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To: Jean-Luc Lachance <jllachan@nsd.ca>
Cc: pgsql-sql@postgresql.org, pgsql-general@postgresql.org
Subject: Re: Getting acces to MVCC version number 
In-reply-to: <3D8B676D.3109ACFA@nsd.ca> 
References: <200209201619.g8KGJ4J00624@candle.pha.pa.us>
	<3D8B676D.3109ACFA@nsd.ca>
Comments: In-reply-to Jean-Luc Lachance <jllachan@nsd.ca>
	message dated "Fri, 20 Sep 2002 14:22:37 -0400"
Date: Fri, 20 Sep 2002 17:23:32 -0400
Message-ID: <2566.1032557012@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
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Jean-Luc Lachance <jllachan@nsd.ca> writes:
> How about making available the MVCC last version number just like oid is
> available.  This would simplify a lot of table design.  You know, having
> to add a field "updated::timestamp" to detect when a record was updated
> while viewing it (a la pgaccess).
> That way, if the version number do not match, one would know that the
> reccord was updated since last retrieved.

> What do think?

I think it's already there: see xmin and cmin.  Depending on your needs,
testing xmin might be enough (you'd only need to pay attention to cmin
if you wanted to notice changes within your own transaction).

			regards, tom lane