From: | Andres Freund <andres(at)anarazel(dot)de> |
---|---|
To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | Oskari Saarenmaa <os(at)ohmu(dot)fi>, Robert Haas <robertmhaas(at)gmail(dot)com>, Bruce Momjian <bruce(at)momjian(dot)us>, 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: | 2016-09-22 02:33:58 |
Message-ID: | 20160922023358.gc6r3glojskijcxw@alap3.anarazel.de |
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Lists: | pgsql-hackers |
On 2016-09-21 22:23:27 -0400, Tom Lane wrote:
> Andres Freund <andres(at)anarazel(dot)de> writes:
> > 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.
>
> TBH, I think we should reject that argument out of hand. If someone
> wants to spend time developing a hash-wrapper-around-btree AM, they're
> welcome to do so. But to kick the hash AM as such to the curb is to say
> "sorry, there will never be O(1) index lookups in Postgres".
Note that I'm explicitly *not* saying that. I just would like to see
actual comparisons being made before investing significant amounts of
code and related effort being invested in fixing the current hash table
implementation. And I haven't seen a lot of that. If the result of that
comparison is that hash-indexes actually perform very well: Great!
> always be superior, I don't see how it follows that we should refuse to
> commit work that's already been done. Is committing it somehow going to
> prevent work on the btree-wrapper approach?
The necessary work seems a good bit from finished.
Greetings,
Andres Freund
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