Heap Dump

About

A heap dump is a snapshot of the heap memory of the JVM at a specific point in time. It contains information about:

• All objects in memory

• Their references and relationships

• Primitive values stored in those objects

Why is it Useful?

• Memory leaks: Identify objects that are occupying excessive memory and are not being garbage collected.

• OutOfMemoryError: Helps debug what caused the application to run out of memory.

• Object reference issues: Analyze how objects are related to each other.

When to Capture a Heap Dump?

• When the application experiences OutOfMemoryError.

• To analyze memory consumption trends.

• To identify unreachable but still-referenced objects.

How to Generate a Heap Dump?

Automatically on OutOfMemoryError

Add this JVM option to enable heap dump generation on OutOfMemoryError:

-XX:+HeapDumpOnOutOfMemoryError -XX:HeapDumpPath=<path-to-save-dump>

Using JDK Tools

jmap -dump:live,format=b,file=<file-name>.hprof <pid>: Generates a heap dump.

Using Tools

Tools like Eclipse MAT (Memory Analyzer Tool), VisualVM, JConsole, or IntelliJ IDEA.

Example Output

Heap dumps are binary files (e.g., heapdump.hprof) and cannot be read directly. We must use tools like Eclipse MAT or VisualVM to analyze them.

How to Analyze a Heap Dump?

• Look for retained memory: Identify objects that consume the most memory.

• Inspect object references: Trace how objects reference each other.

• Analyze garbage collection: Check for objects that should have been collected but are not.