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Message-ID: <4678E6F5.6040300@enterprisedb.com>
Date: Wed, 20 Jun 2007 09:36:05 +0100
From: Heikki Linnakangas <heikki@enterprisedb.com>
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To: PFC <lists@peufeu.com>
CC: pgsql-performance@postgresql.org
Subject: Re: Short row header
References: <op.tt7mw6dccigqcu@apollo13>
In-Reply-To: <op.tt7mw6dccigqcu@apollo13>
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PFC wrote:
> 
>     I have this "poll results" table with just 3 integer fields, which 
> is never updated, only inserted/deleted...
>     Did the Devs consider an option to have VACUUM reduce the row header 
> sizes for tuples that are long commited and are currently visible to all 
> transactions ?

That has been suggested before, but IIRC it wasn't considered to be 
worth it. It would only save 4 bytes (the xmin field) per tuple, the 
free space would be scattered around all pages making it less useful, 
and having to deal with two different header formats would make 
accessing the header fields more complex.

> (even if this makes the tuples non-updateable, as long as 
> they can be deleted, it would be OK for this type of tables).

That would save another 6 bytes per tuple (ctid field), but we generally 
stay away from things that impose limitations like that.

-- 
   Heikki Linnakangas
   EnterpriseDB   http://www.enterprisedb.com