fix/deployment-concurrency-slot-starvation - Branch - PrefectHQ/prefect

Fix deployment concurrency slot starvation bug

#19824Closed

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fix/deployment-concurrency-slot-starvation

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a88dcb7

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3d56c1a

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Benchmarks

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bench_task_decorator

benches/bench_tasks.py

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bench_import_prefect_flow

benches/bench_import.py

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benches/bench_flows.py

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benches/bench_flows.py

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benches/bench_tasks.py

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bench_import_prefect

benches/bench_import.py

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bench_flow_decorator

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Commits

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main

3d56c1a

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Fix deployment concurrency slot starvation bug When a flow run is rejected to AwaitingConcurrencySlot state, its scheduled_time was set to now + 30 seconds (concurrency_slot_wait_seconds default). However, workers poll for runs with scheduled_before = now + 10 seconds (prefetch_seconds default). This mismatch caused runs to be invisible to workers for 20+ seconds, and if the slot was still unavailable when finally polled, they'd be rescheduled another 30 seconds out - creating indefinite starvation. Fix: Reduce concurrency_slot_wait_seconds default from 30s to 5s, ensuring runs become visible within the worker's prefetch window. Adds regression tests: - test_enqueued_runs_acquire_slots_after_release - test_enqueued_runs_visible_in_worker_polling_query - test_awaiting_concurrency_slot_visible_within_worker_prefetch_window 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

a88dcb7

17 hours ago

by zzstoatzz

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