[infinispan-dev] Hash functions

[Manik Surtani]

On 29 Mar 2010, at 10:30, Galder Zamarreno wrote:

> 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) ?

No idea.  Microbenchmarks are notoriously fickle though, I will try and run this again over a larger sample size to smooth things out a bit.

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