Re: Extremely slow HashAggregate in simple UNION query

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Jeff Janes <jeff(dot)janes(at)gmail(dot)com>
Cc: Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>, Felix Geisendörfer <felix(at)felixge(dot)de>, "pgsql-performa(dot)" <pgsql-performance(at)postgresql(dot)org>
Subject: Re: Extremely slow HashAggregate in simple UNION query
Date: 2019-08-24 19:41:03
Message-ID: 6839.1566675663@sss.pgh.pa.us
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Jeff Janes <jeff(dot)janes(at)gmail(dot)com> writes:
> Most of the time is not after the clock stops, but before the stepwise
> ANALYZE clock starts. If you just do an EXPLAIN rather than EXPLAIN
> ANALYZE, that is also slow. The giant hash table is created during the
> planning step (or somewhere around there

It's in executor startup, I believe.

regards, tom lane

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