Celery

A misspelled Celery setting, a queue with no consumer, and LLEN 0 read as done: silent failures from a crawler's Redis migration, with checks that catch them.

On Celery's gevent pool, time_limit fires only at a cooperative switch and a bare except swallows it. Run CPU work on prefork and catch Exception instead.

self.retry(5) raises TypeError, timeout=5 waits 180 s, and except Exception catches Retry after it was sent. Use countdown= and re-raise TaskPredicate.

One flat OPTIONAL turns a three-hop SPARQL CONSTRUCT into a full dump. Also: rdflib ignores timeout= and hides 429s, and Celery chunks lose retries.