[Building Sakai] Clustering a HashMap

[Adrian Fish]

Thanks for the replies Ian and Lance. From the ehCache docs I gained the 
impression that the replication was more fine grained than you describe. 
What you are saying, if I understand correctly, is that entire strata 
within the main map that ehcache uses are replaced if even one element 
at that level is changed. That's obviously a bit heavy, so I'll think again.

I'll have a look at the tools you've suggested, thanks !

Cheers,

Adrian.

On 17/01/2011 18:00, Ian Boston wrote:
> On 14 Jan 2011, at 12:45, Adrian Fish wrote:
>
>> At the moment I'm playing with creating an EhCacheFactory bean in my
>> spring config, using the MemoryService to create a Cache instance and
>> then putting the hashmaps in that if they are not already there.
> IIRC ehCache replicates on element levels. So if you put a hashmap into a Cache as a single Cache element, then every time you modifiy the map it will replicate, which will soon kill your server with replication traffic.
>
> Try and put the contents of the map at the lowest level in the map, then when you change one item, only that will be replicated.
> Also think hard about if you really want replication, or just invalidation. In general relying on replication as a mechanism to distribute messages is soon going to overload a production system. I would look at things like node.js or cometD and communicate a chat end point to the each user with messages going to that destination rather than rely on a replicated, in memory structure to achieve this.
>
> If you really must use replication and ehCache, then configure it with JGroups underneath as thats probably the most efficient transport if you servers are on the same subnet,
>
> If you want an alternative, take a look at infinspan which does a better job of replication in larger clusters, and then there is memcached (but you will have to OS level things on install)
>
> HTH
> Ian
>
>
>

-- 
==================================
Adrian Fish
Software Engineer
Centre for e-Science
Bowland Tower South C Floor
Lancaster University
Lancaster
LA1 4YW
email: a.fish at lancaster.ac.uk

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