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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: "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 19:27:11
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-patches
On Fri, 2007-03-23 at 17:35 -0400, Tom Lane wrote:
> To make intra-transaction advancing of xmin possible, we'd need to
> explicitly track all of the backend's live snapshots, probably by
> introducing a "snapshot cache" manager that gives out tracked
> refcounts
> as we do for some other structures like catcache entries.  This might
> have some other advantages (I think most of the current CopySnapshot
> operations could be replaced by refcount increments) 

Seems like we should do this for many reasons, whether or not this is
one of them. I seem to have butted heads and lost more than once with
not being able to tell which Snapshots exist.

  Simon Riggs             

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