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Message-ID: <427FFCD3.1010803@samurai.com>
Date: Tue, 10 May 2005 10:14:11 +1000
From: Neil Conway <neilc@samurai.com>
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To: "Jim C. Nasby" <decibel@decibel.org>
Cc: Christopher Petrilli <petrilli@gmail.com>,
	Ying Lu <ying_lu@cs.concordia.ca>, pgsql-general@postgresql.org,
	pgsql-performance@postgresql.org
Subject: Re: [PERFORM] "Hash index" vs. "b-tree index" (PostgreSQL
References: <427F6853.90308@cs.concordia.ca> <427F757A.8000407@samurai.com>
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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