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A service you deployed on-premise grows memory over 72 hours. You have no shell access to the box. Diagnose it and say when it falls over.

Three different causes produce the same rising line, and resident memory alone cannot tell them apart: a leak climbed 25.2 MB an hour and fragmentation climbed 22.8. The gauge that separates them costs nothing and has to have been shipped before the incident.

Updated Aug 2026 · Grounded in real Forward Deployed Engineer interview loops and written to a senior-engineer editorial bar.

Three different causes produce the same rising line, and resident memory alone cannot tell them apart: a leak climbed 25.2 MB an hour and fragmentation climbed 22.8. The gauge that separates them costs nothing and has to have been shipped before the incident.

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UP NEXT ON YOUR JOURNEY
Next in this trackAn urgent fix has to reach a live customer instance that has no CI/CD and a strict zero-downtime change-control policy. Ship it.Next in this trackA customer wants AI coding agents working in their codebase. How do you assess whether it is ready, and what do you fix first?Next in this trackA customer wants AI code review on every PR. What does it catch, what does it miss, and how do you stop the team turning it off?
FEDITOR'S NOTE

This round is really about what the candidate shipped six months ago, not what they would do today. Anyone can describe attaching a profiler; the constraint is that they cannot. Strong answers reach for the two-gauge discriminator quickly, because resident memory alone cannot tell a leak from heap fragmentation and both look like the same rising line. The second thing to listen for is whether they give the customer a date. 'It is leaking' is not actionable. 'You have thirty nine hours' is.

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