Re: possible memory leak in VACUUM ANALYZE

Hi,

On 2023-02-11 00:53:48 -0600, Justin Pryzby wrote:
> On Sat, Feb 11, 2023 at 07:06:45AM +0100, Pavel Stehule wrote:
> > pá 10. 2. 2023 v 23:01 odesílatel Justin Pryzby <pryzby(at)telsasoft(dot)com> napsal:
> > > On Fri, Feb 10, 2023 at 09:23:11PM +0100, Pavel Stehule wrote:
> > > > pá 10. 2. 2023 v 21:18 odesílatel Andres Freund <andres(at)anarazel(dot)de> napsal:
> > > > > On 2023-02-10 21:09:06 +0100, Pavel Stehule wrote:
> > > > > > Just a small note - I executed VACUUM ANALYZE on one customer's database,
> > > > > > and I had to cancel it after a few hours, because it had more than 20GB RAM
> > > > > > (almost all physical RAM).
> > > > >
> > > > > Just to make sure: You're certain this was an actual memory leak, not just
> > > > > vacuum ending up having referenced all of shared_buffers? Unless you use huge
> > > > > pages, RSS increases over time, as a process touched more and more pages in
> > > > > shared memory. Of course that couldn't explain rising above
> > > > > shared_buffers + overhead.
> > > > >
> > > > > > The memory leak is probably not too big. This database is a little bit
> > > > > > unusual. This one database has more than 1 800 000 tables. and the same
> > > > > > number of indexes.
> > > > >
> > > > > If you have 1.8 million tables in a single database, what you saw might just
> > > > > have been the size of the relation and catalog caches.
> > > >
> > > > can be
> > >
> > > Well, how big was shared_buffers on that instance ?
> >
> > 20GB RAM
> > 20GB swap
> > 2GB shared buffers
>
> Thanks; so that can't explain using more than 2GB + a bit of overhead.

I think my theory of 1.8 million relcache / catcache entries is pretty good...

I'd do the vacuum analyze again, interrupt once memory usage is high, and
check
SELECT * FROM pg_backend_memory_contexts ORDER BY total_bytes DESC

> BTW I'm interested about this because I have an VM instance running v15
> which has been killed more than a couple times in the last 6 months, and
> I haven't been able to diagnose why. But autovacuum/analyze could
> explain it. On this one particular instance, we don't have many
> relations, though...

Killed in what way? OOM?

If you'd set up strict overcommit you'd get a nice memory dump in the log...

Greetings,

Andres Freund