From: Tom Lane <tgl@sss.pgh.pa.us>
To: Alvaro Herrera <alvherre@2ndquadrant.com>
cc: bkrug <bkrug@usatech.com>, pgsql-performance@postgresql.org
Subject: Re: Avoiding Refreezing XIDs Repeatedly
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Comments: In-reply-to Alvaro Herrera <alvherre@2ndquadrant.com>
 message dated "Mon, 09 Feb 2015 16:10:35 -0300"
Date: Mon, 09 Feb 2015 15:00:34 -0500
Message-ID: <14441.1423512034@sss.pgh.pa.us>
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Alvaro Herrera <alvherre@2ndquadrant.com> writes:
> bkrug wrote:
>> The problem I'm facing is that I have many large (several GB) tables that are
>> not being changed (they are several days old) but auto-vacuum keeps scanning
>> and updating them every time the xid wraps around and thus my rsync back-up
>> process sees that the disk files have changed and must copy them.

> We have considered changing this, but it needs a concerted effort.  It's
> not a simple problem.

I'm not following.  Yes, the tables will be *scanned* at least once per
XID wraparound cycle, but if they are in fact static then they should not
be changing once the tuples have been frozen the first time.  If this is
incurring continuing rsync work then something else is going on.

			regards, tom lane


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