Date: Mon, 24 Sep 2018 21:19:54 -0500
From: Justin Pryzby <pryzby@telsasoft.com>
To: Vladimir Ryabtsev <greatvovan@gmail.com>
Cc: f.pardi@portavita.eu, pgsql-performance@lists.postgresql.org
Subject: Re: Why could different data in a table be processed with different
 performance?
Message-ID: <20180925021954.GW2471@telsasoft.com>
References: 
 <CAMqTPq=aFwfiqv=P9EDs+UxeOgfe03kyQ0uvtUHvSxvfSvYR+w@mail.gmail.com>
 <4dbb8bea-bea3-74d8-a537-36bb9864cb9f@portavita.eu>
 <CAMqTPqkMDEkvx7jUquUCCkwgwYdcS-byzimjap2osxYWqp1KjA@mail.gmail.com>
 <e8d93055-9643-0ad2-d8bd-3f4fc344bf51@portavita.eu>
 <CAMqTPqnUB54YXQutPKPWdoUKEZOnV58WndfTvZagrNLiTr6RHw@mail.gmail.com>
 <20180924233423.GV2471@telsasoft.com>
 <CAMqTPq=f2fQ8tnUu3UxrvfogiDCn+04HWFX8fpZkDoeYQ7ktTQ@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: 
 <CAMqTPq=f2fQ8tnUu3UxrvfogiDCn+04HWFX8fpZkDoeYQ7ktTQ@mail.gmail.com>
User-Agent: Mutt/1.5.23 (2014-03-12)
Precedence: bulk

On Mon, Sep 24, 2018 at 05:59:12PM -0700, Vladimir Ryabtsev wrote:
> > I *suspect* VACUUM FULL won't help, since (AIUI) it copies all "visible"
...
> I am going copy the slow range into a table nearby and see if it reproduces
> (I hope "INSERT INTO t2 SELECT * FROM t1 WHERE ..." will keep existing
> order of rows). Then I could try the same after CLUSTER.

If it does an index scan, I think that will badly fail to keep the same order
of heap TIDs - it'll be inserting rows in ID order rather than in (I guess)
reverse ID order.

Justin