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

Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> writes:

> > What if the hash index stored *only* the hash code? That could be useful for
> > indexing large datatypes that would otherwise create large indexes.
>
> Hmm, that could be a thought.

Hm, if you go this route of having hash indexes store tuples ordered by hash
code and storing the hash code in the index, then it seems hash indexes become
just a macro for a btree index of HASH(index columns).

I'm not saying that to criticize this plan. In fact I think that captures most
(though not all) of what a hash index should be.

It would be pretty useful. In fact if it isn't how hash indexes are
implemented then it might be useful to provide a user visible hash(ROW)
function that allows creating such indexes as functional indexes. Though
hiding it would make the SQL simpler.

--
greg