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WebSphere Application Server Java Dumps

Description and problem determination

Example 2 – You can see the Compiled Code and Inlined Compiled Code references where the line number in a typical stack trace is observed. Threads have states, as shown in Example 1. Most threads will indicate either an R or a CW state. The following is a list of states and a brief description of each:
  • R – A Runnable Thread that can run or is running. On platforms such as AIX and Linux, you can see which thread is actually running via the XHPI - Current Thread Details.
  • CW – A Conditional Wait Thread is waiting on a condition variable, typically a certain condition to occur. For example, a thread may be waiting for a resource to become available.
  • MW – A Monitor Wait Thread is waiting on a monitor lock.
  • S – A Suspended Thread is suspended.

Looking into Monitors – LK Dump Routine
The following table shows how the LK Dump routine is broken down into five subsections:

  • Monitor Pool Info provides basic monitor information, such as, the current total number of monitors, and so on.
  • Monitor Pool Dump lists the monitors that exist in the JVM at the time of the Java dump along with the threads waiting for that particular monitor and the owner of each monitor. Monitors can be owned or not owned as indicated in the file. You can use this section to identify any problems, such as, too many threads waiting on a monitor.
  • JVM System Monitor Dump is similar to the monitor pool dump except that instead of listing any monitor, it lists all of the system monitors on the JVM for which the Java dump was captured.
  • Java Object Monitor Dump is the same as the monitor pool dump except that additional JVM internal information is provided.
  • Thread Identifiers provide an association between the XM dump routine and the monitor pool dump. You can use this section as a pointer to the location of the problem identified in the monitor pool dump.

Looking into Classloaders – CL Dump Routine
The CL dump routine shows the list of class loaders and their corresponding classes. The respective address for each class and class loader is also shown in this section of the Java dump. The type for each class loader is shown to the left of the name of the class loader indicating if the class loader is primordial, extension, shareable, middleware, system, or trusted.

WebSphere Application Server Java Dumps
There are several types of threads that appear when you generate a Java dump in a WebSphere Application Server. The following list contains the types of threads that reside in most WebSphere Application Server Java dumps:
  • Server Socket threads – Server Socket threads listen for the incoming request in the Web container component of WebSphere Application Server. When the threads get a request they delegate the work to the Servlet Engine Transport thread. For example, the Server Socket thread listens to incoming Web requests (port 9080, by default) and delegates the request to the Servlet Engine Transport threads. When there’s a backlog of connections, the Server Socket threads operate like the Apache Web server, which means that there’ll be a maximum of 511 backlog connections supported. When there are more than 511 clients in addition to the Servlet Engine Transport thread maximum, the next client will be refused service.
3XMTHREADINFO “ServerSocket[addr=,port=0,localport=9085]” (TID:0x10628F00,
sys_thread_t:0x4D87A80, state:R, native ID:0x9C4) 
4XESTACKTRACE at java.net.PlainSocketImpl.
  socketAccept(Native Method)
4XESTACKTRACE at java.net.PlainSocketImpl.
  accept(PlainSocketImpl.java(Compiled Code))
4XESTACKTRACE at java.net.ServerSocket.
  implAccept(ServerSocket.java(Compiled Code))
4XESTACKTRACE at java.net.ServerSocket.
  accept(ServerSocket.java(Compiled Code))
4XESTACKTRACE at com.ibm.ws.http.HttpTransport.
4XESTACKTRACE at java.lang.Thread.run(Thread.java:568)
Example 3 – This example shows the Server Socket thread listening to port 9085 on an IBM V1.4.1 JVM and accepting a connection.
  • Servlet Engine Transport threads – WebSphere Application Server maintains the Servlet Engine Transport threads in a thread pool. These threads execute the service methods of the servlets. Depending on the settings for the thread pool and the number of new incoming requests, you can create transport threads or use ones from the thread pool. The number of transport threads occupied by requests coincides with the number of unique clients connected to the Web container. If you enable the KeepAlive parameter, the connection persists as long as you specify through this parameter and the Servlet Engine Transport thread will be reserved for a particular user during this time. In other words, a blocking Input/Output (I/O) operation is performed in the Servlet Engine Transport thread.
3XMTHREADINFO “Servlet.Engine.Transports : 0” 
  (TID:0x10631CC8, sys_thread_t:0x4E397A8, state:R,
native ID:0xEF4) prio=5
4XESTACKTRACE at java.net.SocketInputStream.
  socketRead0(Native Method)
4XESTACKTRACE at java.net.SocketInputStream.
  read(SocketInputStream.java(Compiled Code))
4XESTACKTRACE at com.ibm.ws.io.Stream.read(Stream.
4XESTACKTRACE at com.ibm.ws.io.ReadStream.
  readBuffer(ReadStream.java(Compiled Code))
4XESTACKTRACE at com.ibm.ws.io.ReadStream.
  read(ReadStream.java(Compiled Code))
4XESTACKTRACE at com.ibm.ws.http.HttpRequest.
  readRequestLine(HttpRequest.java(Compiled Code))
4XESTACKTRACE at com.ibm.ws.http.HttpRequest.
4XESTACKTRACE at com.ibm.ws.http.HttpConnection.
4XESTACKTRACE at com.ibm.ws.http.HttpConnection.
4XESTACKTRACE at com.ibm.ws.util.ThreadPool$Worker.
  run(ThreadPool.java(Compiled Code))

More Stories By Dipak Patel

Dipak M. Patel is a Senior IT specialist for IBM Software Services Performance Technology group. He has been focused on solving complex performance related problems involving WebSphere Application Server and Business Integration solutions. Dipak has a bachelors degree in Electrical Engineering and a masters degree in Computer Science from the University of Akron.

More Stories By Michel Betancourt

Michel Betancourt has been focused on WebSphere Application Server problem determination while part of IBM’s World Wide WebSphere Solutions War Room team. He was graduated from Florida International University in 2001 with a bachelor’s in computer engineering.

More Stories By Lorrie Barber

Lorrie M. Barber has been in WebSphere Application Server information development since 2001 focusing on system administration. She has a BS in computer information systems from the University of North Carolina at Wilmington and an MS in technical communication from North Carolina State University.

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