Re: Highly Variable Planning Times

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Michael Malis <michaelmalis2(at)gmail(dot)com>
Cc: Pg Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Highly Variable Planning Times
Date: 2017-04-19 20:58:38
Message-ID: 30419.1492635518@sss.pgh.pa.us
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Michael Malis <michaelmalis2(at)gmail(dot)com> writes:
> I've been encountering highly variable planning time on PG 9.5.4.
> Running `EXPLAIN SELECT * FROM events_1171738` will take anywhere from
> 200ms to 4s. This likely has to do with the table having 1300 partial
> indexes on it (for reasons elaborated on in
> https://blog.heapanalytics.com/running-10-million-postgresql-indexes-in-production/)

TBH, I see no convincing explanation in that article of why 1300 partial
indexes are a good idea. *At best*, you're doing substantial work in the
planner to avoid the first tree descent step or two in a single
non-partial index. At worst, all your savings go out the window during a
relcache flush, which is likely to happen whenever a vacuum or analyze
gets done on the underlying table.

regards, tom lane

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