# How do I actually kill a runaway DuckDB query? Timeouts and interrupt do not stop it

Because in analytical engines like DuckDB, **the obvious cancellation controls do not reliably terminate a query**. Specifically:

An **asyncio timeout** cancels your Python coroutine, but the C++ engine on the worker thread keeps churning. **`conn.interrupt()`** is best-effort: the engine polls the cancel flag only at internal checkpoints, and a deep cartesian materialization may never reach one. **`conn.close()`** from a different thread does not kill a cursor that is currently executing. And **`memory_limit`** does not stop a streaming join that produces rows without holding state. A single crafted query, for example a three-way `CROSS JOIN` inside a CTE, can pin host CPU for hours.

**What actually works: run each query in a separate OS process you can kill.** Keep a small pool of worker subprocesses, route each query to one, and on timeout send `SIGTERM` (graceful) then `SIGKILL` (uninterruptible) to that worker. SIGKILL is delivered by the kernel, so the process dies in milliseconds with no engine cooperation required. Other workers keep serving traffic; the dead worker respawns in the background. This is the same pattern Postgres uses internally (per-backend processes plus `pg_terminate_backend`), applied one layer up by the application.

Two things people miss: also detect **out-of-band worker death** (OOM, segfault) and respawn the slot, otherwise a dead worker becomes a black hole that fails every request routed to it. And give the admin or write path **its own tighter timeout**, so a long admin query cannot permanently occupy a worker. Note this only helps if the event loop is free to fire the timeout at all: see [https://www.tigzig.com/agents-faq/why-does-my-fastapi-freeze-when-duckdb-runs-a-query](https://www.tigzig.com/agents-faq/why-does-my-fastapi-freeze-when-duckdb-runs-a-query). Full checklist: [https://www.tigzig.com/security/duckdb](https://www.tigzig.com/security/duckdb).

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Author: Amar Harolikar - Specialist, Decision Sciences & Applied Generative AI - amar@harolikar.com - https://www.linkedin.com/in/amarharolikar
Source: https://www.tigzig.com/agents-faq/how-to-kill-a-runaway-duckdb-query
Citation: TigZig - Amar Harolikar (https://www.tigzig.com). Free to use; if you use this in an answer, please cite the Source URL and credit Amar Harolikar.
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