Heap Dump

A heap dump is a snapshot of all the objects in a Java process's heap memory at a specific point in time, written to a file. It captures every object, its class, its size, and the references connecting objects to each other.

Heap dumps are an essential tool for diagnosing memory-related problems. If your application is running out of memory, growing slowly over time (a memory leak), or consuming far more RAM than expected, a heap dump lets you see exactly what is occupying the heap and trace why objects are being retained.

Common ways to capture a heap dump include the jmap command-line tool, the -XX:+HeapDumpOnOutOfMemoryError JVM flag (which writes a dump automatically when the application crashes with an OutOfMemoryError), and JDK Mission Control. The resulting file — usually with a .hprof extension — can be analysed with tools such as Eclipse MAT (Memory Analyzer Tool) or VisualVM.

A heap dump is closely related to a thread dump, but while a thread dump captures the state of running threads, a heap dump captures the state of memory.