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From James Taylor <ja...@jamestaylor.org>
Subject Re: Hibernate and JCS Questions
Date Thu, 05 Dec 2002 02:55:54 GMT
> 1) How mature is JCS? Who is using it? On how many machines? With which of
> the three major configurations (fully distributed, client/server,
> client/cluster)?

I am using it. Two machines, memory caches on each. Put only lateral
distribution between them with javagroups. Quite basic really.

Others? (I'm curious too)

> 2) What was the process by which Gavin gained sufficient confidence in JCS
> to include it in Hibernate?
> 
> 3) Why does Gavin indicate that JCS can't be used in a clustered read-write
> environment, in contradiction to the JCS documentation?

I suspect the biggest problem is that there is no distributed locking,
for JCS, which makes it difficult to use for O/R mapping. In my case, we
cache immutable read mostly data objects, and when the underlying data
store is updated for an entity, it is purged from the cache. 

For more mutable data, I do not cache.

> 4) If we were able to commit to using Hibernate in a read-only fashion and
> doing our data writing some other way, changing the data out from under
> Hibernate, which various legacy admin tools will do anyway, does this change
> the preference profile between Hibernate's session-level cache vs. JCS? If
> so, how?
> 
> The bottom line, quite frankly, is that we're nervous about relying on JCS
> in the absence of some reassurances about its maturity and use in the real
> world, as JCS is clearly attempting to solve difficult engineering issues,

I wouldn't call JCS mature, but it works reasonably well for some
peoples needs, and is a good place to start for a distributed cache. But
because it has no consistency guarantee between nodes in the cache, I'm
not sure it is workable for O/R mapping and multiple nodes.

(However, I believe one could implement an auxilliary which provided
more consistency -- all the hooks should be there)


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