jmap

About

jmap is a JDK utility used to generate heap dumps or analyze memory usage in a Java application. A heap dump is a snapshot of the JVM's memory, including all objects and references at a specific point in time. It is essential for diagnosing memory leaks, OutOfMemoryError, or high memory usage.

Key Use Cases

• Diagnosing memory leaks by analyzing objects and their references.

• Understanding the distribution of objects in memory.

• Debugging OutOfMemoryError issues.

Steps to Use jmap on Mac

1. Find the Process ID (PID):

• Use the jps command to locate your Spring Boot app’s PID:

jps

Output example:

Start the Java Application (here it is sample-print-service maven springboot application)

jps command output is below

Here, 83322 is the PID of our Springboot app.

2. Capture a Heap Dump:

• Run the following jmap command to generate a heap dump:

jmap -dump:format=b,file=heap-dump.hprof 83322

• format=b: Specifies the binary format for the dump file.

• file=heap-dump.hprof: Specifies the file name for the heap dump.

• The heap-dump.hprof file will be saved in the current directory.

3. Analyze the Heap Dump:

• Use tools like Eclipse MAT (Memory Analyzer Tool) or VisualVM to open and analyze the heap-dump.hprof file.

  • Look for objects with high retention, large collections, or unreferenced objects.

  • Detect memory leaks by identifying objects that cannot be garbage collected.