[infinispan-dev] Hash functions

[Galder Zamarreno]

Manik,

If String's are dealt with by calling String.getBytes() which in turns  
gets processed as a byte[], why is there such a big difference  
SuperFastHash String speed and MurmurHash2 String speed (162 ms vs 56 ms)  
but there's hardly any difference between the byte[] tests (29ms vs 40ms) ?

Cheers,

On Tue, 23 Mar 2010 18:44:11 +0100, Manik Surtani <manik at jboss.org> wrote:

> 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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-- 
Galder Zamarreño
Sr. Software Engineer
Infinispan, JBoss Cache