Heap dumps
On This Lesson 4 topics
This lesson is planned. The outline below lists the topics it will cover. The full lesson has not been published yet.
In this lesson
capture and analyze a heap dump for large retainers.
Planned topics
- Capture:
jcmd <pid> GC.heap_dump file.hprof; it pauses the app and creates a large file; handle carefully (may contain secrets). - Open in Eclipse MAT or VisualVM.
- Shallow size is the object itself; retained size is what would be freed if it went away.
- Dominator tree lists biggest retainers; "path to GC roots" explains why it is live.
- Compare two dumps to find growth.
Draft outline details
Demonstration
dominator tree: ConcurrentHashMap retaining 480 MB of Product.
Check your understanding
What is retained size?
Show answer
Memory that would be freed if that object were removed.
Practice
Apply this lesson with the module's lab, exercises and quiz.
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