From: Neil Conway <neilc@samurai.com>
To: 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 10:14:11 +1000
Message-ID: <427FFCD3.1010803@samurai.com> (raw)
In-Reply-To: <20050509165133.GJ35026@decibel.org>
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>
Jim C. Nasby wrote:
>> No, hash joins and hash indexes are unrelated.
> I know they are now, but does that have to be the case?
I mean, the algorithms are fundamentally unrelated. They share a bit of
code such as the hash functions themselves, but they are really solving
two different problems (disk based indexing with (hopefully) good
concurrency and WAL logging vs. in-memory joins via hashing with spill
to disk if needed).
> Like I said, I don't know the history, so I don't know why we even
> have them to begin with.
As I said, the idea of using hash indexes for better performance on
equality scans is perfectly valid, it is just the implementation that
needs work.
-Neil
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To: pgsql-performance@postgresql.org
Cc: 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: <427FFCD3.1010803@samurai.com>
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