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Using WebLogic Server Clusters

# Troubleshooting Common Problems

This chapter provides guidelines on how to prevent cluster problems or troubleshoot them if they do occur.

# Before You Start the Cluster

You can do a number of things to help prevent problems before you boot the cluster.

## Check for a Cluster License

Your WebLogic Server license must include the clustering feature. If you try to start a cluster without a clustering license, you will see the error message Unable to find a license for clustering.

## Check the Server Version Numbers

All Managed Servers in a cluster and the cluster's Administration Server should run under the same version of WebLogic Server. The major and minor version numbers (e.g 6.1), service packs, and attached patch levels should be same across the cluster.

## Check the Multicast Address

A problem with the multicast address is one of the most common reasons a cluster does not start or a server fails to join a cluster.

A multicast address is required for each cluster. The multicast address can be an IP number between 224.0.0.0 and 239.255.255.255, or a host name with an IP address within that range.

You can check a cluster's multicast address and port on its Configuration-->Multicast tab in the Administration Console.

For each cluster on a network, the combination of multicast address and port must be unique. If two clusters on a network use the same multicast address, they should use different ports. If the clusters use different multicast addresses, they can use the same port or accept the default port, 7001.

Before booting the cluster, make sure the cluster's multicast address and port are correct and do not conflict with the multicast address and port of any other clusters on the network.

The errors you are most likely to see if the multicast address is bad are:

`Unable to create a multicast socket for clustering`

`Multicast socket send error`

`Multicast socket receive error`

## Check the CLASSPATH Value

Make sure the value of `CLASSPATH` is the same on all managed servers in the cluster. `CLASSPATH` is set by the `setEnv` script, which you run before you run `startManagedWebLogic` to start the managed servers.

By default, `setEnv` sets this value for `CLASSPATH` (as represented on Windows systems):

>     set WL_HOME=C:\bea\weblogic700
>     set JAVA_HOME=C:\bea\jdk131
>     .
>     .
>     set CLASSPATH=%JAVA_HOME%\lib\tools.jar;
>     	%WL_HOME%\server\lib\weblogic_sp.jar;
>     	%WL_HOME%\server\lib\weblogic.jar;
>     	%CLASSPATH%

If you change the value of `CLASSPATH` on one managed server, or change how `setEnv` sets `CLASSPATH`, you must change it on all managed servers in the cluster.

## Check the Thread Count

Each server instance in the cluster has a default execute queue, configured with a fixed number of execute threads. To view the thread count for the default execute queue, choose the Configure Execute Queue command on the Advanced Options portion of the Configuration> General tab for the server. The default thread count for the default queue is 15, and the minimum value is 5. If the value of Thread Count is below 5, change it to a higher value so that the Managed Server does not hang on startup.

# After You Start the Cluster

This section describes first troubleshooting steps to perform if you have problems trying to start a cluster.

## Check Your Commands

If the cluster fails to start, or a server fails to join the cluster, the first step is to check any commands you have entered, such as `startManagedWebLogic` or a `java` interpreter command, for errors and misspellings.

## Generate a Log File

Before contacting BEA Technical Support for help with cluster-related problems, collect diagnostic information. The most important information is a log file with multiple thread dumps from a Managed Server. The log file is especially important for diagnosing cluster freezes and deadlocks.

Remember: a log file that contains multiple thread dumps is a prerequisite for diagnosing your problem.

1. Stop the server.
2. Remove or back up any log files you currently have. You should create a new log file each time you boot a server, rather than appending to an existing log file.
3. Start the server with this command, which turns on verbose garbage collection and redirects both the standard error and standard output to a log file:

>     % java -ms64m -mx64m -verbose:gc -classpath $CLASSPATH
>     	-Dweblogic.domain=mydomain -Dweblogic.Name=clusterServer1
>     	-Djava.security.policy==$WL_HOME/lib/weblogic.policy
>     	-Dweblogic.admin.host=192.168.0.101:7001
>     	 weblogic.Server >> logfile.txt

Redirecting both standard error and standard output places thread dump information in the proper context with server informational and error messages and provides a more useful log.

4. Continue running the cluster until you have reproduced the problem.
5. If a server hangs, use `kill -3` or `<Ctrl>-<Break>` to create the necessary thread dumps to diagnose your problem. Make sure to do this several times on each server, spaced about 5-10 seconds apart, to help diagnose deadlocks.

Note: If you are running the JRockit JVM under Linux, see Getting a JRockit Thread Dump Under Linux.

1. Compress the log file using a Unix utility:

>     % tar czf logfile.tar logfile.txt

- or zip it using a Windows utility.

2. Attach the compressed log file to an e-mail to your BEA Technical Support representative. Do not cut and paste the log file into the body of an e-mail.
3. If the compressed log file is too large, you can use the BEA Customer Support FTP site.

### Getting a JRockit Thread Dump Under Linux

If you use the JRockit JVM under Linux, use one of the following methods to generate a thread dump.

- Use the `weblogic.admin THREAD_DUMP` command. For instructions and limitations, see THREAD_DUMP in WebLogic Server Command Reference.
- If the JVM's management server is enabled (by starting the JVM with the -`Xmanagement` option), you can generate a thread dump using the JRockit Management Console.
- Use `Kill -3` `PID`, where `PID` is the root of the process tree.

To obtain the root PID, perform a:

`ps -efHl | grep 'java' **. **`

using a `grep` argument that is a string that will be found in the process stack that matches the server startup command. The first PID reported will be the root process, assuming that the `ps` command has not been piped to another routine.

Under Linux, each execute thread appears as a separate process under the Linux process stack. To use Kill -3 on Linux you supply must match PID of the main WebLogic execute thread, otherwise no thread dump will be produced.

## Check Garbage Collection

If you are experiencing cluster problems, you should also check the garbage collection on the managed servers. If garbage collection is taking too long, the servers will not be able to make the frequent heartbeat signals that tell the other cluster members they are running and available.

If garbage collection (either first or second generation) is taking 10 or more seconds, you need to tune heap allocation (the `msmx` parameter) on your system.

## Run utils.MulticastTest

You can verify that multicast is working by running `utils.MulticastTest` from one of the managed servers. See Using the WebLogic Server Java Utilities in WebLogic Server Command Reference.