From: Neil Conway <neilc@samurai.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
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: Tue, 10 May 2005 14:25:06 +1000
Message-ID: <428037A2.4060304@samurai.com> (raw)
In-Reply-To: <4407.1115698257@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>
Tom Lane wrote:
> On the other hand, once you reach the target index page, a hash index
> has no better method than linear scan through all the page's index
> entries to find the actually wanted key(s)
I wonder if it would be possible to store the keys in a hash bucket in
sorted order, provided that the necessary ordering is defined for the
index keys -- considering the ubiquity of b+-trees in Postgres, the
chances of an ordering being defined are pretty good. Handling overflow
pages would be tricky: perhaps we could store the entries in a given
page in sorted order, but not try to maintain that order for the hash
bucket as a whole. This would mean we'd need to do a binary search for
each page of the bucket, but that would still be a win.
-Neil
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To: pgsql-performance@postgresql.org
Cc: neilc@samurai.com, tgl@sss.pgh.pa.us, 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: <428037A2.4060304@samurai.com>
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