DebugSeniorBackendAuto-graded

Plug two memory leaks in an event bus

Tests whether someone can find slow resource growth that only becomes visible after a service runs for hours.A notifications worker built on an in-process event bus runs fine for hours, then its memory climbs until the OOM killer restarts it. It only happens in production under sustained churn, and nobody can reproduce it locally. Two structures inside EventBus grow without bound as the workload flows through them. Find both, bound their growth, and do not break the behaviour that depends on them.

35 min

python

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You're done when

Delivery still reaches all current subscribers.
Unsubscribing genuinely stops delivery and releases what was held for that subscriber.
Event deduplication still works correctly.
The subscriber structure stays bounded rather than growing with churn.
The deduplication structure stays bounded too.
Memory stays bounded as the volume of events processed grows.

What it measures

Debugging and profilingLocating unbounded growth in a system that behaves perfectly until it has been running for hours.

PythonUnderstanding what keeps an object alive, and which structures quietly retain references forever.

Fixing without regressingBounding growth while preserving delivery, unsubscription and dedup — the behaviours those structures existed to provide.

Your environment

Terminal + editorA full shell in the browser

Claude CodePre-authenticated, no key setup

Isolated microVMYours alone, wiped afterwards

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35 min

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