Java Heap Dumps

As name suggest, Heap dumps are only for java processes.

Commands to take heap dumps:

• jmap -dump:live,format=b,file=heap.process_name.prof <PID>
• jmap -dump:live,format=b,file=/home/Dumps/heap.process_name.prof <PID> 

Thread Analysis:

For analysis, we can use Java VisualVM and Eclipse Memory Analyzer

Heap Dump Parameter:

-Xms          set initial Java heap size in m,g or M,G (and not MB or GB)
-Xmx          set maximum Java heap size in m,g or M,G (and not MB or GB)

Garbage Collection:
In Java, there is object life cycle as below:

• Object creation
• Object in use
• Object destruction

We need to clean object to release memory else we will have heap memory reaching 100%. Garbage collection is a way in Java which happens automatically and below are the available algorithm:

• Mark and sweep:

• Concurrent mark sweep (CMS) garbage collection:

To use CMS GC, use below JVM argument:
-XX:+UseConcMarkSweepGC

• Serial garbage collection:

To use Serial GC, use below JVM argument:
-XX:+UseSerialGC

• Parallel garbage collection:

To use parallel GC, use below JVM argument:
-XX:+UseParallelGC

• G1 garbage collection:

If you want to use in Java 7 or Java 8 machines, use JVM argument as below:
-XX:+UseG1GC