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Re: [PATCHES] pg_freespacemap question

From: Mark Kirkwood <markir(at)paradise(dot)net(dot)nz>
To: Christopher Kings-Lynne <chriskl(at)familyhealth(dot)com(dot)au>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Tatsuo Ishii <ishii(at)sraoss(dot)co(dot)jp>, alvherre(at)commandprompt(dot)com, peter_e(at)gmx(dot)net, pgsql-hackers(at)postgresql(dot)org, pgsql-patches(at)postgresql(dot)org
Subject: Re: [PATCHES] pg_freespacemap question
Date: 2006-03-13 04:37:00
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Lists: pgsql-hackerspgsql-patches
Christopher Kings-Lynne wrote:
>> The point here is that if tuples require 50 bytes, and there are 20
>> bytes free on a page, pgstattuple counts 20 free bytes while FSM
>> ignores the page.  Recording that space in the FSM will not improve
>> matters, it'll just risk pushing out FSM records for pages that do
>> have useful amounts of free space.
> Maybe an overloaded pgstattuple function that allows you to request FSM 
> behavior?

That's a nice idea - could also do equivalently by adding an extra 
column "usable_free_space" or some such, and calculating this using FSM 



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