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Re: Bug: Unreferenced temp tables disables vacuum to update xid

From: Gregory Stark <stark(at)enterprisedb(dot)com>
To: "Joshua D(dot) Drake" <jd(at)commandprompt(dot)com>
Cc: "Bruce Momjian" <bruce(at)momjian(dot)us>, "Alvaro Herrera" <alvherre(at)commandprompt(dot)com>, <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Bug: Unreferenced temp tables disables vacuum to update xid
Date: 2008-01-07 18:28:49
Message-ID: 87myrh4hi6.fsf@oxford.xeocode.com (view raw or flat)
Thread:
Lists: pgsql-hackers
"Joshua D. Drake" <jd(at)commandprompt(dot)com> writes:

> On Mon, 7 Jan 2008 11:58:29 -0500 (EST)
> Bruce Momjian <bruce(at)momjian(dot)us> wrote:
>
>> I assume it is this TODO item:
>> 
>>         o Prevent long-lived temporary tables from causing frozen-xid
>>           advancement starvation
>> 
>>           The problem is that autovacuum cannot vacuum them to set
>> frozen xids; only the session that created them can do that.
>>           http://archives.postgresql.org/pgsql-general/2007-06/msg01645.php
>> 
>> but am confused how the fix worked.  Have all of these backends been
>> active for 1 billion transactions?
>
> Well it certainly appears that the TODO item is related. However there
> are a couple of differences.

Yeah, it seems there are two bugs here. 1) temporary tables prevent frozen-xid
advancement and 2) if a process dies at the wrong moment it's possible to
temporary tables. Either one alone is pretty minor but I guess the combination
is lethal.

-- 
  Gregory Stark
  EnterpriseDB          http://www.enterprisedb.com
  Ask me about EnterpriseDB's PostGIS support!

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