This chapter introduces you into diagnostic tools that help you localize performance and memory issues.
CloverDX Server allows you to create a thread dump or a heap dump. The thread and heap dumps are useful for investigation of performance and memory issues.
In server GUI, go to→ → .
A heap dump is a content of the JVM process memory stored in a binary file. Creating a heap dump requires a Heap Memory Dump permission.
To download a heap dump of the Server Core, click the button under the Heap Dump section. Downloading the heap dump may take some time.
The Dump live objects only checkbox allows you to avoid dumping of objects awaiting garbage collection.
The heap dump of Worker can be created with jcmd command:
jcmd <pidOfWorker> GC.heap_dump <filename>
You should specify the file name with full path to avoid searching for the file
jcmd does not always create it in the working directory.
See details on jcmd.
To generate a heap dump on Out of Memory errors, add
-XX:+HeapDumpOnOutOfMemoryError to the
A dump file
java_pid.hprof will be generated when an Out of Memory error occurs.
The heap dump will be located in the working directory of the Worker's process
(same as the Server Core's working directory).
You can override the directory location with the
Important: the generated file can be large, its size is equal to the heap size.
The generated heap dump file can be investigated with tools like
You can use jvisualvm or jhat to view and analyze the heap dump.
A heap dump does not work on WebSphere. On WebSphere, you can create heap dumps using the administration console. For the instructions, see IBM Knowledge Center.
A thread dump is a list of existing JVM threads with their callstacks and held locking objects (if supported). It can be viewed in a text editor. Creating a thread dump requires a Heap Memory Dump permission.
To download the thread dump, click the Thread Dump section.button under the
The thread dump of Worker can be created with jcmd command:
jcmd <pidOfWorker> Thread.print
See details on jcmd.
Some memory and performance issues can be investigated with help of garbage collection logs.
To enable the logging of the Server Core, add
-verbose:gc -XX:+PrintGCTimeStamps -Xloggc:server_core_gc_log.txt to
Restart of the Server is required to reflect the configuration change.
To enable the garbage collection logging in Worker, add the flags
-verbose:gc -XX:+PrintGCTimeStamps -Xloggc:worker_gc_log.txt
to the Worker's JVM arguments field in the Setup GUI,
or the worker.jvmOptions property.
-Xloggc option sets the path for the detailed garbage collector log.
For the GC logging of Worker, use a different file name than for the Server.
You can analyze the log file with various tools, e.g. http://gceasy.io/.
Restart of Worker is required.
Another useful garbage collector flags are
For details on JVM flags, see Oracle's Java HotSpot VM Options.
Below are additional useful diagnostic tools:
To investigate usage of direct memory,
the worker.jvmOptions property.
The details on native memory usage can be displayed with
jcmd <pid> VM.native_memory summary.
For more information, see Native Memory Tracking tool.
Add the following options to the worker.jvmOptions property:
-Dcom.sun.management.jmxremote=true -Dcom.sun.management.jmxremote.port=8687 -Dcom.sun.management.jmxremote.authenticate=false -Dcom.sun.management.jmxremote.ssl=false -Djava.rmi.server.hostname=example.com
With the above options, you enable remote connection to JMX monitoring,
which provides a wide range of information about the running JVM, JNDI resources etc.
Change the value of
java.rmi.server.hostname to the hostname of your Server.