[infinispan-dev] Consistent hashes and Hot Rod

[Dennis Reed]

Have you done a prototype and tested it to see if it improves performance?

"Inefficient" is a relative term.  The difference in .3 billionths of a 
second and .6 billionths of a second (rough numbers from a quick test)
is huge percentage wise, but only makes a difference in a tight loop 
around that operation.  if there are other operations taking a million times
as long (such as the network calls it's making after it uses the hash), 
I suspect you won't be able to measure a difference.

-Dennis

On 08/29/2013 07:35 AM, Manik Surtani wrote:
> The Hot Rod protocol current passes the size of the hash space used to clients, so that clients are able to create a consistent hash and perform smart routing.
>
> https://docs.jboss.org/author/display/ISPN/Hot+Rod+Protocol+-+Version+1.0#HotRodProtocol-Version1.0-HashDistributionAwareClientTopologyChangeHeader
> https://docs.jboss.org/author/display/ISPN/Hot+Rod+Protocol+-+Version+1.2#HotRodProtocol-Version1.2-HashDistributionAwareClientTopologyChangeHeader
>
> However there are no rules as to what this hash space is, and this forces clients to use the remainder operation when performing modular arithmetic.  This has been proven to be inefficient [1] [2] [3], and can be greatly improved if we made a simple assumption that the hash space will always be a power of two.
>
> Perhaps something we can add in v1.3 of the protocol, so that clients talking to a server using Hot Rod 1.3 can make the assumption that the hash space is a power of 2?
>
> WDYT?
>
> - Manik
>
>
> [1] http://dhruba.name/2011/07/12/performance-pattern-modulo-and-powers-of-two/
> [2] http://scicomp.stackexchange.com/questions/187/why-is-division-so-much-more-complex-than-other-arithmetic-operations
> [3] http://disruptor.googlecode.com/files/Disruptor-1.0.pdf (Page 5, last paragraph)
>
>
>
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