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Troubleshooting in Production Environments - Clustering Guide 4.2.0 - WSO2 Documentation
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The following sections provide information on how to troubleshoot various problems that may arise for deployment in production environments.

Analyzing a stack trace

When your Java process starts to spin your CPU, you must immediately analyze the issue using the following two commands and obtain the invaluable information required to tackle the issue. This is done based on the process ID (pid).

  1. jstack <pid> > thread-dump.txt
  2. ps -C java -L -o pcpu,cpu,nice,state,cputime,pid,tid > thread-usage.txt

    Tip: OS X users can alternatively use the command ps M <PID> instead.

These commands provide you with the thread-dump.txt file and the thread-usage.txt file. After obtaining these two files, do the following.

  1. Find the thread ID (the one that belongs to the corresponding PID) that takes up the highest CPU usage by examining the thread-usage.txt file.

    %CPU CPU  NI S     TIME   PID   TID
      0.0   -   0 S 00:00:00  1519  1602
      0.0   -   0 S 00:00:00  1519  1603
     24.8   -   0 R 00:06:19  1519  1604
      2.4   -   0 S 00:00:37  1519  1605
      0.0   -   0 S 00:00:00  1519  1606

    In this example, the thread ID that takes up the highest CPU usage is 1604.

  2. Convert the decimal value (in this case 1604) to hexadecimal. You can use an online converter to do this. The hexadecimal value for 1604 is 644.
  3. Search the thread-dump.txt file for the hexadecimal obtained in order to identify the thread that spins. In this case, the hexadecimal value to search for is 644. The thread-dump.txt file should have that value as a thread ID of one thread.
  4. That thread usually has a stack trace, and that's the lead you need to find the issue. In this example, the stack trace of the thread that spins is as follows.

    "HTTPS-Sender I/O dispatcher-1" prio=10 tid=0x00007fb54c010000 nid=0x644 runnable [0x00007fb534e20000]
       java.lang.Thread.State: RUNNABLE
            at org.apache.http.impl.nio.reactor.IOSessionImpl.getEventMask(
            - locked <0x00000006cd91fef8> (a org.apache.http.impl.nio.reactor.IOSessionImpl)
            at org.apache.http.nio.reactor.ssl.SSLIOSession.updateEventMask(
            at org.apache.http.nio.reactor.ssl.SSLIOSession.inboundTransport(
            - locked <0x00000006cd471df8> (a org.apache.http.nio.reactor.ssl.SSLIOSession)
            at org.apache.http.impl.nio.reactor.AbstractIODispatch.inputReady(
            at org.apache.http.impl.nio.reactor.BaseIOReactor.readable(
            at org.apache.http.impl.nio.reactor.AbstractIOReactor.processEvent(
            at org.apache.http.impl.nio.reactor.AbstractIOReactor.processEvents(
            at org.apache.http.impl.nio.reactor.AbstractIOReactor.execute(
            at org.apache.http.impl.nio.reactor.BaseIOReactor.execute(
            at org.apache.http.impl.nio.reactor.AbstractMultiworkerIOReactor$

Capturing the state of the system

Carbondump is a tool used to collect all the necessary data from a running WSO2 product instance at the time of an error. The carbondump generates a ZIP archive with the collected data that helps to analyze the system and determine the problem that caused the error. Therefore, it is recommended that you run this tool as soon as an error occurs in the WSO2 product instance.

When using the tool, you have to provide the process ID (pid) of the product instance and the <PRODUCT_HOME> location, which is where your unzipped Carbon distribution files reside. The command takes the following format:

sh [-carbonHome path] [-pid of the carbon instance]

For example,

In Linux: sh -carbonHome /home/user/wso2carbon-3.0.0/ -pid 5151

In Windows: carbondump.bat -carbonHome c:\wso2carbon-3.0.0\ -pid 5151

The tool captures the following information about the system:

  • Operating system information** OS (kernel) version
    • Installed modules lists and their information
    • List of running tasks in the system
  • Memory information of the Java process** Java heap memory dump
    • Histogram of the heap
    • Objects waiting for finalization
    • Java heap summary. GC algo used, etc.
    • Statistics on permgen space of Java heap
  • Information about the running Carbon instance** Product name and version
    • Carbon framework version (This includes the patched version)
    • configuration files
    • log files
    • H2 database files
  • Thread dump
  • Checksum values of all the files found in the $CARBON_HOME
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