[infinispan-dev] Generated keys affected by rehash Was: https://issues.jboss.org/browse/ISPN-977

[Dan Berindei]

On Fri, May 13, 2011 at 6:38 PM, Erik Salter <esalter at bnivideo.com> wrote:
> Yes, collocation of all keys is a large concern of my application(s).
>
> Currently, I can handle keys I'm in control of (like database-generated keys), where I can play around with the hash code.   What I would love to do is collocate that data with keys I can't control (like UUIDs) so that all cache operations can be done in the same transaction on the data owner's node.
>

By playing around with the hash code do you mean you set the hashcode
for all the keys you want on a certain server to the same value? I
imagine that would degrade performance quite a bit, because we have
HashMaps everywhere and your keys will always end up in the same hash
bucket.

ISPN-312 seems to me like a much better fit for your use case than the
KeyAffinityService. Even if you added a listener to change your keys
when the topology changes, that would mean on a rehash the keys could
get moved to the new server and then back to the old server, whereas
with ISPN-312 they will either all stay on the old node or they will
all move to the new node.

Cheers
Dan


> Erik
>
> -----Original Message-----
> From: infinispan-dev-bounces at lists.jboss.org [mailto:infinispan-dev-bounces at lists.jboss.org] On Behalf Of Manik Surtani
> Sent: Friday, May 13, 2011 5:25 AM
> To: infinispan -Dev List
> Subject: [infinispan-dev] Generated keys affected by rehash Was: https://issues.jboss.org/browse/ISPN-977
>
>
> On 11 May 2011, at 18:47, Erik Salter wrote:
>
>> Wouldn't any rehash affect the locality of these generated keys, or am I missing something?
>
> It would.  And hence ISPN-977, to address that.  Or is your concern keys already generated before the rehash?  The latter would certainly be a problem.  Perhaps, if this was important to the application, on detecting a change in topology, re-generate keys and move data around?  For other apps, move the "session" to the appropriate node?
>
> Cheers
> Manik
> --
> Manik Surtani
> manik at jboss.org
> twitter.com/maniksurtani
>
> Lead, Infinispan
> http://www.infinispan.org
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