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