From: | AP <ap(at)zip(dot)com(dot)au> |
---|---|
To: | Mark Kirkwood <mark(dot)kirkwood(at)catalyst(dot)net(dot)nz> |
Cc: | Andres Freund <andres(at)anarazel(dot)de>, Jeff Janes <jeff(dot)janes(at)gmail(dot)com>, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: Hash Indexes |
Date: | 2016-09-19 09:46:11 |
Message-ID: | 20160919094611.GS14430@zip.com.au |
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Lists: | pgsql-hackers |
On Mon, Sep 19, 2016 at 05:50:13PM +1200, Mark Kirkwood wrote:
> >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.
>
> While I see the point of what you are saying here, I recall all previous
> discussions about has indexes tended to go a bit like this:
>
> - until WAL logging of hash indexes is written it is not worthwhile trying
> to make improvements to them
> - WAL logging will be a lot of work, patches 1st please
>
> Now someone has done that work, and we seem to be objecting that because
> they are not improved then the patches are (maybe) not worthwhile. I think
> that is - essentially - somewhat unfair.
My understanding of hash indexes is that they'd be good for indexing
random(esque) data (such as UUIDs or, well, hashes like shaX). If so
then I've got a DB that'll be rather big that is the very embodiment
of such a use case. It indexes such data for equality comparisons
and runs on SELECT, INSERT and, eventually, DELETE.
Lack of WAL and that big warning in the docs is why I haven't used it.
Given the above, many lamentations from me that it wont be available
for 9.6. :( When 10.0 comes I'd probably go to the bother of re-indexing
with hash indexes.
Andrew
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