RE: [Hibernate] Hibernate and JCS Questions

[Gavin K. <Gav...@ex...>]

> 2) What was the process by which Gavin gained sufficient=20
> confidence in JCS to include it in Hibernate?

Christian Muenier has done quite a lot of research and testing
with JCS and it was him who recommended use of JCS in Hibernate.
He has implied to me (privately) that he does not fully trust
JCS distributed caching.

> 3) Why does Gavin indicate that JCS can't be used in a=20
> clustered read-write environment, in contradiction to the JCS=20
> documentation?

Firstly, please understand that Hibernate is geared towards
highly transactional systems and is very very fussy about
ensuring that transaction isolation is always preserved. JCS
distributed caching was not designed with this kind of usage
in mind.

Secondly, to support that kind of strict transaction isolation,
Hibernate sits some metadata in on top of the cached
object. The way this is done is *not* safe for use with a
distributed cache.

Now, I fully understand that not all applications require this=20
level of transaction isolation and it sounds like your application=20
is one of those. Its quite easy to add a new caching strategy that=20
implements read-write caching with weaker isolation semantics.
(This should not take much development effort on your part.)
=20
> 4) If we were able to commit to using Hibernate in a=20
> read-only fashion and doing our data writing some other way,=20
> changing the data out from under Hibernate, which various=20
> legacy admin tools will do anyway, does this change the=20
> preference profile between Hibernate's session-level cache=20
> vs. JCS? If so, how?

Oh...nothing so extreme as that! All you would need is two
session factories, one with no cache, one with a read-only
cache (and a sufficiently short timeout) ... you don't need
To scrap Hibernate all together! But the correct solution
is simply to add a new implementation of=20
CacheConcurrencyStrategy.

> The bottom line, quite frankly, is that we're nervous about=20
> relying on JCS in the absence of some reassurances about its=20
> maturity and use in the real world, as JCS is clearly=20
> attempting to solve difficult engineering issues, and this=20

Hibernate has a pluggable caching architecture, though that's
not currently exposed to the user. If this is a critical issue
for you, you should probably spend a little while investigating
other cache implementations. It would *not* be difficult to plug
them into Hibernate.

Gavin


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