From: Jim C. Nasby <decibel@decibel.org>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Neil Conway <neilc@samurai.com>
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 10:39:27 -0500
Message-ID: <20050510153927.GB31103@decibel.org> (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>
On Tue, May 10, 2005 at 12:10:57AM -0400, Tom Lane wrote:
> be responsive to your search.) (This also brings up the thought that
> it might be interesting to support hash buckets smaller than a page ...
> but I don't know how to make that work in an adaptive fashion.)
IIRC, other databases that support hash indexes also allow you to define
the bucket size, so it might be a good start to allow for that. DBA's
usually have a pretty good idea of what a table will look like in
production, so if there's clear documentation on the effect of bucket
size a good DBA should be able to make a good decision.
What's the challange to making it adaptive, comming up with an algorithm
that gives you the optimal bucket size (which I would think there's
research on...) or allowing the index to accommodate different bucket
sizes existing in the index at once? (Presumably you don't want to
re-write the entire index every time it looks like a different bucket
size would help.)
--
Jim C. Nasby, Database Consultant decibel@decibel.org
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To: pgsql-performance@postgresql.org
Cc: decibel@decibel.org, tgl@sss.pgh.pa.us, neilc@samurai.com, 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: <20050510153927.GB31103@decibel.org>
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