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Re: PATCH to allow concurrent VACUUMs to not lock each

From: Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us>
To: Hannu Krosing <hannu(at)skype(dot)net>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Neil Conway <neilc(at)samurai(dot)com>, pgsql-patches(at)postgresql(dot)org
Subject: Re: PATCH to allow concurrent VACUUMs to not lock each
Date: 2006-03-21 03:34:33
Message-ID: 200603210334.k2L3YXi16741@candle.pha.pa.us (view raw or flat)
Thread:
Lists: pgsql-hackerspgsql-patches
This is going to need a significant safety review.

Your patch has been added to the PostgreSQL unapplied patches list at:

	http://momjian.postgresql.org/cgi-bin/pgpatches

It will be applied as soon as one of the PostgreSQL committers reviews
and approves it.

---------------------------------------------------------------------------


Hannu Krosing wrote:
> On K, 2005-08-17 at 15:40 -0400, Tom Lane wrote:
> >                            Saatja: 
> > Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
> >                           Kellele: 
> > Bruce Momjian
> > <pgman(at)candle(dot)pha(dot)pa(dot)us>, Hannu
> > Krosing <hannu(at)tm(dot)ee>, Neil Conway
> > <neilc(at)samurai(dot)com>, pgsql-
> > patches(at)postgresql(dot)org
> >                             Teema: 
> > Re: [PATCHES] PATCH to allow
> > concurrent VACUUMs to not lock each
> >                           Kuup?ev: 
> > Wed, 17 Aug 2005 15:40:53 -0400
> > (22:40 EEST)
> > 
> > Just for the archives, attached is as far as I'd gotten with cleaning
> > up
> > Hannu's patch before I realized that it wasn't doing what it needed to
> > do.  This fixes an end-of-transaction race condition (can't unset
> > inVacuum before xact end, unless you want OldestXmin going backwards
> > from the point of view of other people) and improves the documentation
> > of what's going on.  But unless someone can convince me that it's safe
> > to mess with GetSnapshotData, it's unlikely this'll ever get applied.
> > 
> > 
> > 
> 
> Attached is a patch, based on you last one, which messes with
> GetSnapshotData in what I think is a safe way.
> 
> It introduces another attribute to PROC , proc->nonInVacuumXmin and
> computes this in addition to prox->xmin inside GetSnapshotData.
> 
> When (and only when) GetOldestXmin is called with ignoreVacuum=true,
> then proc->nonInVacuumXmin is checked instead of prox->xmin.
> 
> I believe that this will make this change invisible to all other places
> where GetSnapshotData or GetOldestXmin is used.
> 
> -- 
> Hannu Krosing <hannu(at)skype(dot)net>
> 
> 
> 
> 
> 

[ Attachment, skipping... ]

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-- 
  Bruce Momjian   http://candle.pha.pa.us
  SRA OSS, Inc.   http://www.sraoss.com

  + If your life is a hard drive, Christ can be your backup. +

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