From: Tom Lane <tgl@sss.pgh.pa.us>
To: Stephen Cresswell <pgsql-performance@stephen-cresswell.net>
cc: pgsql-performance@postgresql.org
Subject: Re: Why is the optimiser choosing a sub-optimal plan?
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Comments: In-reply-to Stephen Cresswell
 <pgsql-performance@stephen-cresswell.net>
	message dated "Mon, 14 Nov 2016 17:53:43 +0000"
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Date: Mon, 14 Nov 2016 14:37:21 -0500
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Stephen Cresswell <pgsql-performance@stephen-cresswell.net> writes:
> I have the a table with two indexes...

(1) Tell us about the other table, mobile_summary_type.

(2) Did you transcribe the second query plan correctly?  I have a hard
time believing that EXPLAIN printed two Index Cond lines for the same
indexscan.

(3) What PG version is this, exactly?

(4) Are you doing anything funny like disabling autovacuum/autoanalyze?
The rowcount estimates in the "good" plan seem rather far away from
reality, and it's not obvious why, particularly here:

>               ->  Seq Scan on mobile_summary_type mst
> (cost=0.00..18.80 rows=880 width=64) (actual time=0.014..0.016 rows=4
> loops=1)

			regards, tom lane


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