Re: Hash Indexes

From: Andres Freund <andres(at)anarazel(dot)de>
To: Peter Geoghegan <pg(at)heroku(dot)com>
Cc: Robert Haas <robertmhaas(at)gmail(dot)com>, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, Jeff Janes <jeff(dot)janes(at)gmail(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>, Jesper Pedersen <jesper(dot)pedersen(at)redhat(dot)com>, Mithun Cy <mithun(dot)cy(at)enterprisedb(dot)com>
Subject: Re: Hash Indexes
Date: 2016-09-30 17:17:33
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On 2016-09-30 17:39:04 +0100, Peter Geoghegan wrote:
> On Fri, Sep 30, 2016 at 4:46 PM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> > I would just be very disappointed if, after the amount of work that
> > Amit and others have put into this project, the code gets rejected
> > because somebody thinks a different project would have been more worth
> > doing.
> I wouldn't presume to tell anyone else how to spend their time, and am
> not concerned about this making the hash index code any less useful
> from the user's perspective.

Me neither.

I'm concerned that this is a heck of a lot of work, and I don't think
we've reached the end of it by a good bit. I think it would have, and
probably still is, a more efficient use of time to go for the
hash-via-btree method, and rip out the current hash indexes. But that's
just me.

I find it more than a bit odd to be accused of trying to waste others
time by saying this, and that this is too late because time has already
been invested. Especially the latter never has been a standard in the
community, and while excruciatingly painful when one is the person(s)
having invested the time, it probably shouldn't be.

> > The fact that we have hash indexes already and cannot remove them
> > because too much other code depends on hash opclasses is also, in my
> > opinion, a sufficiently good reason to pursue improving them.
> I think that Andres was suggesting that hash index opclasses would be
> usable with hash-over-btree, so you might still not end up with the
> wart of having hash opclasses without hash indexes (an idea that has
> been proposed and rejected at least once before now). Andres?

Yes, that was what I was pretty much thinking. I was kind of guessing
that this might be easiest implemented as a separate AM ("hash2" ;))
that's just a layer ontop of nbtree.


Andres Freund

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