Re: [GENERAL] "Hash index" vs. "b-tree index" (PostgreSQL

"Jim C. Nasby" <decibel@decibel.org> writes:
> What's the challange to making it adaptive, comming up with an algorithm
> that gives you the optimal bucket size (which I would think there's
> research on...) or allowing the index to accommodate different bucket
> sizes existing in the index at once? (Presumably you don't want to
> re-write the entire index every time it looks like a different bucket
> size would help.)

Exactly.  That's (a) expensive and (b) really hard to fit into the WAL
paradigm --- I think we could only handle it as a REINDEX.  So if it
were adaptive at all I think we'd have to support multiple bucket sizes
existing simultaneously in the index, and I do not see a good way to do
that.

Allowing a bucket size to be specified at CREATE INDEX doesn't seem out
of line though.  We'd have to think up a scheme for index-AM-specific
index parameters ...

            regards, tom lane