Generating HeapDump

Generating Heap dumps and Thread dumps Heap Dumps Heap dump is a text file which keeps record of all objects in the java heap. It contains the information like size and address of all objects, as well as the addresses of all objects that it references. Heap dump is nothing but a snap shot of our JVM’s Heap memory,contains all active java objects and their activities which object doing what and how much memory it is occupying. whenever OutOfMemoryException occurs Websphere application Server creates heap dump in profile's home directory. It is useful in situations, most notable for memory leak problems or memory allocation problems for exaple OutOfMemoryExceptions.

Automated heap dump generation (Server must start)

Set up for enabling heap dump:

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For V6.0 release: 1. To set the following Environment Entries from the administrative console: Select Servers > Application Servers >server_name> Java and Process Management > Process Definition > Environment Entries > New 2. Add the following Name/Value pairs: IBM_HEAPDUMP true IBM_HEAP_DUMP true IBM_HEAPDUMPDIR your_directory IBM_HEAPDUMP_OUTOFMEMORY true IBM_JAVADUMP_OUTOFMEMORY true 3. Make sure that you save changes to the master configuration

1.Click Servers > Application servers in the administrative console navigation tree.

2.Click server_name >Performance and Diagnostic Advisor Configuration.

3.Click the Runtime tab.

4.Select the Enable automatic heap dump collection check box.

5.Click OK. Heap Dump: Heap dump is a text file which keeps record of all objects in the java heap. It contains the information like size and address of all objects, as well as the addresses of all objects that it references. Before generating the heap dump, we need to enable the garbage collection to get only live objects information in dump. By Default, whenever OutOfMemoryException occurs Websphere application Server create heap dump in profile’s home directory. Heap dump is nothing but a snap shot of our JVM’s Heap memory, so here we can have all active java objects and their activities which object doing what and how much memory it is occupying.

websphere generate heap dump and java core dump with jython WAS_HOME\AppSrv01\bin\wsadmin.sh -lang jython wsadmin>ServerJVM = AdminControl.completeObjectName(‘type=JVM,process=server1,*’) wsadmin>AdminControl.invoke(ServerJVM,’dumpThreads’) wsadmin>AdminControl.invoke(ServerJVM,’generateHeapDump’)

Generating Heap dump Manually set jvm [$AdminControl completeObjectName type=JVM,process=server1,*] Where server1 is the name of application server for which we want heapdump. For generating heap dump: $AdminControl invoke $jvm generateHeapDump Generating Thread dump Manually set jvm [$AdminControl completeObjectName type=JVM,process=server1,*] Where server1 is the name of application server for which we want heapdump. For generating Thread dump:

$AdminControl invoke $jvm dumpThreads OR use kill -3 PID on unix/linux machines.

Thread Dump: When we trigger a thread dump on an application server, all active thread information will be dumped into file which is normally known as thread dump. In this dump file, we can get information about thread like active thread, hung thread, dead lock, runnable and inactive thread info. Command to generate thread dump: kill -3 PID_OF_SERVER When our application server reports the thread hung conditions in SystemOut.log file then we generate thread dump to analyze the reason behinds thread hungs. We are generally having thread hung situation when any threads coming to system becomes unresponded. When Websphere Application Server detects that a thread has been active longer than the time defined by the thread monitor threshold then it write below error code in SystemOut.log file: • WSVR0605W: Thread threadname has been active for hangtime and may be hung. There are totalthreads threads in total in the server that may be hung. Where: threadname is the name that appears in a JVM thread dump, hangtime gives an approximation of how long the thread has been active and totalthreads gives an overall assessment of the system threads. If the above thread gets released by itself then we get below entry in our log file: • WSVR0606W: Thread threadname was previously reported to be hung but has completed. It was active for approximately hangtime. There are totalthreads threads in total in the server that still may be hung.

Automatically

There are some conditions where a thread dump is created automatically for your Java Virtual Machine (JVM), such as when WebSphere Application Server is stopped by some means other than a normal stop server request Thread dumps can also be triggered by issuing a signal to the WebSphere Application Server process. For example, to produce a thread dump in a UNIX environment, you can run this command: kill -3 process_id

In order to manually generate a heapdump, you must first enable signal-based heapdumps by setting the IBM_HEAPDUMP=TRUE and IBM_NOSIGHANDLER=TRUE environmental variables.

What is the effect of changing max heap and min heap size of a jvm Max Heap Size: When you have established the maximum heap size that you need, you might want to set the minimum heap size to the same value; Using the same values is not usually a good idea, because it delays the start of garbage collection until the heap is full. The first time that the Garbage Collector runs, therefore, becomes a very expensive operation. Also, the heap is more likely to be fragmented and require a heap compaction. Again this is a very expensive operation. Min Heap Size: The recommendation is to start your application with the minimum heap size that it needs. When it starts up, the Garbage Collector will run often and, because the heap is small, it runs efficiently. Whats the max heap allowed by AIX Minimum heap size allowed AIX: 16 MB LINUX: 16MB WINDOWS: 16 MB Maximum heap size allowed AIX: Half the available memory with a minimum of 16 MB and a maximum of 512 MB LINUX: Half the available memory with a minimum of 16 MB and a maximum of 512 MB WINDOWS: Half the real (physical or RAM) memory with a minimum of 16 MB and a maximum of 2 GB What are the effects of large initial heap/max heap

The time between garbage collections will increase, but the garbage collection will take longer, which indirectly effects the turn-around-time of the applicaiton performance. (or) Because it delays the start of garbage collection until the heap is full. The first time that the Garbage Collector runs, therefore, becomes a very expensive operation. Also, the heap is more likely to be fragmented and require a heap compaction. Again this is a very expensive operation.

ANALYZING WEBSPHERE THREAD DUMP We can take thread dump on WAS using wsadmin tool in the following way. D:\IBM\WebSphere\AppServer\profiles\ProcessCommander\bin>wsadmin.bat WASX7209I: Connected to process “server1″ on node WKHANFXPNode02 using SOAP conn ector; The type of process is: UnManagedProcess WASX7029I: For help, enter: “$Help help” wsadmin>set jvm [$AdminControl completeObjectName type=JVM,process=server1,*] WebSphere:name=JVM,process=server1,platform=proxy,node=WKHANFXPNode02,j2eeType=J VM,J2EEServer=server1,version=6.1.0.0,type=JVM,mbeanIdentifier=JVM,cell=WKHANFXP Node01Cell,spec=1.0 wsadmin>$AdminControl invoke $jvm dumpThreads This will create a java core file in the following directory D:\IBM\WebSphere\AppServer\profiles\ProcessCommander javacore.20110511.174141.9628.txt We need to download IBM Thread Dump Analyzer from here Start the tool using the following command E:\tools\jca412>java -Xmx515m -jar jca412.jar Open the thread dump from

File > Open Thread Dumps Then click on Analysis > Thread Details.

This will give you details of all the threads.