> >By the way, I didn't find many comments about the pros and
> >cons of btree/hash indexes in the docs, nor in Bruce's book...
>
> If I remember my data-structures (from way back when) correctly then:
>
> hash indexes are only good for very fast single row lookups.
>
> isam indexes are good for range lookups, but the implementations that
> I've seen of isam indexes doesn't allow for dynamic index expanding.
>
> btree is good for both. btree won't be quite as fast as a hash for a
> single row lookup, but still very fast. btree won't (if I remember
> correctly) be quite as fast as an isam for a range lookup, but still
> very fast. Also, btree allows for dynamic index expansion.
Sorry to be replying to late.
First, I did not mention btree vs. hash in my book because we have not
seen any empirical evidence that hash is faster than btree in
PostgreSQL. Also, I wanted simplicity, so I did not get into the issue.
As far as ISAM, yes, I do miss its absense. The best we have now is
btree combined with the CLUSTER command. Since ISAM is not
self-optimizing, having to run CLUSTER on a btree is similar to having
to recreate the ISAM every so often. Not sure what gain we would get by
having a native ISAM vs our current btree/CLUSTER capability.
--
Bruce Momjian | http://candle.pha.pa.us
pgman@candle.pha.pa.us | (610) 853-3000
+ If your life is a hard drive, | 830 Blythe Avenue
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