Re: Slow planning time for simple query

Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> writes:

> Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com> writes:
>
>> 2018-06-06 18:59 GMT+02:00 Jeremy Finzel <finzelj(at)gmail(dot)com>:
>>> We have an odd scenario on one of our OLTP systems, which behaves the same
>>> way on a streamer, of a 700-1000ms planning time for a query like this:
>>> SELECT *
>>> FROM table1
>>> WHERE source_id IN (SELECT id FROM table2 WHERE customer_id = $1);
>
>> more times I seen similar issue based on bloated indexes on table - pg in
>> planning time detect min max from possible indexes
>
> Oh, hmm, yeah it could be ye olde get_actual_variable_range() issue.
> When this happens, are there perhaps a lot of recently-dead rows at either
> extreme of the range of table1.source_id or table2.id?

We noticed the cluster of interest had a rogue physical rep slot holding
71k WAL segments.

Dropping same slot seemed to correlate with the problem going away.

Does that sound like a plausible explanation for the observed slow
planning times?

Thx

> We made a fix last year to improve that:
> https://git.postgresql.org/gitweb/?p=postgresql.git&a=commitdiff&h=3ca930fc3
> but it wasn't back-patched.
>
> regards, tom lane
>
>

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Jerry Sievers
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