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Re: What's the XID?

From: Jeff Frost <jeff(at)frostconsultingllc(dot)com>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Andrew Sullivan <ajs(at)crankycanuck(dot)ca>, pgsql-admin(at)postgresql(dot)org
Subject: Re: What's the XID?
Date: 2007-12-27 16:27:16
Message-ID: Pine.LNX.4.64.0712270823430.2757@glacier.frostconsultingllc.com (view raw or flat)
Thread:
Lists: pgsql-admin
On Thu, 27 Dec 2007, Tom Lane wrote:

> Andrew Sullivan <ajs(at)crankycanuck(dot)ca> writes:
>> On Wed, Dec 26, 2007 at 05:48:14PM -0800, ivan.hou wrote:
>>> if i executed "select * from mydb" twice, the XID wil be increased by 2
>
>> Yep.  Whereas if you did
>
>> 	BEGIN;
>> 	SELECT 1;
>> 	SELECT 1;
>> 	COMMIT;
>
>> the xid would be increased by 1.
>
> But note that as of 8.3, SELECT-only transactions won't acquire an
> XID and hence won't advance the counter.  So if you're thinking of
> writing code that depends on that behavior, don't.

>
Tom,

So, the new XID counter won't advance unless there's at least one 
INSERT/UPDATE/DELETE in the transaction?  Does it also update for SELECTs that 
call a function which does some write activity?

Is there a new counter (or old one that I don't know about) that keeps track 
of the SELECT-only transactions?


-- 
Jeff Frost, Owner 	<jeff(at)frostconsultingllc(dot)com>
Frost Consulting, LLC 	http://www.frostconsultingllc.com/
Phone: 650-780-7908	FAX: 650-649-1954

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