To deploy JBoss Cache as an MBean inside JBoss, you can copy the configuration xml file over to the deploy directory (from all configuration whereby the necessary jars are present). Under the standalone package etc/META-INF directory , there are example configuration files for different cache modes that can be used to deploy JBoss Cache as well.

To verify that your JBoss Cache MBean is deployed correctly, you can first check the log output under the command console. Next you can verify it from JBoss JMX console. Look for jboss.cache domain.

Accessing the JBoss Cache MBean is just like accessing any JBoss MBean. Here is a code snippet:

                  import org.jboss.mx.util.MBeanServerLocator;
                  import org.jboss.mx.util.MBeanProxyExt;
                  import org.jboss.cache.TreeCacheMBean;
                  import javax.management.MBeanServer;
                  ...

                  MBeanServer server;
                  TreeCacheMBean cache;

                  public init() throws Exception
                  {
                  try
                  {
                  server = MBeanServerLocator.locateJBoss();
                  cache = (TreeCacheMBean) MBeanProxyExt.create(TreeCacheMBean.class, "jboss.cache:service=TreeCache",
                  server);
                  }
                  catch (Exception ex)
                  {
                  // handle exception
                  }
                  }

                  public void myBusinessMethod()
                  {
                  Object value = cache.get("/my/node", "myKey");

                  HashMap stuff = new HashMap();
                  stuff.put("key1", "value1");
                  stuff.put("key2", "value2");
                  stuff.put("key3", "value3");

                  cache.put("/my/new/node", stuff);

                  cache.remove("/my/node");

                  ...
                  }

               

Yes. The JBoss Cache source code is also up to date on the jboss-3.2 CVS branch. However, only TreeCache is supported there since JBossAop (which PojoCache relies on) is only available in JBoss AS 4.x onwards.

Yes. There are some scenarios where you may want to run multiple instances of JBoss Cache. For example, you want to run multiple local cache instances with each instance having its own configuration (e.g., different cache policy). In this case, you will need multiple xml configuration files.

Yes. Since Hibernate 3.0 release, you can configure it to use JBoss Cache (namely, TreeCache) as a second level cache. For details, see Hibernate documentation, and also see http://wiki.jboss.org/wiki/Wiki.jsp?page=JBossCacheHibernate

Note that since Hibernate 3.0.2 and JBossCache 1.2.2, we have fixed a critical bug that depending on the usage pattern can cause deadlock during query caching.

It is not necessary to use PojoCache for second level cache inside Hibernate because Hibernate manages fine-grained fields in Java objects. So using PojoCache won't provide any advantage.

You can configure the JBoss Cache through a configuration xml file. Or you can set it programmatically through its get/set methods. Check with the documentation for both examples.

These are tags for deploying JBoss Cache as a JBoss MBean service. For consistency, we have kept them in the standalone package as well, specifically, the MBean tag. If you run in standalone mode, JBoss Cache will ignore these elements.

JBossCache has five different cache modes, i.e., LOCAL , REPL_SYNC , REPL_ASYNC , INVALIDATION_SYNC and INVALIDATION_ASYNC . If you want to run JBoss Cache as a single instance, then you should set the cache mode to LOCAL so that it won't attempt to replicate anything. If you want to have synchronous replication among different JBoss Cache instances, you set it to REPL_SYNC . For asynchronous replication, use AYSNC_REPL . If you do not wish to replicate cached data but simply inform other caches in a cluster that data under specific addresses are now stale and should be evicted from memory, use INVALIDATION_SYNC or INVALIDTAION_ASYNC . Synchronous and asynchronous behavior applies to invalidation as well as replication.

Note that ASYNC_REPL and INVALIDATION_ASYNC are non-blocking. This can be useful when you want to have another JBoss Cache serving as a mirror or backup and you don't want to wait for confirmation that this mirror has received your messages.

JBoss Cache leverages JGroups as a replication layer. A user can configure the cluster of JBoss Cache instances by sharing the same cluster name ( cluster name ). There is also an option of whether to populate the cache data upon starting a new instance in the ClusterConfig attribute.

Note that once all instances join the same replication group, every replication change is propagated to all participating members. There is no mechanism for sub-partitioning where some replication can be done within only a subset of members. This is on our to do list.

Yes, both will continue to run, but depending on your replication mode, all transactions or operations may not complete. If REPL_SYNC is used, operations will fail while if REPL_ASYNC is used they will succeed. Even if they succeed though, caches will be out of sync.

At this stage (JBoss Cache 1.x) the answer is no. We do have an abstraction layer between the communication suite and JBoss Cache in the pipelines, and this may appear as a feature at some stage in the future.

As of JBoss Cache 1.4.0, replication need not occur to every node in the cluster. This feature - called Buddy Replication - allows each node to pick one or more 'buddies' in the cluster and only replicate to its buddies. This allows a cluster to scale very easily with no extra impact on memory or network traffic with each node added.

See the User Guide for more information on Buddy Replication, and how it can be used to achieve very high scalability.

Yes. All the above mentioned properties are per cache instance. Therefore you will need a separate JBoss Cache instance.

Yes. They are both JGroups group names. Besides the notion of a channel in JGroups, it also can partition the channel into different group names.

There are two parameters to consider: multicast address (plus port) and the group name. At minimum, you will have to run components using a different group name. But whether to run them on the same channel depends upon whether the communication performance is critical for you or not. If it is, then it'd be best to run them on different channels.

Yes. Starting with release 1.1, JBoss Cache has a CacheLoader interface that supports cache persistence. See below.

Yes. Starting with release 1.2.4, JBoss Cache uses the CacheLoader to support cache passivation/ overflow. See documentation on how to configure and use this feature.

Yes, it is thread safe.

No, although it is also on our to do list. Our internal implementation does use a similar 2PC procedure to coordinate a transaction among different instances.

JBoss Cache supports any TransactionManager that is JTA compliant such as JBossTM. A user can configure the transaction manager through the configuration xml setting. JBossCache also has a built in dummy transaction manager ( org.jboss.cache.tm.DummyTransactionManager ) for testing purposes only. But note that DummyTransactionManager is not thread safe .i.e., it does not support concurrent transactions. Instead, only one transaction is allowed at a time.

You either use the default (JBoss) TransactionManager to run JBossCache inside JBoss, or you have to implement the TransactionManagerLookup interface, and return an instance of your javax.transaction.TransactionManager. The configuration property TransactionManagerLookupClass defines the class to be used by the cache to fetch a reference to a TransactionManager. It is trivial to implement this class to support other TransactionManagers. Once this attribute is specified, the cache will look up the transaction context from this transaction manager.

For the client code, here is a snippet to start and commit a transaction:

tx = (UserTransaction)new InitialContext(prop).lookup("UserTransaction");
                  tree = new TreeCache();
                  config = new PropertyConfigurator();
                  config.configure(tree, "META-INF/replSync-service.xml");

                  tx.begin()
                  tree.put(fqn, key, value);
                  tx.commit();
               

JBossCache lets you control the cache locking level through the transaction isolation level. This is configured through the attribute IsolationLevel . Currently, JBossCache employs pessimistic locking internally. And the transaction isolation level from the pessimist locking corresponds to JDBC isolation levels, namely, NONE , READ_UNCOMMITTED , READ_COMMITTED , REPEATABLE_READ , and SERIALIZABLE . Note that these isolation levels are ignored if optimistic locking is used. For details, please refer to the user manual.

By default JBoss Cache uses pessimistic locking to lock data nodes, based on the isolation level configured. Since JBoss Cache 1.3.0, we also offer optimistic locking to allow for greater concurrency at the cost of slight processing overhead and performance. See the documentation for a more detailed discussion on concurrency and locking in JBoss Cache.

Use the XMl attribute NodeLockingScheme . Note that IsolationLevel is ignored if NodeLockingScheme is set to OPTIMISTIC . Also note that NodeLockingScheme defaults to PESSIMISTIC if omitted.

First of all, JBossCache has a notion of root that serves as a starting point for every navigational operation. The default is "/" (since the default separator is "/" for the fqn). The locking then is applied to the node under root, for example "/org" (no locking "/").

Furthermore, let's say when JBossCache needs to apply a write lock on node "/org/jboss/test", it will first try to obtain read lock from the parent nodes recursively (in this example, "/org", and "/org/jboss"). Only when it succeeds then it will try to obtain a write lock on "/org/jboss/test".

Yes. JBossCache controls the individual node locking behavior through the isolation level semantics. This means even if you don't use a transaction, you can specify the lock level via isolation level. You can think of the node locking behavior outside of a transaction as if it is under transaction with auto_commit on.

If the updates are under transaction, then the broadcasts happen only when the transaction is about to commit (actually during the prepare stage internally). That is, it will be a batch update. However, if the operations are not under transaction context, then each update will trigger replication. Note that this has performance implication if network transport is heavy (it usually is).

If you do a cache.remove("/root"), it will recursively remove all the entries under "/root".

With JBoss Cache 1.3.0, you can if you are running JBoss Cache within JBoss AS or are using JDK 5.0's jconsole utility. See the chapter titled Management Information in the JBoss Cache user guide for more details.

Yes, you can. Set the UseInterceptorMbeans configuration attribute to false (this defaults to true ). See the chapter titled Management Information in the JBoss Cache user guide for more details.

jboss-serialization.jar is the JBoss Serialization library, which is much more efficient in terms of speed and CPU usage as well as the generated byte stream size than standard Java serialization. This very significantly improves replication performance of custom objects placed in the cache.

From 1.4.x, JBoss Cache relies on this library and it is needed to run JBoss Cache.

Yes you can, by passing in the -Dserialization.jboss=false environment variable to your JVM.

Not right now. JBoss Cache does not support partitioning that a user can configure to have different set of data residing on different cache instances while still participating as a replication group.

Application-specific classloading is used widely inside a J2EE container. For example, a web application may require a new classloader to scope a specific version of the user library. However, by default JBoss Cache is agnostic to the classloader. In general, this leads to two kinds of problems:

To solve the first kind of issue, in JBoss Cache 1.2.4 we introduced the concept of a TreeCacheMarshaller . Basically, this allows application code to register a classloader with a portion of the cache tree for use in handling objects replicated to that portion. See the TreeCacheMarshaller section of the user guide for more details.

To solve the second kind of issue, the only solution (that we know of) is to cache "serialized" byte code and only de-serialize it during every object get (and this will be expensive!). That is, during a put operation, the object instance will be serialized and therefore can be deserialized safely by a "foreign" classloader. However, the performance penalty of this approach is quite severe so in general another local in-vm version will need to be used as a "near-line" cache. Note also that each time the serialized bytes are deserialized, a new instance of the object is created.

To help with this kind of handling, JBoss has a utility class called MarshalledValue that wraps around the serialized object. Here is a code snippet that illustrates how you can create a wrapper around JBossCache to handle the classloader issue:

import org.jboss.invocation.MarshalledValue;

                  public class CacheService {
                  private TreeCache cache_;

                  public object get(Fqn fqn, String key) {
                  return getUnMarshalledValue(cache_.get(fqn, key));
                  }

                  public object set(Fqn fqn, String key, Object value) {
                  cache_.put(fqn, key, getMarshalledValue(value));
                  return value; // only if successful
                  }

                  ...

                  private Object getUnMarshalledValue(object value) {
                  // assuming we use the calling thread context classloader
                  return ((MarshalledValue)value).get();
                  }

                  private Object getMarshalledValue(Object value) {
                  return new MarshalledValue(value);
                  }
                  }

               

Yes. Starting with release 1.2.4, JBoss Cache has introduced ExtendedTreeCacheListener which takes in consideration pre and post event notification. See documentation for more details. Note that TreeCacheListener and ExtendedTreeCacheListener will be merged into TreeCacheListener in release 1.3.

You create a class (myListener) that extends AbstractTreeCacheListener and provide concrete implementation for the node events that you are interested in. Then you add this listener to the TreeCache instance on startup to listen to the events as they occur by calling TreeCache.addTreeCacheListener(myListener).

                  public class MyListener extends AbstractTreeCacheListener
                  {
                  ...

                  public void nodeModify(Fqn fqn, boolean pre, boolean isLocal) {
                  if(log.isTraceEnabled()){
                  if(pre)
                  log.trace("Event DataNode about to be modified: " + fqn);
                  else
                  log.trace("Event DataNode modified: " + fqn);
                  }
                  }

                  ...
                  }
               

Yes, you can. Originally, TreeCache Marshalling was designed as a workaround for those replicated caches that upon state transfer did not have access to the classloaders defining the objects in the cache.

On each deployment, JBoss creates a new classloader per the top level deployment artifact, for example an EAR. You also have to bear in mind that a class in an application server is defined not only by the class name but also its classloader. So, assuming that the cache is not deployed as part of your deployment, you could deploy an application and put instances of classes belonging to this deployment inside the cache. If you did a redeployment and try to do a get operation of the data previously put, this would result on a ClassCastException. This is because even though the class names are the same, the class definitions are not. The current classloader is different to the one when the classes were originally put.

By enabling marshalling, you can control the lifecycle of the data in the cache and if on undeployment, you inactivate the region and unregister the classloader that you'd have registered on deployment, you'd evict the data in the cache locally. That means that in the next deployment, the data won't be in the cache, therefore avoiding the problem. Obviously, using marshalling to get around this problem is only recommended when you have some kind of persistence backing where the data survives, for example using CacheLoaders, or when JBossCache is used as a second level cache in a persistence framework.

To implement this feature, please follow the instructions indicated in the example located in the TreeCacheMarshaller section of the user's guide. It's worth noting that instead of a ServletContextListener, you could add this code into an MBean that contained lifecycle methods, such as start() and stop(). The key would be for this MBean to depend on the target cache, so that it can operate as long as the cache is up and running.