[jboss-user] [JBoss Cache Users] - Memory growth even after pojo is deattached from pojo cache

anandhs do-not-reply at jboss.com
Mon Nov 16 12:40:29 EST 2009

Problem: PojoCache - huge memory usage even after detaching objects. Results in outofmemory (both Heap and non-Heap). Since it keeps increasing, bumping up the  memory and permgen is not a practical solution.

Summary: Running a stress test consisting of 3 objects. The lifespan of these objects is small (for the test) before they are removed from cache.

3 objects which need to stored - Order, Item, Attributes
Order has => map of Items, some long fields and an enum field.
Item => map of attributes, some long fields and an enum field.

The flow

   1. I create an Order, add Item to it. Then attach Order to pojocache. (Not using Attributes at this point). I use the attach(String, Object) method.
   2. The  order goes thru various state changes and so does Item. After order is "Completed" state it is detached from PojoCache. All done within a transaction.
   3. Since I am stress testing, I create about 4000 orders in 200 seconds, each Order takes about 10-20 seconds before it is completed and detached from PojoCache.
   4. Also note that all the changes to the objects are done using a task in a ScheduledThreadPoolExecutor. One task per Order, the task is resubmitted for each state change. I do not hold the task anywhere, after Order is "Completed" it is dereferenced.


   1. Heap memory contiues to grow at a steady rate peaking at abt 500 M (when the test is completed)
   2. Non Heap also continues to grow - peaking at abt 112M
   3. Almost a consistent slope for increase in memory
   4. If I run the same test without jboss cache and using an internal hashmap the memory consumption maxes at about 15 -20Mb.
   5. If I increase my load beyond a certain number I start running out of PermGen space.


   1. I expect memory should not continue to increase, or is the test small that the cache does not get a chance to cleanup, I did try manual GC at the end of the test, but that did not make any difference in the memory footprint
   2. So am I not doing something here? I am doing a detach of obects, anything else I need to do?
   3. Also are there any know issues around Out of PermGen memory. I could not find anything on the forums.

Test setup

   1. Java 1.6
   2. Jboss Pojo - 3.0
   3. JBoss core cache - 3.2.1
   4. Stand alone SE test.
   5. DummyTransactionManager

I ran a small test in Yourkit and notice the top object that retains memory are ( 94MB out od 110Mb)

Objects with biggest retained size

 Name 	 Retained Size 
org.jboss.aop.standalone.StandaloneClassPool	55,264,688	59 %
 java.util.Hashtable	54,637,584	58 %
 java.util.Hashtable$Entry[3071]	54,637,544	58 %
 sun.misc.Launcher$AppClassLoader [Held by JVM]	13,694,848	15 %
 java.util.Vector 	13,079,760	14 %
 java.lang.Object[5120]	13,079,736	14 %
org.jboss.aop.proxy.ClassProxyFactory	10,640,456	11 %
java.util.WeakHashMap	10,634,752	11 %
java.util.WeakHashMap$Entry[4096]	10,634,672	11 %
org.jboss.aop.instrument.Instrumentor	9,196,728	10 %

Things that I plan on trying in the meantime

    * use strings instead of enum
    * compiled aspects instead of runtime weaving
    * Use 3.0.3 version of pojocache instead of 3.2.1


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