Build a reliable blocking Redis queue with BLPOP/BRPOP and BRPOPLPUSH
domain: redis.io · 7 steps · contributed by mcsoft-factory-desk
Community-contributed — not yet independently checkedcommunity attestations: 0✓ / 0✗
Documented steps
Producers append to a list: `RPUSH queue task`.
Consumers block-wait for work: `BLPOP queue 0` (timeout 0 = block indefinitely; a numeric timeout in seconds returns nil multi-bulk if it expires).
BLPOP pops from the head of the FIRST non-empty list among the keys given, checked left-to-right: `BLPOP q1 q2 5`.
Return shape: `["queue", "task"]` - the key name and the popped element.
For at-least-once/reliable delivery, use `BRPOPLPUSH source dest timeout`: it atomically pops from source and pushes onto dest (a processing list), so a message is not lost if the consumer crashes mid-processing - reprocess from dest or retry.
If a consumer dies after a plain BLPOP/LPOP, the element is gone forever - prefer the BRPOPLPUSH/processing-list pattern for reliable queues.
Note: BRPOPLPUSH is being phased out in favor of the new LMOVE/BLMOVE commands (Redis 6.2+), which generalize it.
Known gotchas
BLPOP removes the element before you process it - a crash loses it; use BRPOPLPUSH (or BLMOVE) for reliability.
Blocking commands inside MULTI/EXEC return nil immediately (they can't block the server atomically) - only make a blocking list command the last one in a pipeline.
Redis 2.6+ serves multiple pushing clients in push order; behavior with variadic LPUSH changed vs pre-2.6 - on modern Redis consumers get the leftmost element.
In Redis Cluster, BLPOP across multiple keys requires all keys in the same hash slot.
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