On 2016-09-21 19:49:15 +0300, Oskari Saarenmaa wrote:
> 21.09.2016, 15:29, Robert Haas kirjoitti:
> > For PostgreSQL, I expect the benefits of improving hash indexes to be
> > (1) slightly better raw performance for equality comparisons and (2)
> > better concurrency.
>
> There's a third benefit: with large columns a hash index is a lot smaller on
> disk than a btree index. This is the biggest reason I've seen people want
> to use hash indexes instead of btrees. hashtext() btrees are a workaround,
> but they require all queries to be adjusted which is a pain.
Sure. But that can be addressed, with a lot less effort than fixing and
maintaining the hash indexes, by adding the ability to do that
transparently using btree indexes + a recheck internally. How that
compares efficiency-wise is unclear as of now. But I do think it's
something we should measure before committing the new code.
Andres