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Message-ID: <427F757A.8000407@samurai.com>
Date: Tue, 10 May 2005 00:36:42 +1000
From: Neil Conway <neilc@samurai.com>
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To: Ying Lu <ying_lu@cs.concordia.ca>
Cc: pgsql-general@postgresql.org, pgsql-performance@postgresql.org
Subject: Re: "Hash index" vs. "b-tree index" (PostgreSQL 8.0)
References: <427F6853.90308@cs.concordia.ca>
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Ying Lu wrote:
> May I know for simple "=" operation query, for "Hash index" vs. "B-tree" 
> index, which can provide better performance please?

I don't think we've found a case in which the hash index code 
outperforms B+-tree indexes, even for "=". The hash index code also has 
a number of additional issues: for example, it isn't WAL safe, it has 
relatively poor concurrency, and creating a hash index is significantly 
slower than creating a b+-tree index.

-Neil