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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Michael Lewis <mlewis@entrata.com>
Cc: kimaidou <kimaidou@gmail.com>
Cc: Justin Pryzby <pryzby@telsasoft.com>
Cc: postgres performance list <pgsql-performance@postgresql.org>
Subject: Re: Aggregate and many LEFT JOIN
Date: Fri, 22 Feb 2019 13:05:59 -0500
Message-ID: <17803.1550858759@sss.pgh.pa.us> (raw)
In-Reply-To: <CAHOFxGpHYTTVAdJW1Fi9K3N4P12nF384WyrvwbhgZBYpCMmC2g@mail.gmail.com>
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	<20190222155415.GE28750@telsasoft.com>
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	<CAMKXKO5d8g45qYUtB6FvbQYW4JVEzjUBxN5yJtgvQ+90A0ukBg@mail.gmail.com>
	<CAHOFxGpHYTTVAdJW1Fi9K3N4P12nF384WyrvwbhgZBYpCMmC2g@mail.gmail.com>

Michael Lewis <mlewis@entrata.com> writes:
> Does the plan change significantly with this-
> set session work_mem='250MB';
> set session geqo_threshold = 20;
> set session join_collapse_limit = 20;

Yeah ... by my count there are 16 tables in this query, so raising
join_collapse_limit to 15 is not enough to ensure that the planner
considers all join orders.  Whether use of GEQO is a big problem
is harder to say, but it might be.

			regards, tom lane




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