Re: PG12 autovac issues

On Mon, Mar 23, 2020 at 10:40:39PM -0700, Andres Freund wrote:
> On 2020-03-24 14:26:06 +0900, Michael Paquier wrote:
>> Nothing really fancy:
>> - autovacuum_vacuum_cost_delay to 2ms (default of v12, but we used it
>> in v11 as well).
>> - autovacuum_naptime = 15s
>> - autovacuum_max_workers = 6
>> - log_autovacuum_min_duration = 0
>
> Oh, so you're also involved in this? I'm starting to get a bit confused
> as to who is reporting what.

Yeah, sort of. Julien has done a lot of work on that and I have an
access to the data and test beds, so we are just saying the same
things.

> Well, there's no logging of autovacuum launchers that don't do anything
> due to the "skipping redundant" logic, with normal log level. If somehow
> the horizon logic of autovacuum workers gets out of whack with what
> vacuumlazy.c does, then you'd not get any vacuums. But a usage level
> triggered analyze could still happen on such a table, I think.

What surprised me the most is that the same table happened to be
analyzed again and again after the launcher began its blackout.

> While looking at this issue I found a few problems, btw. That seems more
> like a -hackers discussion, so I started:
> https://postgr.es/m/20200323235036.6pje6usrjjx22zv3%40alap3.anarazel.de

Yes, let's discuss there.

> I think I might just have figured out another one...

Ouch.
--
Michael