| From: | "Heikki Linnakangas" <heikki(at)enterprisedb(dot)com> |
|---|---|
| To: | "Gregory Stark" <stark(at)enterprisedb(dot)com> |
| Cc: | "Simon Riggs" <simon(at)2ndquadrant(dot)com>, "Dann Corbit" <DCorbit(at)connx(dot)com>, "Jonah H(dot) Harris" <jonah(dot)harris(at)gmail(dot)com>, "Xiao Meng" <mx(dot)cogito(at)gmail(dot)com>, <pgsql-hackers(at)postgresql(dot)org>, "Kenneth Marshall" <ktm(at)rice(dot)edu> |
| Subject: | Re: [PATCH]-hash index improving |
| Date: | 2008-07-18 14:44:13 |
| Message-ID: | 4880AC3D.5050704@enterprisedb.com |
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| Lists: | pgsql-hackers |
Gregory Stark wrote:
> For i/o-bound databases with very large indexes there should be an opportunity
> where btree lookups are O(logn) and hash lookups can in theory be O(1).
Ignoring the big-O complexity, if a hash index only stores a 32-bit hash
code instead of the whole key, it could be a big win in storage size,
and therefore in cache-efficiency and performance, when the keys are
very long.
Granted, it's not very common to use a 1K text field as a key column...
--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com
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