From: Greg Stark <gsstark@mit.edu>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Greg Stark <gsstark@mit.edu>
Cc: Neil Conway <neilc@samurai.com>
Cc: Jim C. Nasby <decibel@decibel.org>
Cc: Christopher Petrilli <petrilli@gmail.com>
Cc: Ying Lu <ying_lu@cs.concordia.ca>
Cc: pgsql-general@postgresql.org
Cc: pgsql-performance@postgresql.org
Subject: Re: [PERFORM] "Hash index" vs. "b-tree index" (PostgreSQL
Date: 10 May 2005 13:35:59 -0400
Message-ID: <87wtq7q8zk.fsf@stark.xeocode.com> (raw)
In-Reply-To: <9871.1115733198@sss.pgh.pa.us>
References: <427F6853.90308@cs.concordia.ca>
<427F757A.8000407@samurai.com>
<59d991c405050908271b55e673@mail.gmail.com>
<427F8321.5030702@samurai.com>
<20050509163423.GH35026@decibel.org>
<427F9211.2090008@samurai.com>
<20050509165133.GJ35026@decibel.org>
<427FFCD3.1010803@samurai.com>
<4407.1115698257@sss.pgh.pa.us>
<428037A2.4060304@samurai.com>
<6686.1115700888@sss.pgh.pa.us>
<878y2nsj7i.fsf@stark.xeocode.com>
<9871.1115733198@sss.pgh.pa.us>
Tom Lane <tgl@sss.pgh.pa.us> writes:
> > What if the hash index stored *only* the hash code? That could be useful for
> > indexing large datatypes that would otherwise create large indexes.
>
> Hmm, that could be a thought.
Hm, if you go this route of having hash indexes store tuples ordered by hash
code and storing the hash code in the index, then it seems hash indexes become
just a macro for a btree index of HASH(index columns).
I'm not saying that to criticize this plan. In fact I think that captures most
(though not all) of what a hash index should be.
It would be pretty useful. In fact if it isn't how hash indexes are
implemented then it might be useful to provide a user visible hash(ROW)
function that allows creating such indexes as functional indexes. Though
hiding it would make the SQL simpler.
--
greg
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To: pgsql-performance@postgresql.org
Cc: gsstark@mit.edu, tgl@sss.pgh.pa.us, neilc@samurai.com, decibel@decibel.org, petrilli@gmail.com, ying_lu@cs.concordia.ca, pgsql-general@postgresql.org
Subject: Re: [PERFORM] "Hash index" vs. "b-tree index" (PostgreSQL
In-Reply-To: <87wtq7q8zk.fsf@stark.xeocode.com>
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