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From: Tomas Vondra <tomas.vondra@2ndquadrant.com>
To: Shira Bezalel <shira@sfei.org>
Cc: Michael Lewis <mlewis@entrata.com>
Cc: Justin Pryzby <pryzby@telsasoft.com>
Cc: postgres performance list <pgsql-performance@postgresql.org>
Subject: Re: Seeking reason behind performance gain in 12 with HashAggregate
Date: Mon, 13 Jan 2020 22:11:56 +0100
Message-ID: <20200113211156.ubllzwzisdyljox5@development> (raw)
In-Reply-To: <CAE0KEwHrXdXu8g8_1KJ5efnyS438CpOarxOERfKO4EvKpYcaBw@mail.gmail.com>
References: <CAE0KEwGnDspRJjX=cdvGC69=F=76jbhiViDp=T5pPYR0xF2NAQ@mail.gmail.com>
	<20200113164220.GH26045@telsasoft.com>
	<CAE0KEwF-TZvn-Uar68Vem_jrKxoS=bzxmaBmxmFKFQ555-rg5Q@mail.gmail.com>
	<CAHOFxGo8tXqvsC6=X_SCu-p2_xTb1+xYWWfv3JdcVKnftKjxEQ@mail.gmail.com>
	<CAE0KEwHrXdXu8g8_1KJ5efnyS438CpOarxOERfKO4EvKpYcaBw@mail.gmail.com>

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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