Re: Seeking reason behind performance gain in 12 with HashAggregate

From: Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>
To: Shira Bezalel <shira(at)sfei(dot)org>
Cc: Michael Lewis <mlewis(at)entrata(dot)com>, Justin Pryzby <pryzby(at)telsasoft(dot)com>, postgres performance list <pgsql-performance(at)postgresql(dot)org>
Subject: Re: Seeking reason behind performance gain in 12 with HashAggregate
Date: 2020-01-13 21:11:56
Message-ID: 20200113211156.ubllzwzisdyljox5@development
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On Mon, Jan 13, 2020 at 12:44:14PM -0800, Shira Bezalel wrote:
>Hi Michael,
>
>I appreciate your question. I ran a vacuum analyze on the 9.6 table and it
>yielded no difference. Same number of buffers were read, same query plan.
>

VACUUM ANALYZE won't shrink the table - the number of buffers will be
exactly the same. You need to do VACUUM FULL, but be careful as that
acquires exclusive lock on the table.

regards

--
Tomas Vondra http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

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