[infinispan-dev] Hash functions

[Bryan Grunow]

This may have been stated somewhere but will the Hash function be
configurable?  At least at the deployment level.  Not sure about at the
cache level.

I could see where different deployments might want different hash
attributes.  E.g. spread vs. speed or CPU neutral behavior vs. spread,
etc.

Bryan

-----Original Message-----
From: infinispan-dev-bounces at lists.jboss.org
[mailto:infinispan-dev-bounces at lists.jboss.org] On Behalf Of Manik
Surtani
Sent: Tuesday, March 23, 2010 10:44 AM
To: infinispan -Dev List
Subject: [infinispan-dev] Hash functions

Some very early results,

	http://pastie.org/883111

Only testing MurmurHash2 (endian-neutral variant which is 2x as slow as
the original algo) and SuperFastHash.  I haven't implemented FNV-1 as
yet.

Some notes:

* Test was run over 100k random keys
* Max size for a String and byte[] key set to 16.  Actual size is a
random number between 1 and MaxSize.
* Functions mainly implemented to handle byte[]'s.
* Functions handle Strings by calling String.getBytes().  The bulk of
the time spent in String keys is therefore attributed to
String.getBytes().
* Functions handle Object hashcodes by taking the int hashcode and
creating a 4-element byte[] out of it.  Again, the bulk of the time
spent here is in this conversion.
* Keys generated before any measurements taken, a full cycle run to warm
up the hotspot compiler as well.

Looks like MurmurHash2, despite using the slower version to accommodate
CPU endian neutral behaviour, is winning in terms of distribution.  And
by a fair way too.

For those interested in the test and the hash impls, have a look at this
(dependency on Apache commons-math):

	http://pastie.org/883135

Cheers
--
Manik Surtani
manik at jboss.org
Lead, Infinispan
Lead, JBoss Cache
http://www.infinispan.org
http://www.jbosscache.org





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