Memory Leak

Overview and Tools

AGENDA

Overview of Java Heap What is a Memory Leak Symptoms of Memory Leaks How to troubleshoot Tools Best Practices to avoid/detect Memory Leak Q & A

Overview of Java Heap

Java Heap can be categorized into three generations: - Young, Tenured and Permanent.

Young generation has Eden Space and two survivor spaces. All newly created objects are kept in Eden Space and moved to one of the survivor space after it survives few gc’s. From one survivor space it moves to another. At an instant one of the survivor space is completely free. From the survivor space, objects are moved to the tenured generations.

Permanent holds class data, such as describing classes and methods.

What is a Memory Leak

Memory leak is when objects are not removed from the heap even when they are not required.

This can be due to application code, application server code, database driver or third party jar files.

Symptoms of Memory Leak

Very frequent FULL GC Lesser memory is reclaimed on each Full GC Available free heap keeps on decreasing over time Response time decreases

How to troubleshoot

Gather GC Information by adding the following JVM flags

-Xloggc=filename verbose:gc -XX:+PrintGCTimeStamps -XX:+PrintGCDetails

Tools

Use GC Viewer to analyze the gc log

Jprofiler

Memory profiling (Class Monitor, Allocation Monitor) Heap walker (Show all Class instances,

Allocations,References) CPU profiling (Invocation Tree, Hot spots, Method

Graph,CPU statistics)

Visual VM

Best Practices to avoid or detect Memory Leak

Keep a watch on heap usage and use alert mechanisms.

Free up unnecessary objects. Close all connections in the finally block Don’t keep too much data in session.

Q&A