How Can JHat Help Identify and Analyze Java Memory Leaks?

Identifying Memory Leaks in Java Using JHat

Memory leaks in Java can be a frustrating problem to diagnose, but understanding how to use JHat can help you pinpoint the root causes. Despite JHat's limited graphical capabilities, it offers a cost-effective alternative to paid tools.

To find a memory leak in Java using JHat, follow these steps:

1. Establish a Baseline Snapshot:

   • Start the application and allow it to stabilize.
   • Run the suspected operation several times to initiate any necessary initialization.
   • Perform a Garbage Collection and capture a memory snapshot (accessible via JHat).

2. Execute the Suspected Operation:

   • Run the operation again to trigger the memory leak.
   • Allow the operation to complete multiple times to ensure significant memory consumption.

3. Compare Memory Snapshots:

   • Perform a Garbage Collection again and capture another memory snapshot.
   • Use JHat to compare the two snapshots and identify the differences.

4. Analyze the Differences:

   • Focus on objects with large positive differences in size.
   • Determine which objects are potentially holding onto references and causing the memory leak.

Tips for Using JHat:

• If the memory leak is caused by large maps, consider searching for "[java.util.HashMap$Entry]".
• Explore the object trees to find general roots of large objects that may be contributing to the leak.

Troubleshooting:

• If possible, avoid modifying the code to add logging, as this can introduce artificial memory usage.
• If the suspected operation is long-running, consider capturing snapshots at regular intervals to reduce the risk of missing the leak.

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