On Thu, Jul 27, 2006 at 01:46:01PM -0400, Alvaro Herrera wrote: > Jim Nasby wrote: > > On Jul 25, 2006, at 3:31 PM, Tom Lane wrote: > > >Hannu Krosing <[EMAIL PROTECTED]> writes: > > > >>What would be the use-case for hash indexes ? And what should be > > >>done to make them faster than btree ? > > > > > >If we knew, we'd do it ;-) But no one's put enough effort into it > > >to find out. > > > > Do they use the same hash algorithm as hash joins/aggregation? If so, > > wouldn't hash indexes be faster for those operations than regular > > indexes? > > The main problem doesn't seem to be in the hash algorithm (which I > understand to mean the hashing function), but in the protocol for > concurrent access of index pages, and the distribution of keys in pages > of a single hash key. > > This is described in a README file or a code comment somewhere in the > hash AM code. Someone needs to do some profiling to find out what the > bottleneck really is, and ideally find a way to fix it.
What I'm getting at is that I've never seen any explanation for the theoretical use cases where a hash index would outperform a btree. If we knew what kind of problems hash indexes were supposed to solve, we could try and interest people who are solving those kinds of problems in fixing hash indexes. -- Jim C. Nasby, Sr. Engineering Consultant [EMAIL PROTECTED] Pervasive Software http://pervasive.com work: 512-231-6117 vcard: http://jim.nasby.net/pervasive.vcf cell: 512-569-9461 ---------------------------(end of broadcast)--------------------------- TIP 1: if posting/reading through Usenet, please send an appropriate subscribe-nomail command to [EMAIL PROTECTED] so that your message can get through to the mailing list cleanly
