Max Rydahl Andersen wrote:
So I started breaking out 3.3 as a separate code base on the Hibernate
svn trunk. The first thing done was this org.hibernate.cache.Cache
splitting. So at this point we now have the ability to be completely
free in how we cache entity-data versus collection-data versus
query-data versus timestamps-data within the same "second level cache".
Cool.
But now looking back at #1, I am no longer certain of the conclusions;
and to me the wiki did not make it clear to me what the "long term"
solution was supposed to be (nor really what the "short term" solution
is/was either). Anyone remember the specific conclusions with regards
to this point?
Long-term:
In Hibernate - use seperate caches which you have done for 3.3
In JBoss Cache - as it stands now you would have to use differnt
jbosscache configurations.
In older versions of JBC you would need different treecache.xml; but
that has been simplified
in later JBC's AFAIK - Manik/galder ? Depending on this and wether
optimistic locking is a global
or node level-and-down setting users might need some less or more
complex "writing jbosscache config files
for hibernate" examples ;)
Short-term:
Write a cacheprovider that would use different jbosscaches for each
"type" of cache.
Not sure if that still makes sense.
Manik can better comment on plans for having separate configurations
(e.g. optimistic vs pessimistic, invalidation vs replication) for
different regions of the cache. But, I know it's not a soonish thing.
That means if you want different behavior for the different "types" of
caches you need separate caches. If the JGroups multiplexer is
available, that's not too bad, as the caches can share a channel. If we
think it through well, they can likely share an overall config file,
with the different "types" just overriding a couple properties that are
relevant.
If the JGroups multiplexer isn't available then having a separate cache
for each "type" is a royal pain, since you have multiple channels that
need to have unique ports, etc. And we need to assume that the
multiplexer won't be available in any non-JDK5 env, since the earliest
JG release where it's reliable is 2.5.
Re: #4 : what exactly are these differences? Now is the time to merge
it back...
I recall these as being Bryan 2 things:
1) setting up JBC/Cacheprovider so it would use the correct classloader
when loading data from the cache.
2) doing some "mutations"/magic-lookup of the cache region names to know
which classloader to use
(this might just me having nightmares, so need Bryan to certify ;) If
it's true we would
need to look into the practicallity of that solution.
The issue here is that if you send a message to replicate type Foo, on
the remote node the thread coming up from JGroups that handles the
message needs access to the Foo class in order to deserialize Foo and
put it in the cache. Determining the correct classloader to use is a
problem if the cache is shared between multiple deployments. There's a
standard JBC API to handle this use case, as discussed at
http://labs.jboss.com/file-access/default/members/jbosscache/freezone/docs/1.4.1/TreeCache/en/html/treecache_marshaller.html.
The fix I did was just to 1) have the org.hibernate.cache.Cache impl
make use of this API and 2) prevent replication of the
org.hibernate.cache.StandardQueryCache region, since that region could
be shared between multiple deployments and hence there's no 'correct'
classloader. A diff between the EJB3 class and o.h.c.TreeCache is
attached. An equivalent thing was done for OptimisticTreeCache.
If we move to a mode where we have one cache (or set of caches) per
deployment, then this kind of stuff becomes unnecessary. But, again,
that requires the JGroups multiplexer.
Re: #5 : what about the other solution I proposed where instead of
registering synchs directly with the TC/TM, you instead delegate it to
a strategy which can route the request back through Hibernate;
Hibernate can then manage ordering the callbacks?
I don't recall more progress on that topic.
/max
Re: #6 : I'm actually in favor of just moving to the new (2.0) API;
easier from a management perspective.
Ok, so my notes from the call, based on issues from the wiki
1. Multiple caches will probably only formally make it in the next
major Hibernate release - 3.3.
2 Notes on putForExternalRead() functionality, in addition to the
solution presented on the wiki:
- PFER only goes through if node does not exist; no-op otherwise
- Force asynchronous mode for replication or invalidation to prevent
any blocking
- 0ms lock timeout to prevent any blocking here either. If this
fails, PFER is a no-op
- no to separate thread necessary, since we will be operating with a
0ms timeout, async replication and a no-op if the node exists. The
only real chance of any blocking here is JGroups FC which is
considered small enough a case.
3. Since JBC 1.4.1.SP1, write locks are not acquired on parents when
adding or removing children, to be more accurate to repeatable read
semantics. WLs can still be acquired on parents if enabled in the
configuration (see "LockParentForChildInsertRemove" in
http://labs.jboss.com/file-access/default/members/jbosscache/freezone/docs/1.4.1.SP2/TreeCache/en/html/configuration.html,
which defaults to false). As such, this contention should no longer
be a problem.
4. Brian implemented for EJB3 clustering in AS 4.2, will make it's
way back into HIbernate in the 3.3 timeframe?
5. Do nothing for now since the urgency is removed. Only fails on
old versions of JBoss TS. In future (JBC 2.1 timeframe) look at what
the microcontainer has to offer with synchronisation registrations.
6. Coordination issue
7. Galder to come back with more details here, but general consensus
is not to perform transparent retries.
Feel free to add stuff I may have missed or further thoughts.
Very useful and productive call!
Cheers,
Manik
--
Brian Stansberry
Lead, AS Clustering
JBoss, a division of Red Hat
[EMAIL PROTECTED]
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