Re: Reaping Temp tables to avoid XID wraparound

On Wed, Feb 13, 2019 at 6:05 PM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:

> Magnus Hagander <magnus(at)hagander(dot)net> writes:
> > And while at it, what would in this particular case have been even more
> > useful to the OP would be to actually identify that there is a temp table
> > *and which xid it's blocking at*. For regular transactions we can look at
> > backend_xid, but IIRC that doesn't work for temp tables (unless they are
> > inside a transaction). Maybe we can find a way to expose that type of
> > relevant information at a similar level while poking around that code?
>
> Maybe I'm confused, but doesn't the table's pg_class row tell you what
> you need to know? You can't look inside another session's temp table,
> but you don't need to.
>

I believe it does, yes.

But that doesn't make for a way to conveniently go "what is it that's
causing waparound problems", since due to pg_class being per database, you
have to loop over all your databases to find that query. Having that
information available in a way that's easy for monitoring to get at (much
as the backend_xid field in pg_stat_activity can help you wrt general
snapshots) would be useful.

--
Magnus Hagander
Me: https://www.hagander.net/ <http://www.hagander.net/>
Work: https://www.redpill-linpro.com/ <http://www.redpill-linpro.com/>