Postgres 9.5.12 behind PGBouncer and facing
> some weird issues. Whenever we running long running DDL statements (e.g.
> 'add index concurently' or 'Alter table alter column type'), after some
> time, we start seeing that almost every query in our application starts
> getting blocked.
> > > I understand that the operations I mentioned cab be unsafe, but
> the queries being blocked are on completely unrelated tables. I used the
> instructions given on Postgres wiki (
> https://wiki.postgresql.org/wiki/Lock_Monitoring) to correlate the
> blocking and blocked statements and there seems to be absolutely no
> correlation.
> > >
> > > Thanks,
> > > Ashu
> >
>