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Re: Hot Standby: too many KnownAssignedXids

From: Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>
To: Simon Riggs <simon(at)2ndQuadrant(dot)com>
Cc: Joachim Wieland <joe(at)mcknight(dot)de>, Fujii Masao <masao(dot)fujii(at)gmail(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Hot Standby: too many KnownAssignedXids
Date: 2010-12-02 10:41:39
Message-ID: 4CF777E3.2090701@enterprisedb.com (view raw or flat)
Thread:
Lists: pgsql-hackers
On 02.12.2010 11:02, Simon Riggs wrote:
> The cause of the issue is that replay starts at one LSN and there is a
> delay until the RunningXacts WAL record occurs. If there was no delay,
> there would be no issue at all. In CreateCheckpoint() we start by
> grabbing the WAInsertLock and later recording that pointer as part of
> the checkpoint record. My proposal is to replace the "grab the lock"
> code with the insert of the RunningXacts WAL record (when wal_level
> set), so that recovery always starts with that record type.

Oh, interesting idea. But AFAICS closing the gap between acquiring the 
running-xacts snapshot and writing it to the log is sufficient, I don't 
see what moving the running-xacts record buys us. Does it allow some 
further simplifications somewhere?

-- 
   Heikki Linnakangas
   EnterpriseDB   http://www.enterprisedb.com

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