Re: Hash Indexes

On 2016-09-16 09:12:22 -0700, Jeff Janes wrote:
> On Thu, Sep 15, 2016 at 7:23 AM, Andres Freund  wrote:
> > One earlier question about this is whether that is actually a worthwhile
> > goal.  Are the speed and space benefits big enough in the general case?
> > Could those benefits not be achieved in a more maintainable manner by
> > adding a layer that uses a btree over hash(columns), and adds
> > appropriate rechecks after heap scans?
> >
> > Note that I'm not saying that hash indexes are not worthwhile, I'm just
> > doubtful that question has been explored sufficiently.

> I think that exploring it well requires good code.  If the code is good,
> why not commit it?

Because getting there requires a lot of effort, debugging it afterwards
would take effort, and maintaining it would also takes a fair amount?
Adding code isn't free.

I'm rather unenthused about having a hash index implementation that's
mildly better in some corner cases, but otherwise doesn't have much
benefit. That'll mean we'll have to step up our user education a lot,
and we'll have to maintain something for little benefit.

Andres