Configuring the memory leak policy

You can configure WebSphere Application Server to detect, prevent, and take action, if possible, on classloader memory leaks by using the memory leak detection policy.

Before you begin

The leak detection policy for the WebSphere® Application Server is turned off by default. You can configure a leak detection, prevention, and action policy to accommodate your applications and environment so that potential memory leaks are reported and acted upon. Leak detection, prevention, and proactive fixing provides for protection and resiliency for servers that face persistent out of memory errors. When a classloader memory leak is detected, WebSphere® Application Server notifies you with informational messages in the log and by taking JVM heapdumps so that you can troubleshoot the problem. Optionally, you might also choose to have WebSphere Application Server mitigate, and if possible, fix the memory leak using reflection and other techniques.

A common error in Java™ Platform, Enterprise Edition (Java EE) applications is a classloader memory leak. A memory leak can result from subtle application bugs or a more complex use, such as third party libraries. System resources, such as CPU time due to garbage collection and the Java heap are consumed when a leak is present. A system can become unresponsive even though all other resources are available. Unless a protection and early warning system is built in, the system might remain in this degraded state and ultimately die due to an out of memory error.

For more information about memory leaks, see the Memory Leaks in Java Platform, Enterprise Edition applications topic.

About this task

The leak detection option is disabled by default. You can use Java virtual machine (JVM) custom properties to adjust the leak policy values, such as, enable and disable leak detection, action, and prevention. These custom properties are only applicable to a stand-alone server or managed application server and not to a node agent, admin agent, job manager, or deployment manager. When the application or the server is shutting down, WebSphere Application Server determines the classloaders that have leaked and are held references to all of associated loaded classes and objects. If a classloader leak is detected, a heapdump or systemdump is taken.

All persistent configurations of this service are completed using JVM custom properties. There are no administrative console panels. At runtime, use the MemoryLeakConfig and MemoryLeakAdmin mbeans for configuration and administration respectively; however, the configuration changes are not persisted until JVM custom properties are configured.

The MemoryLeak service and its mbean are active only in an application server that hosts applications and services requests. This service is not active on a Deployment Manager, node agent, administrative agent, or other servers types like WebSphere proxy server and so on.

Tip: Configure the JVM com.ibm.ws.runtime.component.disableMemoryLeakService custom property to permanently disable the service.

Procedure

Create or modify JVM custom properties to enable various aspects of the memory leak service, based on the table that follows. Read Java virtual machine custom properties to change the values of the JVM custom properties.

Table 1. com.ibm.ws.runtime.component.MemoryLeakConfig.detectAppCLLeaks
Information	Value
Name	com.ibm.ws.runtime.component.MemoryLeakConfig.detectAppCLLeaks
Description	When the server is shutting down or an application stops, WebSphere Application Server determines the classloaders that have leaked and issues warnings and other additional information that aids in debugging the memory leak. See also the Improved classloader leak detection PMR.
Default	false

Table 2. com.ibm.ws.runtime.component.MemoryLeakConfig.clearAppCLLeaks
Information	Value
Name	com.ibm.ws.runtime.component.MemoryLeakConfig.clearAppCLLeaks
Description	Enable proactive classloader leak mediation and fixing. When this property is set to true, WebSphere Application Server mediates on behalf of the application to remedy any classloader leaks that are detected.
Default	false

Table 3. com.ibm.ws.runtime.component.MemoryLeakConfig.preventJreMemoryLeaks
Information	Value
Name	com.ibm.ws.runtime.component.MemoryLeakConfig.preventJreMemoryLeaks
Description	Enable WebSphere Application Server to eliminate certain classes of memory leaks that are caused by the JRE loading singletons on the thread context classloader.
Default	true

Table 4. com.ibm.ws.runtime.component.MemoryLeakConfig.generateHeapDumps
Information	Value
Name	com.ibm.ws.runtime.component.MemoryLeakConfig.generateHeapDumps
Description	Set to true to cause a heapdump to be created when a memory leak is detected .
Default	true

Table 5. com.ibm.ws.runtime.component.MemoryLeakConfig.leakSweeperDelay
Information	Value
Name	com.ibm.ws.runtime.component.MemoryLeakConfig.leakSweeperDelay
Description	Delay after an application or module stops to check for classloader leaks.
Default	10000 (milliseconds)

Table 6. com.ibm.ws.runtime.component.MemoryLeakConfig.monitorSystemApps
Information	Value
Name	com.ibm.ws.runtime.component.MemoryLeakConfig.monitorSystemApps
Description	Set to true to watch for memory leaks on system applications that are shipped by IBM®, such as the administrative console.
Default	false

Attention: You can fine tune the leak action policy behavior using the following thread and timer leaks JVM custom properties. The ThreadLocal, thread, timer and static leak custom properties are applicable only if com.ibm.ws.runtime.component.MemoryLeakConfig.clearAppCLLeaks is set to true.

Table 7. com.ibm.ws.runtime.component.MemoryLeakConfig.clearReferencesInterruptThreads . Thread and timer leaks
Information	Value
Name	com.ibm.ws.runtime.component.MemoryLeakConfig.clearReferencesInterruptThreads
Description	Set to true for WebSphere Application Server to attempt to interrupt threads that are started by the web application. Interrupting threads is performed using the Thread.interrupt() method. There is a possibility that the target thread might not respond to the interrupt.
Default	true

Table 8. com.ibm.ws.runtime.component.MemoryLeakConfig.clearReferencesHttpClientKeepAliveThread . Thread and timer leaks
Information	Value
Name	com.ibm.ws.runtime.component.MemoryLeakConfig.clearReferencesHttpClientKeepAliveThread
Description	If an HttpClient keep-alive timer thread is not started by this web application and is still running, WebSphere Application Server changes the context class loader from the current classloader to its parent to prevent a memory leak. The keep-alive timer thread stops on its own when the keep-alive threads all die. However, on a busy system that might not happen for some time.
Default	true

Table 9. com.ibm.ws.runtime.component.MemoryLeakConfig.clearReferencesStopTimerThreads . Thread and timer leaks
Information	Value
Name	com.ibm.ws.runtime.component.MemoryLeakConfig.clearReferencesStopTimerThreads
Description	Set to true for WebSphere Application Server to stop any java.util.TimerThreads that are started by the web application.
Default	false

Table 10. com.ibm.ws.runtime.component.MemoryLeakConfig.jvmThreadGroupNames . Thread and timer leaks
Information	Value
Name	com.ibm.ws.runtime.component.MemoryLeakConfig.jvmThreadGroupNames
Description	List of ThreadGroup names to ignore when scanning for threads that are started by the web application that must be shut down. This list is delineated by underscores.
Default	system__RMI Runtime

Attention: The following static class variable leaks properties apply only if com.ibm.ws.runtime.component.MemoryLeakConfig.clearAppCLLeaks is set to true.

Table 11. com.ibm.ws.runtime.component.MemoryLeakConfig.clearReferencesStatic . Static class variable leaks
Information	Value
Name	com.ibm.ws.runtime.component.MemoryLeakConfig.clearReferencesStatic
Description	Set to true for WebSphere Application Server to attempt to make final fields null from loaded classes when a web application stops, as a work around for garbage collection bugs and application coding errors. Applications without memory leaks using recent JVMs should operate correctly when this option is set to false.
Default	false

Table 12. com.ibm.ws.runtime.component.MemoryLeakConfig.filterPrefixes . Static class variable leaks
Information	Value
Name	com.ibm.ws.runtime.component.MemoryLeakConfig.filterPrefixes
Description	Member attributes starting with these filters are not set to null when clearReferencesStatic is true.
Default	java javax com.ibm org sun com.sun. The list is delineated by spaces.

Attention: The following Threadlocal leaks properties apply only if com.ibm.ws.runtime.component.MemoryLeakConfig.clearAppCLLeaks is set to true.

Table 13. com.ibm.ws.runtime.component.MemoryLeakConfig.checkThreadLocalLeaks . Threadlocal leaks
Information	Value
Name	com.ibm.ws.runtime.component.MemoryLeakConfig.checkThreadLocalLeaks
Description	Determines if ThreadLocal leaks should be checked when an application stops.
Default	false

Table 14. com.ibm.ws.runtime.component.MemoryLeakConfig.clearReferencesThreadLocal . Threadlocal leaks
Information	Value
Name	com.ibm.ws.runtime.component.MemoryLeakConfig.clearReferencesThreadLocal
Description	Eliminate threadlocal leaks by renewing threads in the threadpool when an application stops. This property applies only to distributed platforms.
Default	true

Attention: The following properties apply only if clearReferencesThreadLocal is set to true.

Table 15. com.ibm.ws.runtime.component.MemoryLeakConfig.renewThreadPoolNames . Threadlocal leaks
Information	Value
Name	com.ibm.ws.runtime.component.MemoryLeakConfig.renewThreadPoolNames
Description	Threadpool names that WebSphere Application Server must renew when a threadlocal leak is detected.
Default	"WebContainer" list is delineated by spaces.

Table 16. com.ibm.ws.runtime.component.MemoryLeakConfig.threadPoolRenewalDelayFactor . Threadlocal leaks
Information	Value
Name	com.ibm.ws.runtime.component.MemoryLeakConfig.threadPoolRenewalDelayFactor
Description	Control the total amount of time to wait for thread pool to be renewed. The amount of time to wait for threadpool renewal = threadPoolRenewalDelayFactor * threadPool.getKeepAliveTime()
Default	10. For the web container threadpool, the renewal delay is (10 * 60000 ms) 6 minutes.

Table 17. com.ibm.ws.util.ThreadPool.DEFAULT_THREAD_RENEWAL_DELAY . Threadlocal leaks
Information	Value
Name	com.ibm.ws.util.ThreadPool.DEFAULT_THREAD_RENEWAL_DELAY
Description	Threads in the pool renew after an application stops. Use this custom property to avoid renewing all threads at the same time. This delay is observed between two threads being renewed.
Default	1000 (value is in ms). If the value is negative, threads are never renewed.

These JVM custom properties are persisted in the WebSphere Application Server configuration model in the server.xml file. The following code snippet displays the persisted leak policy configuration from the server_home/config/cells/nodes/servers/server.xml file of an unmanaged server:

<jvmEntries xmi:id="JavaVirtualMachine_1183122130078" verboseModeClass="true" verboseModeGarbageCollection="true" verboseModeJNI="false" 
runHProf="false" hprofArguments="" debugMode="false" debugArgs="-agentlib:jdwp=transport=dt_socket,server=y,suspend=n,address=7777" 
genericJvmArguments="-agentlib:getClasses -Xquickstart  -Xalwaysclassgc" executableJarFileName="" disableJIT="false">
	<systemProperties xmi:id="Property_1317048628648" name="com.ibm.ws.runtime.component.MemoryLeakConfig.detectAppCLLeaks"	value="true"	/>
	<systemProperties xmi:id="Property_1318975518491" name="com.ibm.ws.runtime.component.MemoryLeakConfig.clearAppCLLeaks"	value="true"	/>
	<systemProperties xmi:id="Property_1318955284241" name="com.ibm.ws.runtime.component.MemoryLeakConfig.generateSystemDumps"	value="false"	/>
	<systemProperties xmi:id="Property_1319119976147" name="com.ibm.ws.runtime.component.MemoryLeakConfig.generateHeapDumps"	value="true"	/>
	<systemProperties xmi:id="Property_1317048628649" name="com.ibm.ws.runtime.component.MemoryLeakConfig.monitorSystemApps"	value="false"	/>
</jvmEntries>

Click Apply.
Click OK.
Save the changes.
Make sure that a file synchronization is performed before restarting the servers.
Restart the Application Server for the changes to take effect.

Example

The Memory Leak policy for WebSphere Application Server can be configured and persisted using JVM custom properties as described in this example. At runtime the memory leak detection, prevention and policy configuration can be changed using the MemoryLeakConfig mbean.

Administration of the Memory leak policy can be carried out using the MemoryLeakAdmin mbean. The leak policy affects how the application server responds to a classloader memory leak when an application or when the server is stopped.

You can adjust the Memory leak policy settings by using the wsadmin scripting interface. These changes take effect immediately, but do not persist to the server configuration, and are lost when the server is restarted. The following script provides an example of how to configure and administer the memory leak policy using wsadmin jacl scripting :

# Scripting in JACL

# Get the object name of the MemoryLeak Configiration object  you want to change the values on
set leakConfig [$AdminControl completeObjectName "type=MemoryLeakConfig,*"]
WebSphere:cell=smitaNode03Cell,name=LeakConfig,type=MemoryLeakConfig,node=smitaNode03,process=server1

# Get the object name of the MemoryLeak Administration object  you want to issue operations
set leakAdmin [$AdminControl completeObjectName "type=MemoryLeakAdmin,*"]
WebSphere:cell=smitaNode03Cell,name=LeakAdmin,type=MemoryLeakAdmin,node=smitaNode03,process=server1

# Look at all the attributes of the MemoryLeakConfig mbean
wsadmin>$Help all $leakConfig
Name: WebSphere:cell=smitaNode03Cell,name=LeakConfig,type=MemoryLeakConfig,node=smitaNode03,process=server1
        Description: Information on the management interface of the MBean
        Class name: com.ibm.ws.runtime.component.MemoryLeakConfig

Attribute                       Type                            Access
JvmThreadGroupNames             java.lang.String                RW
FilterPrefixes                  java.lang.String                RW
RenewThreadPoolNames            java.lang.String                RW
DetectAppCLLeaks                boolean                         RW
ClearAppCLLeaks                 boolean                         RW
MonitorSystemApps               boolean                         RW
NoDumps                         boolean                         RW
GenerateHeapDumps               boolean                         RW
GenerateSystemDumps             boolean                         RW
ClearReferencesStatic           boolean                         RW
ClearReferencesInterruptThreads   boolean                       RW
ClearReferencesStopTimerThreads   boolean                       RW
ClearReferencesHttpClientKeepAliveThread  boolean               RW
ClearReferencesThreadLocal      boolean                         RW
LeakSweeperDelay                int                             RW
ThreadPoolRenewalDelayFactor    int                             RW
PreventJreMemoryLeaks           boolean                         RW
LeakConfiguration               java.lang.String                RO

Operation
Notifications
Constructors

# Print the current Memory Leak Policy configuration on the console 
wsadmin>$AdminControl getAttribute $leakConfig LeakConfiguration
MemoryLeakConfig [getClass()=class com.ibm.ws.runtime.component.MemoryLeakConfig, hashCode()=37266644
preventJreMemoryLeaks true
detectAppCLLeaks true
         monitorSystemApps false
         leakSweeperDelay 10000
clearAppCLLeaks true
         clearReferencesStopTimerThreads false
         clearReferencesHttpClientKeepAliveThread true
         clearReferencesInterruptThreads true
                  jvmThreadGroupNames [system, RMI Runtime]
         clearReferencesStatic true
                 filterPrefixes [java., javax., com.ibm., org., sun., com.sun]
         clearReferencesThreadLocal true
                  renewThreadPoolNames [WebContainer]
                  threadPoolRenewalDelayFactor 1
noDumps false
         generateHeapDumps true
         generateSystemDumps false

# Change the configuration
wsadmin>$AdminControl setAttribute $leakConfig ThreadPoolRenewalDelayFactor 10
wsadmin>$AdminControl setAttribute $leakConfig ClearReferencesStopTimerThreads true

# See the updated configuration
wsadmin>$AdminControl getAttribute $leakConfig LeakConfiguration
MemoryLeakConfig [getClass()=class com.ibm.ws.runtime.component.MemoryLeakConfig, hashCode()=37266644
preventJreMemoryLeaks true
detectAppCLLeaks true
         monitorSystemApps false
         leakSweeperDelay 10000
clearAppCLLeaks true
         clearReferencesStopTimerThreads true
         clearReferencesHttpClientKeepAliveThread true
         clearReferencesInterruptThreads true
                  jvmThreadGroupNames [system, RMI Runtime]
         clearReferencesStatic true
                 filterPrefixes [java., javax., com.ibm., org., sun., com.sun]
         clearReferencesThreadLocal true
                  renewThreadPoolNames [WebContainer]
                  threadPoolRenewalDelayFactor 10
noDumps false
         generateHeapDumps true
         generateSystemDumps false

# Look at all the operations of the MemoryLeakAdmin mbean
wsadmin>$Help all $leakAdmin
Name: WebSphere:cell=smitaNode03Cell,name=LeakAdmin,type=MemoryLeakAdmin,node=smitaNode03,process=server1
        Description: Information on the management interface of the MBean
        Class name: com.ibm.ws.runtime.component.MemoryLeakAdmin
Operation
java.lang.String findLeaks()
java.lang.String fixLeaks()
java.lang.String fixLeaks(java.lang.String)

# Find current classloader memory leaks
wsadmin>$AdminControl invoke $leakAdmin findLeaks
CWMML0028I: The following web applications were stopped (reloaded, undeployed), 
but their classes from previous runs are still loaded in memory, 
thus causing a memory leak.[[78577.075.724.NWALogging#NWALoggingEJB.jar]].

# Fix ALL current classloader memory leaks
wsadmin>$AdminControl  invoke $leakAdmin fixLeaks
CWMML0036I: Please watch the SystemOut log for results of the fix leak operation.

wsadmin>$AdminControl  invoke $leakAdmin fixLeaks {"78577.075.724.NWALogging#NWALoggingEJB.jar"}
CWMML0036I: Please watch the SystemOut log for results of the fix leak operation.