Re: MultiXacts & WAL

From: "Zeugswetter Andreas DCP SD" <ZeugswetterA(at)spardat(dot)at>
To: "Josh Berkus" <josh(at)agliodbs(dot)com>, <pgsql-hackers(at)postgresql(dot)org>
Cc: "paolo romano" <paolo(dot)romano(at)yahoo(dot)it>, "Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us>, "Heikki Linnakangas" <hlinnaka(at)iki(dot)fi>
Subject: Re: MultiXacts & WAL
Date: 2006-06-19 08:39:50
Message-ID: E1539E0ED7043848906A8FF995BDA5790116C079@m0143.s-mxs.net
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> I would like to see some checking of this, though. Currently
> I'm doing testing of PostgreSQL under very large numbers of
> connections (2000+) and am finding that there's a huge volume
> of xlog output ... far more than
> comparable RDBMSes. So I think we are logging stuff we
> don't really have to.

I think you really have to lengthen the checkpoint interval to reduce
WAL overhead (20 min or so). Also imho you cannot only compare the log
size/activity since other db's write part of what pg writes to WAL to
other areas (physical log, rollback segment, ...).

If we cannot afford lenghtening the checkpoint interval because of
too heavy checkpoint load, we need to find ways to tune bgwriter, and
not
reduce checkpoint interval.

Andreas

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