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Re: Re: [COMMITTERS] pgsql: Augment WAL records for btree delete with GetOldestXmin() to

From: Simon Riggs <simon(at)2ndQuadrant(dot)com>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Stefan Kaltenbrunner <stefan(at)kaltenbrunner(dot)cc>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: Re: [COMMITTERS] pgsql: Augment WAL records for btree delete with GetOldestXmin() to
Date: 2010-01-31 21:04:29
Message-ID: 1264971869.13782.8736.camel@ebony (view raw or flat)
Thread:
Lists: pgsql-committerspgsql-hackers
On Sun, 2010-01-31 at 15:41 -0500, Tom Lane wrote:
> Simon Riggs <simon(at)2ndQuadrant(dot)com> writes:
> > At the moment a btree delete record will cancel every request
> > 1. no matter how long they have been running
> > 2. no matter if they haven't accessed the index being cleaned (they
> > might later, is the thinking...)
> 
> That seems seriously horrid.  What is the rationale for #2 in
> particular?  I would hope that at worst this would affect sessions
> that are actively competing for the index being cleaned.

That is exactly the feedback I received from many other people and why I
prioritised the relation-specific conflict patch.

It's worse that that because point 2 effects WAL cleanup records for the
heap also.

The rationale is that a session *might* in the future access a table,
and if it did so it would receive the wrong answer *potentially*. This
is the issue I have been discussing for a long time now, in various
forms, starting on-list in Aug 2008.

-- 
 Simon Riggs           www.2ndQuadrant.com


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