JBoss Enterprise Application Platform 4.2 JBoss Cache Frequently
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1. 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 Does JBoss Cache currently support pre event and post event notification Yes Starting with release 1 2 4 JBoss Cache has introduced ExtendedT reeCacheListener which takes in consideration pre and post event notification See documentation for more details Note that T reeCacheListener and ExtendedT reeCacheListener will be merged into T reeCacheListener in release 1 3 How do implement a custom listener to listen to TreeCache events You create a class myListener that extends AbstractT reeCacheListener 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 addT reeCacheListener myListener Chapter 2 JBoss Cache Tree Cache 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 Can use useRegionBasedMar shalling attribute in JBoss Cache in order to get around ClassCastExceptions happening when accessi2. I redhat JBoss Enterprise Application Platform 4 2 JBoss Cache Frequently Asked Questions for Use with JBoss Enterprise Application Platform 4 2 Edition 1 0 Ben Wang Bela Ban Manik Surtani Scott Marlow Galder Zamarreno JBoss Enterprise Application Platform 4 2 JBoss Cache Frequently Asked Questions for Use with JBoss Enterprise Application Platform 4 2 Edition 1 0 Ben Wang Bela Ban Manik Surtani Scott Marlow Galder Zamarre o Legal Notice Copyright 2010 Red Hat Inc This document is licensed by Red Hat under the Creative Commons Attribution ShareAlike 3 0 Unported License If you distribute this document or a modified version of it you must provide attribution to Red Hat Inc and provide a link to the original If the document is modified all Red Hat trademarks must be removed Red Hat as the licensor of this document waives the right to enforce and agrees not to assert Section 4d of CC BY SA to the fullest extent permitted by applicable law Red Hat Red Hat Enterprise Linux the Shadowman logo JBoss MetaMatrix Fedora the Infinity Logo and RHCE are trademarks of Red Hat Inc registered in the United States and other countries Linux is the registered trademark of Linus Torvalds in the United States and other countries Java is a registered trademark of Oracle and or its affiliates XFS is a trademark of Silicon Graphics International Corp or its subsidiaries in the United States and or o
3. POJO is managed by the cache all cache operations are transparent Therefore all the usual in VM POJO method semantics are still preserved providing ease of use For example if a POJO has been put in PojoCache by calling putObject for example then any get set method will be intercepted by PojoCache to provide the data from the cache What s the relationship between PojoCache and TreeCacheAop classes Since release 1 4 we have created a new class called PojoCache to better reflect the cache nature The old implementation T reeCacheAop has been deprecated Does PojoCache have all the functional capabilities of TreeCache Yes PojoCache extends TreeCache so it has all the same features TreeCache such as cache mode transaction isolation level and eviction policy What is the difference between TreeCache and PojoCache Think of PojoCache as a TreeCache on steroids Seriously both are cache stores one is a generic cache and the other other one POJO Cache However while TreeCache only provides pure object reference storage e g put FQN fqn Object key Object value PojoCache goes beyond that and performs fine grained field level replication object mapping and relationship management for a user behind the scenes As a result if you have complex object systems that you would like to cache you can have PojoCache manage it for you You simply treat your object systems as they are residing in memory e g use your regular POJO m
4. 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 bya 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 11 a N s Enterprise Application Platform 4 2 JBoss Cache Frequently Asked Questions To help with this kind of handling JBoss has a utility class called Mar shalledValue 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
5. to run PojoCache Can PojoCache run as a MBean as well Yes It is almost the same as TreeCache MBean The only difference is the object name and the class name E g instead of lt mbean code org jboss cache TreeCache name jboss cache service TreeCache gt you will have lt mbean code org jboss cache aop PojoCache name jboss cache service PojoCache gt in the xml configuration file Can pre compile the aop classes such that I don t need to use the system classloader and jboss aop configuration xml Yes The latest versions of JBossCache have a pre compiler option called aopc You can use this option to pre compile your aspectized POJO Once the classes have been byte code generated they can be treated as regular class files i e you will not need to include any jboss aop xm1 that specifies the advisable POJO and to specify the JBossAop system class loader For an example of how to use aopc please see 1 tools directory for PojoCacheT asks14 xml and PojoCacheT asks50 xml Both contain Ant tasks that you can import to your regular project for annoc and aopc In addition please also check out the examples directory for concrete examples How do I use aopc on multiple module directories In aopc you specify the src path for a specific directory To pre compile multiple ones you will need to invoke aopc multiple times What s in the jboss aop xm1 configuration jboss aop xm1 is needed for POJO instrumen
6. 4 2 JBos m ss Cache Frequently d Questions 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 Can I plug in library X instead of JGroups to handle remote calls and group communications 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 Does the cache need to replicate to every other instance in the cluster Isn t this slow if the cluster is large 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 If I have the need for different TreeCache properties e g CacheMode and IsolationLevel do I simply need to create multiple TreeCache instances with the appropriate configuration Yes All the above mentioned properties are per cache instance T herefore you will
7. Cache outside of JBoss Application Server Of course JBoss Cache comes in two flavors Integrated with JBoss Application Server as an MBean service Standalone that can run in any Java EE server such as BEA WebLogic or IBM Websphere Of course it can also run in a standalone Java process i e outside Java EE context Where can I report bugs or problems Please report any bugs or problems to JBoss Cache User Forum Chapter 2 JBoss Cache Tree Cache Chapter 2 JBoss Cache Tree Cache Q A How do I deploy JBoss Cache as a MBean service To deploy JBoss Cache as an MBean inside JBoss you can copy the configuration xml file over to the deploy directory from a11 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 How do know if my JBoss Cache MBean has been deployed 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 How do I access the JBoss Cache MBean Accessing the JBoss Cache MBean is just like accessing any JBoss MBean Here is a code snippet JBoss Enterprise Applicati n Platform 4 7 JBoss Cache Erequently Asked O In Platiorm 4 2 JBOSS Cache Frequently Asked Q import org jboss mx util MBeanS
8. can also grab snapshots from the JBoss CVS repository see this wiki page the module name is JBossCache How do I build JBoss Cache from CVS sources To build do sh build sh jar This will produce jboss cache jar in the dist lib directory Or if you want to build the standalone package do sh build sh dist this will produce dist jboss cache dist zip Note that you will need to use JDK 5 0 to build the distribution You can still use the binaries you build with J2SE 1 4 x though Which JVMs are supported by JBoss Cache JBoss Cache has been tested and supported on J2SE 1 4 x and JDK 5 0 On jboss 3 2 CVS tree it also compiles on JDK1 3 but there is no official support for this version and using this is not recommended From JBoss Cache 1 3 0 onwards there is a new directory 1ib 50 what is it From JBoss Cache 1 3 0 onwards we support the use of Java 5 annotations used by PojoCache JBoss Enterprise Application Platform 4 2 JBoss Cache Frequently Asked Questions As a result there are jboss aop jdk50 jar and jboss cache jdk50 jar that are needed to work with the Java 5 annotations You will need to replace jboss aop jar and jboss cache jar in the lib directory with the 3j dk50 versions if you intend to use PojoCache Java 5 and annotations How do I know the version of JBoss Cache that am using Since release 1 2 you can check the jar version by running java jar jboss cache jar org jboss cache Version Can I run JBoss
9. chronized temporarily But when a user tries to obtain the cached contents of an evicted node and finds out that is null e g get returns null it should get it from the other data source and re populate the data in the cache During this moment the node content will be propagated and the cache content will be in sync However you still can run eviction policies with cache mode set to either REPL_SYNC or REPL_ASYNC Depending on your use case you can set multiple cache instances to have their own eviction policy which are applied locally or just have selected instances with eviction policies activated Also note that with cache loader option a locally evicted node can also be persisted to the backend store and a user can retrieve it from the store later on Q Does JBoss Cache support Region Yes JBoss Cache has the notion of region where a user can configure the eviction policy parameters e g maxNodes or timeToIdleSeconds A region in JBoss Cache denotes a portion of tree hierarchy e g a fully qualified name FQN For example a user can define org jboss and org foocom as two separate regions But note that you can configure the region programmatically now i e everything has to be configured through the xml file Q What are the EvictionPolicyConfig tag parameters for org jboss cache eviction LRUPolicy A They are 20 Table 4 1 Parameters wakeUplntervalln Seconds region maxNodes timeT oLivelnSecon
10. ds Chapter 4 Eviction Policies Interval where the clean up thread wakes to process the sitting queue and sweep away the old data A area where each eviction policy parameters are specified Note that it needs a minimum of _default region Max number of nodes allowed in the eviction queue 0 means no limit Age in seconds for the node to be evicted in the queue O denotes no limit I have turned on the eviction policy why do I still get out of memory OOM exception OOM can happen when the speed of cache access exceeds the speed of eviction policy handling timer Eviction policy handler will wake up every wakeUpIntervalInSeconds seconds to process the eviction event queue And the queue size is fixed at 20000 now So when the queue size is full it will create a backlog and cause OOM to happen unless the eviction timer catches up To address this problem in addition to increase the VM heap size you can also reduce the wakeUpIntervaleInSeconds so the timer thread processes the queue more frequently We will also externalize the queue size so it will be configurable in the next release 21 JBoss Enterprise Application Platform 4 2 JBoss Cache Frequently Asked Questions Chapter 5 Cache Loaders Q A 22 What is a CacheLoader A CacheLoader is the connection of JBossCache to a persistent data store The CacheLoader is called by JBoss Cache to fetch data from a store when that data is not in the cache and wh
11. eeCache Chapter 2 JBoss Cache Tree Cache as a second level cache For details see Hibernate documentation and also see http wiki jboss org wiki Wiki jsp page JBoss CacheHibernate 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 What about using PojoCache as a Hibernate cache 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 How can I configure JBoss Cache 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 In the configuration xml file there are tags such as class MBean etc What are these 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 What is the difference between the different cache modes JBossCache has five different cache modes i e LOCAL REPL SYNC REPL ASYNC INVALIDAT ION SYNC and INVALIDAT ION_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
12. elds with these modifiers That is it won t put these fields into Ahaia a Dage Cache Daia tarka Chapter 3 JBoss Cache Pojo Cache the cache and thus no replication either What are those keys such as JBoss internal class and AOPInstance They are for internal use only Users should ignore these keys and values in the node hashmap What about Collection classes Do I need to declare them prepared No Since the Collection classes such as ArrayList are java util classes aop by default won t instrument these classes Instead PojoCache will generate a dynamic class proxy for the Collection classes upon the put0bject call is invoked The proxy will delegate the operations to a cache interceptor that implements the actual Collection classes APIs That is the system classes won t be invoked when used in PojoCache Internally the cache interceptor implements the APIs by direct interaction with respect to the underlying cache store Note that this can have implications in performance for certain APIs For example both ArrayList and LinkedList will have the same implementation Plan is currently underway to optimize these APIs How dol use List Set and Map dynamic proxy PojoCache supports classes extending from List Set and Map without users to declare them aspectized It is done via a dynamic proxy Here is a code snippet to use an ArrayList proxy class ArrayList list new ArrayList list add first cache pu
13. en modifications are made to data in the cache the CacheLoader is called to store those modifications back to the store In conjunction with eviction policies JBoss Cache with a CacheLoader allows a user to maintain a bounded cache for a large backend datastore Frequently used data is fetched from the datastore into the cache and the least used data is evicted in order to provide fast access to frequently accessed data This is all configured through XML and the programmer doesn t have to take care of loading and eviction JBoss Cache currently ships with several CacheLoader implementations including FileCacheLoader this implementation uses the file system to store and retrieve data JBoss Cache nodes are mapped to directories subnodes to subdirectories etc Attributes of a node are mapped to a file data inside the directory BdbjeCacheLoader this implementation is based on the Sleepycat Java Edition database a fast and efficient transactional database It uses a single file for the entire store Note that if you use Sleepycat s CacheLoader with JBoss Cache and wish to ship your product you will have to acquire a commercial license from Sleepycat JDBCCacheLoader this implementation uses the relational database as the persistent storage ClusteredCacheLoader this implementation queries the rest of the cluster treating other servers in memory state as a data store And more See the documentation for more details Can writin
14. en offline when the first node is started again the data previously saved will still be available e g a shopping cart A caching web proxy a la Squid all data are contents of URLs users access the proxy and if the URL is not in the cache the CacheLoader fetches it from the web This could actually be a replicated and transactional version of Squid How do configure JBossCache with a CacheLoader Through XML both the fully qualified classname of the CacheLoader and its configuration string have to be given JBossCache will then instantiate a CacheLoader See JBossCache documentation for details Do have to pay to use Sleepycat s CacheLoader Not if you use it only for personal use As soon as you distribute your product with BdbjeCacheLoader you have to purchase a commercial license from Sleepycat See details at http www sleepycat com jeforjoosscache Can I use more than one cache loader As of JBossCache 1 3 0 yes With the new CacheLoaderConfiguration XML element see user manual section on cache loaders you can now describe several cache loaders The impact is that the cache will look at all of the cache loaders in the order they ve been configured until it finds a valid non null element of data When performing writes all cache loaders are written to except if the ignoreModifications element has been set to true for a specific cache loader Why do cache loaders go into an inconsistent state when I use transaction
15. eral Information Please to be building now Q A What is JBoss Cache JBoss Cache is a replicated and transactional cache It is replicated since multiple JBoss Cache instances can be distributed either within the same JVM or across several JVMs whether they reside on the same machine or on different machines on a network and data is replicated across the whole group It is transactional because a user can configure a JTA compliant transaction manager and make the cache operation transactional Note that the cache can also be run without any replication this is the local mode Currently JBoss Cache consists of two components a generic cache implemented internally as org jboss cache TreeCache and a POJO cache implemented internally as org jboss cache aop PojoCache TreeCache is a tree structured cache that provides replication and transaction context while Poj oCache extends the functionality of TreeCache but behaves as a true object cache providing transparent and finer grained object mapping into internal cache Who are the JBoss Cache developers JBossCache has been developed by Bela Ban Ben Wang Harald Gliebe Manik Surtani and Brian Stansberry Manik is the lead on JBoss Cache and Ben is the lead on PojoCache What is the license for JBoss Cache JBoss Cache is licensed under LGPL Where can download JBoss Cache The JBoss Cache product download page has prebuilt binaries as well as source distributions You
16. erverLocator 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 Can I run JBoss Cache on JBoss AS 3 2 x releases 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 Can I run multiple JBoss Cache instances on the same VM 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 Can TreeCache run as a second level cache inside Hibernate Yes Since Hibernate 3 0 release you can configure it to use JBoss Cache namely Tr
17. ethods without worrying about cache management Furthermore this is true in replication mode as well What are the steps to use the PojoCache feature Starting from release 1 3 depends on the JDK you use it has slightly different steps But in general in order to use PojoCache you will need to prepare POJO You can do either via xml declaration or annotation For annotation you can use either the JDK1 4 style or JDK50 one of which is part of JVM spec If you use JDK14 you will also need a annotation pre compiler annoc to pre process it instrumentation You will need to instrument your POJO either at compile time or load time If you do it during compile time you use so called aop pre compiler aopc to do bytecode manipulation If you do it via load time however you need either a special system class loader or in JDK50 you can use the javaagent option So if you use JDK50 for example with annotation and load time instrumentation then you won t Phan aba APA Cache ANA maak Chapter 3 JBoss Cache Pojo Cache need any pre processing step to use PojoCache For a full example please refer to the distro examples directory T here are numerous PojoCache examples that uses different options Can I run PojoCache in JBoss AS 3 2 x application server Yes and no Yes since JBossAop can also be back ported to 3 2 x see JBossAop wiki for details However it will take some effort T herefore the recommended JBoss version is 4 x
18. g jboss test 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 Can use the cache locking level even without a transaction context 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 With replication REPL_SYNC REPL_ASYNC or invalidation INVALIDATION_SYNC INVALIDATION_ASYNC how often does the cache broadcast messages over the network 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
19. g to CacheLoaders be asynchronous As of JBossCache 1 2 4 yes Set the CacheLoaderAsynchronous property to true See the JBossCache documentation for a more detailed discussion By default though all cache loader writes are synchronous and will block Can I write my own CacheLoader Yes A CacheLoader is a class implementing org jboss cache l1loader CacheLoader It is configured via the XML file see JBoss Cache and Tutorial documentation Does a CacheLoader have to use a persistent store No a CacheLoader could for example fetch and possibly store its data from a webdav capable webserver Another example is a caching proxy server which fetches contents from the web Note that an implementation of CacheLoader may not implement the store functionality in this case but just the load functionality What can use a CacheLoader for Some applications HTTP sessions can be persisted besides being replicated by JBossCache The Chapter 5 Cache Loaders CacheLoader can be configured to be shared or unshared meaning that every node in a cluster has its own local store It is also possible to attach a CacheLoader to just one of the nodes Simple persistence for POJOs Use of JBossCache aop and a local CacheLoader persist POJOs transparently into the store provided by the CacheLoader Highly available replicated and persisted data store The service is up as long as at least 1 node is running but even if all nodes are tak
20. he to manage it the Cache will dynamically swap out the regular Collection references with the dynamic proxy ones As a result it is transparent to the users What happens when my aspectized POJO has field members that are of Collection class When a user puts a POJO into the cache through the call put0bj ect it will recursively map the field members into the cache store as well When the field member is of a Collection class e g List Set or Map PojoCache will first map the collection into cache Then it will swap out dynamically the field reference with an corresponding proxy reference This is necessary so that an internal update on the field member will be intercepted by the cache What are the limitation of Collection classes in PojoCache Use of Collection class in PojoCache helps you to track fine grained changes in your collection fields automatically However current implementation has the follow limitation that we plan to address soon Currently we only support a limited implementation of Collection classes That is we support APIs in List Set and Map However since the APIs do not stipulate of constraints like NULL key or value it makes mapping of user instance to our proxy tricky For example ArrayList would allow NULL value and some other implementation would not The Set interface maps to java util HashSet implementation The List interface maps to java util ArrayList implementation The Map interface maps to
21. if network transport is heavy it usually is How can I do a mass removal If you do a cache remove root it will recursively remove all the entries under root Can I monitor and manage the JBoss Cache 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 Can I disable JBoss Cache management attributes in JBoss Cache 1 3 0 Yes you can Set the UseInterceptorMbeans configuration attribute to false this defaults to Chapter 2 JBoss Cache Tree Cache true See the chapter titled Management Information in the JBoss Cache user guide for more details What is jboss serialization jar introduced in JBoss Cache 1 4 x and do I need this 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 Can disable JBoss Serialization and revert back to standard Java serialization Yes you can by passing in the DSerialization jboss false environment variable to your JVM Does JBoss Cache support partitioning Not right now JBoss Cache does not support pa
22. java util HashMap implementation Another related issue is the expected performance For example the current implementation is ordered so that makes insert delete from the Collection slow Performance between Set Map and List collections also vary Adding items to a Set is slower than a List or Map since Set does not allow duplicate entries What are the pros and cons of PojoCache Chapter 3 JBoss Cache Pojo Cache A As mentioned in the reference doc PojoCache has the following advantages Fine grained replication and or persistency If you use a distributed PojoCache and once your POJO is put in the cache store there is no need to use another API to trigger your changes Furthermore the replication are fine grained field level Note this also applies to persistency Fine grained replication can have potential performance gain if your POJO is big and the changes are fine grained e g only to some selected fields POJO can posses object relationship e g multiple referenced Distributed PojoCache will handle this transparently for you And here are some cases that you may not want to use PojoCache You use only cache That is you don t need replication or persistency T hen since everything is operated on the in memory POJO reference there is no need for PojoCache You have simple and small POJOs Your POJO is small in size and also there is no object relationship then PojoCache possess not clear advantage to plain cache Y
23. need a separate JBoss Cache instance Does the Tree Cache config ClusterName have any relation to the JBoss AS cluster PartitionName 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 When using multiple JGroups based components cluster service xml treecache multiple instance s what is the correct valid way to configure those components to make sure my multicast addresses don t conflict 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 Does JBoss Cache currently support cache persistence storage Yes Starting with release 1 1 JBoss Cache has a CacheLoader interface that supports cache persistence See below Does JBoss Cache currently support cache passivation overflow to a data store Chapter 2 JBoss Cache Tree Cache 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 Is JBoss Cache thread safe Yes it is thread safe Does JBoss Cache support XA 2PC transactions now No although it is also on our to do list O
24. ng data in the cache that has just been redeployed 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 T his 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 survi
25. our application is bounded by memory usage Because PojoCache need almost twice as much of memory the original POJO in memory space and also the additional cache store for the primitive fields you may not want to use PojoCache Your POJO lifetime is short That is you need to create and destroy your POJO often Then you need to do pubObject and removeObject often it will be slow in performance 19 JBoss Enterprise Application Platform 4 2 JBoss Cache Frequently Asked Questions Chapter 4 Eviction Policies Q Does JBoss Cache support eviction policies A Yes JBoss Cache currently implements a LRU eviction policy for both TreeCache org jboss cache eviction LRUPolicy and PojoCache org jboss cache aop eviction AopLRUPolicy Users can also plug in their own eviction policy algorithms See user manual for details Currently there is user contributed policy called FIFOPolicy that evicts the node based on FIFO principle only Q Why can t Iuse org jboss cache eviction LRUPolicy for PojoCache as well A For PojoCache you will need to use org jboss cache aop eviction AopLRUPolicy because AOP has its eviction algorithm although is LRU but has totally different notion of an object for example Does JBoss Cache s implemented LRU eviction policy operates in replication mode Yes and no The LRU policy only operates in local mode That is nodes are only evicted locally This may cause the cache contents not to be syn
26. ree META INF replSync service xm1 tx begin tree put fqn key value tx commit How do I control the cache locking level 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 REPEAT ABLE_READ and SERIALIZABLE Note that these isolation levels are ignored if optimistic locking is used For details please refer to the user manual How does JBoss Cache lock data for concurrent access D He O s Enterprise Application Platform 4 2 JBoss Cache Frequently Asked Questions 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 How do I enable Optimistic Locking in JBoss Cache Use the XMI attribute NodeLockingScheme Note that IsolationLevel is ignored if NodeLockingSchene is set to OPT IMISTIC Also note that NodeLockingScheme defaults to PESSIMISTIC if omitted How does the write lock apply to an Fqn node say or
27. rtitioning that a user can configure to have different set of data residing on different cache instances while still participating as a replication group Does JBoss Cache handle the concept of application classloading inside say a J2EE container 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 Object instance is stored in cache1 and replicated to cache2 As a result the instance in cache2 is created by the system classloader The replication may fail if the system classloader on cache2 does not have access to the required class Even if replication doesn t fail a user thread in cache2 may not be able to access the object if the user thread is expecting a type defined by the application classloader Object instance is created by thread 1 and will be accessed by thread 2 with two different classloaders JBossCache has no notion of the different classloaders involved As a result you will have a ClassCastException This is a standard problem in passing an object from one application space to another JBossCache just adds a level of indirection in passing the object To solve the first kind of issue in JBoss Cache 1 2 4 we introduced the concept of a TreeCacheMarshaller Basically this allows
28. s pessimistic locking and attempt to read a node after removing it from within the same transaction scope This is a known bug see JBCACHE 477 and JBCACHE 352 which have been fixed in JBoss Cache 1 4 0 A very simple workaround if you re using JBoss Cache 1 3 x is to use optimistic locking One of the consequences of this bug is that for example if you use PojoCache with pojos that have private references to a List and you update and remove someelements of that List within a transaction when using pessimistic locking and a cache loader you may see lllegalStateExceptions thrown 23 JBoss Enterprise Application Platform 4 2 JBoss Cache Frequently Asked Questions Chapter 6 Troubleshooting Q lamhaving problems getting JBoss Cache to work where can I get information on troubleshooting A Troubleshooting section can be found in the following wiki link 24 Revision History Revision 1 1 4 402 Fri Oct 25 2013 Rebuild with Publican 4 0 0 Revision 1 1 4 1 2013 06 11 Rebuild for updated legal template Revision 1 1 4 2012 07 18 Rebuild for Publican 3 0 Revision 1 1 0 Thu Jun 03 2010 Updated versions for new doc structure Revision History Rudiger Landmann Misty Stanley Jones Anthony Towns Laura Bailey 25
29. t this field under management The second one Serializable when applied will cause PojoCache to treat the field as a Serializable object even when it is PojoCacheable What about compile time vs load time instrumentation then Again it depends But my preference is to do compile time instrumentation via aopc prefer this approach because it is easier to debug at least at the development stage In addition once generate the new class there is no more steps needed Is it possible to store the same object multiple times but with different Fqn paths Like lfoolbyName and foo byld Yes you can use PojoCache to do that It supports the notion of object reference PojoCache manages the unique object through association of the dynamic cache interceptor Do I need to declare all my objects prepared in jboss aop xml Not necessarily If there is an object that you don t need the cache to manage for you you can leave it out of the declaration The cache will treat this object as a primitive type However the object will need to implement Serializable interface for replication Can the cache aop intercept update via reflection No The update via reflection will not be intercepted in JBossAop and therefore PojoCache will not be able to perform the necessary synchronization When I declare my POJO to be aspectized what happens to the fields with transient static and final modifiers PojoCache currently will ignore the fi
30. tObject list test list Put the list under the aop cache list add second Won t work since AOP intercepts the dynamic proxy not the original POJO ArrayList myList List cache getObject list test we are getting a dynamic proxy instead myList add second it works now myList add third myList remove third What is the proper way of assigning two different keys with Collection class object Let s say you want to assign a List object under two different names you will need to use the class proxy to insert the second time to ensure both are managed by the cache Here is the code snippet BEN mj JBoss Enterprise Application Platform 4 2 JBo s Cache Frequently Asked Questions ArrayList list new ArrayList list add first cache putObject list list Put the list under the aop cache ArrayList myList List cache getObject list we are getting a dynamic proxy instead myList add second it works now cache putObject list_alias myList Note you will need to use the proxy here myList remove second OK so know I am supposed to use proxy when manipulating the Collection classes once they are managed by the cache But what happens to Pojos that share the Collection objects e g a List instance that is shared by 2 Pojos Pojos that share Collection instance references will be handled by the cache automatically That is when you ask the Cac
31. tation In jboss aop xm1 you can declare your POJO e g Person to be prepared a JBossAop term to denote that the object will be aspectized by the system After this declaration JBossAop will invoke any interceptor that associates with this POJO PojoCache will dynamically add an org jboss cache aop CacheInterceptor to this POJO to perform object mapping and relationship management Note that to add your POJO you should declare all the fields to be prepared as in the example a O s Enterprise Application Platform 4 2 JBoss Cache Frequently Asked Questions Can use annotation instead of the xml declaration Yes starting with JBossCache 1 3 you can use annotation to instrument your POJO for both JDK1 4 and 1 5 Check the documentation for details What are the pro and con of xml vs annotation It really depends on your organization environment I d say since this can be turned into a hot debate Having said that feel strongly that POJO annotation is well suited for PojoCache This is because once you specify the annotation you d probably change it rarely since there is no parameters to tune for example What are the org jboss cache aop annotation Transient and org jboss cache aop annotation Serializable field level annotations Starting in 1 4 we also offer two additional field level annotations The first one Transient when applied has the same effect as declaring a field transient PojoCache won t pu
32. ther countries MySQL is a registered trademark of MySQL AB in the United States the European Union and other countries Node js is an official trademark of Joyent Red Hat Software Collections is not formally related to or endorsed by the official Joyent Node js open source or commercial project The OpenStack Word Mark and OpenStack Logo are either registered trademarks service marks or trademarks service marks of the OpenStack Foundation in the United States and other countries and are used with the OpenStack Foundation s permission We are not affiliated with endorsed or sponsored by the OpenStack Foundation or the OpenStack community All other trademarks are the property of their respective owners Abstract This book is a compilation of frequently asked questions about JBoss Cache for use with JBoss Enterprise Application Platform 4 2 and its patch releases Table of Contents Chapter 1 General Information 2 3 Chapter 2 JBoss Cache Tree Cache 22 cen enn een een eens 5 Chapter 3 JBoss Cache Pojo Cache ec cce ten tn eee nee 14 Chapter 4 Eviction Policies 6 0 0 cnt n tne ene 20 Chapter 5 Cache Loaders u 2 0 22 22 nnn tne nee e eens 22 Chapter 6 Troubleshooting 0 ccc teen ete e tne ene ene 24 Revision History NAAN ASK te ek Reh EA A A dh es 25 JBoss Enterprise Application Platform 4 2 JBoss Cache Frequently Asked Questions Chapter 1 General Information Chapter 1 Gen
33. ur internal implementation does use a similar 2PC procedure to coordinate a transaction among different instances Which TransactionManagers are supported by JBoss Cache JBoss Cache supports any T ransactionManager that is JTA compliant such as JBossT M A user can configure the transaction manager through the configuration xml setting JBoss Cache also has a built in dummy transaction manager org jboss cache tm DummyT ransactionManager 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 How do I set up the cache to be transactional You either use the default JBoss T ransactionManager to run JBossCache inside JBoss or you have to implement the TransactionManager Lookup interface and return an instance of your javax transaction T ransactionManager 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 t
34. ves 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 13 JBoss Enterprise Application Platform 4 2 JBoss Cache Frequently Asked Questions Chapter 3 JBoss Cache Pojo Cache Q A 14 What is PojoCache PojoCache currently implemented PojoCache as a sub class of TreeCache is a fine grained field level replicated and transactional POJO plain old Java object cache By POJO we mean that the cache 1 automatically manages object mapping and relationship for a client under both local and replicated cache mode 2 provides support for inheritance relationship between aspectized POJOs By leveraging the dynamic AOP in JBossAop it is able to map a complex object into the cache store preserve and manage the object relationship behind the scene During replication mode it performs fine granularity i e on a per field basis update and thus has the potential to boost cache performance and minimize network traffic From a user perspective once your
35. 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 INVALIDAT ION SYNC or INVALIDT AION_ASYNC Synchronous and asynchronous behavior applies to invalidation as well as replication Note that ASYNC_REPL and INVALIDAT ION_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 How does JBoss Cache s replication mechanism work 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 ClusterConf ig 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 l run a 2 node cluster If the network dies do the caches continue to run 1IRnpcee Entarnrica Annlicatinn Platarm 42 1RA JBoss Enterprise Application Platform
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