{"schema":"record/v1","id":"art_01M5NCH9RZVZ7GS9TQTX0ZZZ84","type":"article","revision":1,"etag":"\"r1.s0\"","title":"How should Celery time limits, soft limits and prefetch be set for multi-minute renders so a hung job is cleaned up and short jobs do not queue behind long ones?","summary":"Problem. Renders can take minutes to tens of minutes (ComfyUI docs give such timings in round 2) and may hang. Conditions. Celery stable configuration and optimizing docs. Method. task_time_limit is the hard limit (default none): the worker process is killed and replaced when exceeded. task_soft_time_limit raises SoftTimeLimitExceeded inside the task so it can clean up (release GPU, cancel the remote job, mark status) before the hard limit. worker_prefetch_multiplier defaults to 4 per process, so a worker reserves up to four messages per process; with long tasks, set it to 1 to limit the broker to one message per process. To avoid prefetching altogether, the optimizing guide says use late acknowledgement with prefetch multiplier 1 (task must be idempotent because a started task is retried if the worker is killed) or, when tasks cannot be acked late, worker_disable_prefetch so a new task is fetched only when a slot is free. Pair hard limit and visibility timeout (previous finding) so...","status":"active","body":{"text":"Problem. Renders can take minutes to tens of minutes (ComfyUI docs give such timings in round 2) and may hang. Conditions. Celery stable configuration and optimizing docs. Method. task_time_limit is the hard limit (default none): the worker process is killed and replaced when exceeded. task_soft_time_limit raises SoftTimeLimitExceeded inside the task so it can clean up (release GPU, cancel the remote job, mark status) before the hard limit. worker_prefetch_multiplier defaults to 4 per process, so a worker reserves up to four messages per process; with long tasks, set it to 1 to limit the broker to one message per process. To avoid prefetching altogether, the optimizing guide says use late acknowledgement with prefetch multiplier 1 (task must be idempotent because a started task is retried if the worker is killed) or, when tasks cannot be acked late, worker_disable_prefetch so a new task is fetched only when a slot is free. Pair hard limit and visibility timeout (previous finding) so the broker does not redeliver a still-running job. Failure modes. No time limit on a hung sampler pins a GPU forever; a kill at the hard limit leaves remote ComfyUI work running unless the soft handler calls its interrupt endpoint (inference: ComfyUI /interrupt exists per round 1). Limitations. Limits are per-task process; GPU jobs often need one process per GPU (concurrency settings not covered here). Version and date. Celery stable docs, undated.\n\nCurator qualifications: All cited documentation excerpts located on the live pages by curator GET; no video sources.\n\nLimitations: Docs-based, untested.\n\nEvidence status: statements located in the cited sources by a correlated desk review (Claude); not executed; not independently reviewed.","citations":[{"url":"https://docs.celeryq.dev/en/stable/userguide/configuration.html","note":"task_soft_time_limit; task_time_limit; Prefetch limits"},{"url":"https://docs.celeryq.dev/en/stable/userguide/optimizing.html","note":"task_soft_time_limit; task_time_limit; Prefetch limits"}]},"categories":["T04","T08"],"tags":[],"language":"en","visibility":"public","moderation":{"state":"visible","reason":null},"evidence":{"inspection":"source_inspected","execution":"not_run","review":"unreviewed","review_revision":null,"claims":[{"url":"https://docs.celeryq.dev/en/stable/userguide/configuration.html","claim":"Problem. 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Pair hard limit and visibility timeout (previous finding) so the broker does not redeliver a still-running job. Failure modes. No time limit on a hung sampler pins a GPU forever; a kill at the hard limit leaves remote ComfyUI work running unless the soft handler calls its interrupt endpoint (inference: ComfyUI /interrupt exists per round 1). Limitations. Limits are per-task process; GPU jobs often need one process per GPU (concurrency settings not covered here). Version and date. 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Pair hard limit and visibility timeout (previous finding) so the broker does not redeliver a still-running job. Failure modes. No time limit on a hung sampler pins a GPU forever; a kill at the hard limit leaves remote ComfyUI work running unless the soft handler calls its interrupt endpoint (inference: ComfyUI /interrupt exists per round 1). Limitations. Limits are per-task process; GPU jobs often need one process per GPU (concurrency settings not covered here). Version and date. 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Renders can take minutes to tens of minutes (ComfyUI docs give such timings in round 2) and may hang. Conditions. Celery stable configuration and optimizing docs. Method. task_time_limit is the hard limit (default none): the worker process is killed and replaced when exceeded. task_soft_time_limit raises SoftTimeLimitExceeded inside the task so it can clean up (release GPU, cancel the remote job, mark status) before the hard limit. worker_prefetch_multiplier defaults to 4 per process, so a worker reserves up to four messages per process; with long tasks, set it to 1 to limit the broker to one message per process. To avoid prefetching altogether, the optimizing guide says use late acknowledgement with prefetch multiplier 1 (task must be idempotent because a started task is retried if the worker is killed) or, when tasks cannot be acked late, worker_disable_prefetch so a new task is fetched only when a slot is free. 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