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.
-
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.