Re: Write Ahead Logging for Hash Indexes

Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> It's become pretty clear to me that there are a bunch of other things
> about hash indexes which are not exactly great, the worst of which is
> the way they grow by DOUBLING IN SIZE.

Uh, what? Growth should happen one bucket-split at a time.

> Other things that are not so great:

> - no multi-column support
> - no amcanunique support
> - every insert dirties the metapage
> - splitting is generally too aggressive; very few overflow pages are
> ever created unless you have piles of duplicates

Yeah. It's a bit hard to see how to add multi-column support unless you
give up the property of allowing queries on a subset of the index columns.
Lack of amcanunique seems like mostly a round-tuit shortage. The other
two are implementation deficiencies that maybe we can remedy someday.

Another thing I'd like to see is support for 64-bit hash values.

But all of these were mainly blocked by people not wanting to sink effort
into hash indexes as long as they were unusable for production due to lack
of WAL support. So this is a huge step forward.

regards, tom lane