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From: Gregory Stark <[email protected]>
To: Heikki Linnakangas <[email protected]>
Cc: Juho Saarikko <[email protected]>
Cc: [email protected]
Subject: Re: BUG #3965: UNIQUE constraint fails on long column values
Date: Wed, 20 Feb 2008 09:26:35 +0000
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
References: <[email protected]>
	<[email protected]>

"Heikki Linnakangas" <[email protected]> writes:

> As others have pointed out, CREATE UNIQUE INDEX i ON ((md5(column)) is a pretty
> good work-around.

Unless you need cryptographic security I would not suggest using MD5. MD5 is
intentionally designed to take a substantial amount of CPU resources to
calculate.

Postgres's internal hash method is exposed for most data types as hashtext()
hashfloat8(), hashint4(), etc. These functions were chosen for their
lightweight design.

Cryptographic security is important only if you're concerned with people being
able to intentionally create collisions. In this scenario that's probably not
a top threat. Conceivably someone could create a denial-of-service attack
slowing down your server by causing your indexes to become unbalanced. But it
would be fairly challenging to engineer.

-- 
  Gregory Stark
  EnterpriseDB          http://www.enterprisedb.com
  Ask me about EnterpriseDB's RemoteDBA services!

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