Re: Why could different data in a table be processed with different performance?

From: Justin Pryzby <pryzby(at)telsasoft(dot)com>
To: Vladimir Ryabtsev <greatvovan(at)gmail(dot)com>
Cc: f(dot)pardi(at)portavita(dot)eu, pgsql-performance(at)lists(dot)postgresql(dot)org
Subject: Re: Why could different data in a table be processed with different performance?
Date: 2018-09-25 02:19:54
Message-ID: 20180925021954.GW2471@telsasoft.com
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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

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