feat(run_task): Add better_backpressure flag to avoid re-running function#536
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feat(run_task): Add better_backpressure flag to avoid re-running function#536
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…tion When RunTask experiences backpressure from next_step, the user function would run multiple times on the same message. This is because MessageRejected propagates up to the consumer, which retries the same message, causing the function to execute again. With better_backpressure=True, RunTask now stores the transformed message and retries submission in poll(), matching the Rust behavior. Ref STREAM-881 Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
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Address review feedback: - join() now flushes __message_carried_over before delegating to next_step - Parametrize existing tests on better_backpressure flag - Add specific tests for backpressure behavior and join() flushing Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
…sure=True Address review feedback: close() was closing next_step before join() could flush the carried-over message, causing AssertionError in downstream strategies. Now follows the pattern from RunTaskWithMultiprocessing: - close() only sets __closed flag - join() flushes pending message, then calls next_step.close(), then next_step.join() Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
markstory
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Apr 22, 2026
| cls, | ||
| function: Callable[[Message[TStrategyPayload]], TResult], | ||
| next_step: ProcessingStrategy[Union[FilteredPayload, TResult]], | ||
| better_backpressure: bool = False, |
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If this works well it seems like it could be the default going forward.
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i think this should be the intent, just didn't want to take the risk now
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Bumps arroyo to 2.39.0 and enables the new `better_backpressure=True` flag in the span buffer's RunTask. When the flusher applies backpressure, the current RunTask implementation re-raises `MessageRejected` and re-runs the user function on each retry attempt. This causes increased CPU load on Redis because `add-buffer.lua` executes multiple times per message. With `better_backpressure=True`, the function runs exactly once per message — transformed messages are stored on backpressure and retried in `poll()` instead. See getsentry/arroyo#536 for the arroyo change. Ref STREAM-881
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Summary
better_backpressure=Trueflag toRunTaskstrategypoll()instead of re-raisingMessageRejectedContext
The span buffer's flusher sometimes applies backpressure, causing increased CPU load on Redis. We suspect this is because
add-buffer.luais being executed multiple times per message when the currentRunTaskimplementation re-runs the function on each retry.With this fix (opt-in via
better_backpressure=True), the function runs exactly once per message, matching the Rust arroyo behavior.Ref STREAM-881
Test plan
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