Queue Purge & Delete

Queue.Purge and Queue.Delete are easily confused but semantically very different: the former only empties a queue's contents, the latter removes the queue itself. RobustMQ implements real semantics for both, with safety checks.

Queue.Purge: Empty While Keeping the Queue

Queue.Purge doesn't remove the queue's metadata or declaration — it only deletes every message currently piled up in the queue:

• The implementation deletes each partition's records up to that partition's current high watermark — effectively "clear up to the latest position" rather than a logical tombstone.
• The queue's declaration, bindings, and shared consume group are all left untouched — publishing and consuming can resume right after purging.
• Queue.Purge-Ok returns the number of purged messages (message_count), a real count, not a placeholder.

Queue.Delete: Removing the Queue Itself

Queue.Delete completely removes the queue, which involves:

1. Deleting the queue's metadata (storage.delete_queue()).
2. Removing it from the broker's local cache.
3. Explicitly destroying the underlying storage shard (delete_storage_resource) — this step matters: without cleaning up the underlying shard, redeclaring a queue with the same name could "resurrect" old messages. RobustMQ explicitly avoids this.

Safety Checks: if-unused and if-empty

Queue.Delete supports two protective flags, both genuinely validated by RobustMQ:

• if-empty=true: if the queue still has messages (message_count > 0), the delete is rejected with 406 PRECONDITION_FAILED.
• if-unused=true: if the queue still has consumers (determined via the shared consume group's member count), the delete is rejected, also with 406 PRECONDITION_FAILED.

Both checks run before the delete actually executes, preventing an in-use queue from being accidentally removed.

Example (Java Client)

// Empty while keeping the queue
AMQP.Queue.PurgeOk purgeOk = channel.queuePurge("orders-queue");
System.out.println("purged: " + purgeOk.getMessageCount());

// Only deletes if the queue is empty and has no consumers
channel.queueDelete("orders-queue", true, true);

Further Reading

• Storage
• Core Concepts
• Shared Queue Group