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Re: Improvement of procArray.xmin for VACUUM

From: "Simon Riggs" <simon(at)2ndquadrant(dot)com>
To: "Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: "Heikki Linnakangas" <heikki(at)enterprisedb(dot)com>,"Bruce Momjian" <bruce(at)momjian(dot)us>,"PostgreSQL-patches" <pgsql-patches(at)postgresql(dot)org>
Subject: Re: Improvement of procArray.xmin for VACUUM
Date: 2007-03-26 19:37:16
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-patches
On Sat, 2007-03-24 at 11:48 -0400, Tom Lane wrote:

> Also, at some point a long-running transaction becomes a bottleneck
> simply because its XID is itself the oldest thing visible in the
> ProcArray and is determining everyone's xmin.  How much daylight is
> there really between "your xmin is old" and "your xid is old"?

Hmm, yes. How often do we have an LRT that consists of multiple
statements of significant duration? Not often, I'd wager. 

How much does it cost to optimise for this case?

Did Heikki's patch to move the xmin forward during VACUUM get rejected?
That seems like it has a much wider use case.

  Simon Riggs             

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