Re: Weird planner issue on a standby

Le mar. 11 oct. 2022 à 19:42, Guillaume Lelarge <guillaume(at)lelarge(dot)info> a
écrit :

> Le mar. 11 oct. 2022 à 18:27, Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org> a
> écrit :
>
>> On 2022-Oct-11, Tom Lane wrote:
>>
>> > Are there any tables in this query where extremal values of the join
>> > key are likely to be in recently-added or recently-dead rows? Does
>> > VACUUM'ing on the primary help?
>>
>> I remember having an hypothesis, upon getting a report of this exact
>> problem on a customer system once, that it could be due to killtuple not
>> propagating to standbys except by FPIs. I do not remember if we proved
>> that true or not. I do not remember observing that tables were being
>> read, however.
>>
>>
> Thanks for your answers.
>
> The last predicate is "and c3>='2020-10-10' and c3<='2022-10-10'. I have
> no idea on the actual use of c3 but rows with c3 at '2022-10-10' (which is
> yesterday) is much probably recently-added. I can ask my customer if you
> want but this looks like a pretty safe bet.
>
> On the VACUUM question, I didn't say, but we're kind of wondering if it
> was lacking a recent-enough VACUUM. So they're doing a VACUUM tonight on
> the database (and especially on the 1.6TB table which is part of the
> query). I'm kind of skeptical because if the VACUUM wasn't enough on the
> standby, it should be the same on the primary.
>
>
It appears that I was wrong. I just got an email from my customer saying
they got their performance back after a VACUUM on the two main tables of
the query. I'll have them on the phone in about an hour. I'll probably know
more then. Still wondering why it was an issue on the standby and not on
the primary. VACUUM cleans up tables and indexes, and this activity goes
through WAL, doesn't it?

--
Guillaume.