| 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 |
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| Lists: | pgsql-announce pgsql-hackers pgsql-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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