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• Will have to move the ehcache jar into common/lib
  • The Tomcat and RMI classloaders do not get along that well. Move ehcache.jar to $TOMCAT_HOME/common/lib. This fixes the problem. This issue happens with anything that uses RMI, not just ehcache.
  • There are lots of causes of memory leaks on redeploy. Moving ehcache and backport-util-concurrent out of the WAR and into $TOMCAT/common/lib fixes this leak.
  • This also means commons-logging and commons-collections (if used in terracota) have to go into common/lib
• Multicast and automatic discovery
  • Multicast Blocking
    The automatic peer discovery process relies on multicast. Multicast can be blocked by routers. Virtualisation technologies like Xen and VMWare may be blocking multicast. If so enable it. You may also need to turn it on in the configuration for your network interface card.
    An easy way to tell if your mutlicast is getting through is to use the ehcache remote debugger and watch for the heartbeat packets to arrive.
  • Multicast Not Progagating Far Enough or Propagating Too Far
    You can control how far the multicast packets propagate by setting the badly misnamed time to live. Using the multicast IP protocol, the timeToLive value indicates the scope or range in which a packet may be forwarded. By convention:
    0 is restricted to the same host
    1 is restricted to the same subnet
    32 is restricted to the same site
    64 is restricted to the same region
    128 is restricted to the same continent
    255 is unrestricted
    The default value in Java is 1, which propagates to the same subnet. Change the timeToLive property to restrict or expand propagation.
    • Reference: http://ehcache.sourceforge.net/documentation/distributed_caching.html
  • RMICachePeer may fail to start if there are spaces in the tomcat path (remove all spaces from the tomcat path)
    • Reference: http://ehcache.sourceforge.net/documentation/tomcat.html
• Default delivery mechanism for ehcache is RMI, this would seem to perform more poorly than some of the other lighter weight options like JXTA or JGroups but this needs to be tested
  • Some users have reported that enabling distributed caching causes a full GC each minute. This is an issue with RMI generally, which can be worked around by increasing the interval for garbage collection. The effect that RMI is having is similar to a user application calling System.gc() each minute. In the settings above this is disabled, but it does not disable the full GC initiated by RMI.
    The default in JDK6 was increased to 1 hour. The following system properties control the interval.
    -Dsun.rmi.dgc.client.gcInterval=60000
    -Dsun.rmi.dgc.server.gcInterval=60000
    See http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=4403367 for the bug report and detailed instructions on workarounds.
  • Some users have reported that enabling distributed caching causes a full GC each minute. This is an issue with RMI generally, which can be worked around by increasing the interval for garbage collection. The effect that RMI is having is similar to a user application calling System.gc() each minute. In the settings above this is disabled, but it does not disable the full GC initiated by RMI.
    The default in JDK6 was increased to 1 hour. The following system properties control the interval.
    -Dsun.rmi.dgc.client.gcInterval=60000
    -Dsun.rmi.dgc.server.gcInterval=60000
    See http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=4403367 for the bug report and detailed instructions on workarounds.
• Some recommended GC settings
  • -XX:+DisableExplicitGC - some libs call System.gc(). This is usually a bad idea and could explain some of what we saw.
  • -XX:+UseConcMarkSweepGC - use the low pause collector
  • -XX:NewSize=1/4 of total heap size -XX:SurvivorRatio=16
• Replication requires an object to be Serializable to replicate correctly
  • Non-serializable Objects can use all parts of ehcache except for DiskStore and replication. If an attempt is made to persist or replicate them they are discarded and a WARNING level log message emitted.
  • Elements attempted to be replicated or overflowed to disk will be Some recommended GC settings
  • -XX:+DisableExplicitGC - some libs call System.gc(). This is usually a bad idea and could explain some of what we saw.
  • -XX:+UseConcMarkSweepGC - use the low pause collector
  • -XX:NewSize=1/4 of total heap size -XX:SurvivorRatio=16
  • removed and a warning logged if not Serializable.
• Use TCP for reliability (instead of UDP)
• Shutting down the cache?
  • If the JVM keeps running after you stop using ehcache, you should call CacheManager.getInstance().shutdown() so that the threads are stopped and cache memory released back to the JVM. Calling shutdown also insures that your persistent disk stores get written to disk in a consistent state and will be usable the next time they are used.
  • If the CacheManager does not get shutdown it should not be a problem. There is a shutdown hook which calls the shutdown on JVM exit.
  • Ehcache should be shutdown after use. It does have a shutdown hook, but it is best practice to shut it down in your code.
    Shutdown the singleton CacheManager: CacheManager.getInstance().shutdown();
• Testing and checking the cache
  • Section 9 of the manual explains methods for measuring cache efficiency
• Upgrade to version 1.4.0 of ehcache (many advantages to using the newest version)

  Code Block
  xml xml
  <dependency> <groupId>net.sf.ehcache</groupId> <artifactId>ehcache</artifactId> <version>1.4.0</version> </dependency>

• Testing cache replication
  ehcache-1.x-remote-debugger.jar can be used to debug replicated cache operations. It is included in the distribution tarball for ehcache-1.2.3 and higher. It is invoked using:

  No Format
  java -jar ehcache-1.x-remote-debugger.jar path_to_ehcache.xml cacheToMonitor

  It will print a configuration of the cache, including replication settings and monitor the number of elements in the cache. If you are not seeing replication in your application, run up this tool to see what is going on.
  It is a command line application, so it can easily be run from a terminal session.

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