From: Tom Lane <tgl@sss.pgh.pa.us>
To: a.schnabl@synedra.com
Cc: pgsql-bugs@lists.postgresql.org
Subject: Re: BUG #16993: Query Planner does not use index for EXISTS-query on a large table with all equal foreign key values
Date: Wed, 05 May 2021 10:31:10 -0400
Message-ID: <4016383.1620225070@sss.pgh.pa.us> (raw)
In-Reply-To: <16993-1298e8dc9c41ab97@postgresql.org>
References: <16993-1298e8dc9c41ab97@postgresql.org>
PG Bug reporting form <noreply@postgresql.org> writes:
> ... EXPLAIN ANALYZE shows the following query plan:
> Merge Join (cost=179053.41..179054.24 rows=1 width=8) (actual
> time=2140.820..2140.822 rows=1 loops=1)
> [ but with ] SET enable_seqscan = false:
> Nested Loop Semi Join (cost=0.57..12.85 rows=1 width=8) (actual
> time=0.877..0.920 rows=1 loops=1)
Yeah, that seems *extremely* broken. The planner correctly estimates
the second plan as much cheaper, so why did it fail to choose that one
without help? Will look into this.
regards, tom lane
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To: pgsql-bugs@postgresql.org
Cc: tgl@sss.pgh.pa.us, a.schnabl@synedra.com, pgsql-bugs@lists.postgresql.org
Subject: Re: BUG #16993: Query Planner does not use index for EXISTS-query on a large table with all equal foreign key values
In-Reply-To: <4016383.1620225070@sss.pgh.pa.us>
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