Gregory Stark wrote:
"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.
Return type of hash* functions is just 32 bits. I wonder if that's wide
enough to avoid accidental collisions? Depends on the application of
course...
--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com
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