When do you take a thread dump versus a heap dump on a stuck Spring Boot box?
PICTURE THIS: HOW JAVA RUNS
Simple meaning
Thread dump if requests hang, CPU is high on a few threads, or you suspect deadlock: you see stack traces and lock owners.
WHY — JVM instead of guessing?
Why interviewers care about JVM:
contrast on JVM, not two memorised paragraphs.
the developer, then one case where picking wrong hurts.
Name the idea, why it exists, then one short example.
End with when you use it and one common pitfall.
STEPS — What happens step by step?
Before you speak the answer, walk the interviewer through these steps:
- 1Thread dump if requests
hang, CPU is high on a few threads, or you suspect deadlock: you see stack traces and lock owners.
- 2Heap dump if memory
grows or you see frequent Full GCs: you inspect retained size.
- 3Taking a huge heap
dump on a dying node can freeze it, so prefer a canary instance when you can.
- 4Give an example
One tiny concrete case you can say aloud.
- 5Common mistake
What juniors usually get wrong.
- 6Close
When you pick this over the alternative.
EXAMPLE — See it in action
Here's a short line you can speak, broken into clear beats:
Note: Adapt this scaffold to your own project — keep it under 60–90 seconds.
Key takeaway
Thread dump if requests hang, CPU is high on a few threads, or you suspect deadlock: you see stack traces and lock owners. Heap dump if memory grows or you see frequent Full GCs: you inspect retained size.