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Re: Much Ado About COUNT(*)

From: Christopher Kings-Lynne <chriskl(at)familyhealth(dot)com(dot)au>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: "Jonah H(dot) Harris" <jharris(at)tvi(dot)edu>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: Much Ado About COUNT(*)
Date: 2005-01-13 10:12:49
Message-ID: 41E649A1.3030009@familyhealth.com.au (view raw or flat)
Thread:
Lists: pgsql-announcepgsql-hackerspgsql-patches
> The fundamental problem is that you can't do it without adding at least
> 16 bytes, probably 20, to the size of an index tuple header.  That would
> double the physical size of an index on a simple column (eg an integer
> or timestamp).  The extra I/O costs and extra maintenance costs are
> unattractive to say the least.  And it takes away some of the
> justification for the whole thing, which is that reading an index is
> much cheaper than reading the main table.  That's only true if the index
> is much smaller than the main table ...

Well, the trick would be to have it specified per-index, then it's up to 
the user whether it's faster or not...

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