Re: SSI patch version 14

From: Dan Ports <drkp(at)csail(dot)mit(dot)edu>
To: Kevin Grittner <Kevin(dot)Grittner(at)wicourts(dot)gov>
Cc: heikki(dot)linnakangas(at)enterprisedb(dot)com, simon(at)2ndQuadrant(dot)com, markus(at)bluegap(dot)ch, pgsql-hackers(at)postgresql(dot)org
Subject: Re: SSI patch version 14
Date: 2011-02-08 18:34:46
Message-ID: 20110208183446.GX9421@csail.mit.edu
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On Tue, Feb 08, 2011 at 10:14:44AM -0600, Kevin Grittner wrote:
> I do have some concern that if this defaults to too low a number,
> those who try SSI without bumping it and restarting the postmaster
> will not like the performance under load very much. SSI performance
> would not be affected by a low setting under light load when there
> isn't a long-running READ WRITE transaction.

If we're worried about this, we could add a log message the first time
SummarizeOldestCommittedXact is called, to suggest increasing the GUC
for number of SerializableXacts. This also has the potential benefit of
alerting the user that there's a long-running transaction, in case that's
unexpected (say, if it were caused by a wedged client)

I don't have any particular opinion on what the default value of the
GUC should be.

Dan

--
Dan R. K. Ports MIT CSAIL http://drkp.net/

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