[Hibernate] CacheProviders

[Steve E. <ste...@jb...>]

Currently CacheProvider exposes a single method for Hibernate to obtain
a cache adapter (a Cache impl).  However, there are numerous ways in
which Hibernate uses the second level cache all of which have slightly
different semantics.  As of right now, Hibernate uses the second level
cache for the following:

1)       entity data cache

2)       collection data cache

3)       query results

4)       misc (UpdateTimestampsCache, e.g.)

=20

Of these, entity and collection data caches have different requirements
and semantics from, say, storing query results.  And the manner in which
update-timestamp info needs to be written into the cache is different
than all the others.  I've been thinking about splitting up these
abstractions to better align with how we actually use the cache
providers in these different scenarios.  Thus, on CacheProvider, instead
of just a single buildCache(...) method we would have separate methods
for the various use cases like buildEntityDataCache(),
buildCollectionDataCache(), buildQueryCache(), buildGeneralCache().
Additionally, we may want to split the Cache interface into separate
interfaces also based on usage; this would only be intended to allow
clearer definition of the capabilities allowed from each usage scenario.

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Another nice benefit of this would be to allow "mixed providers".  Like
imagine a clustered data cache along with a local query cache.

=20

Of course, this is a public extension API - so I wanted to put this out
there for discussion.