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d5a6b0f99a
Despite its name, the `queue_size` method does not return the number of items in the queue; it returns the number of items that the local consumer has delivered but unprocessed. These are often, but not always, the same. RabbitMQ's queues maintain the queue of unacknowledged messages; when a consumer connects, it sends to the consumer some number of messages to handle, known as the "prefetch." This is a performance optimization, to ensure the consumer code does not need to wait for a network round-trip before having new data to consume. The default prefetch is 0, which means that RabbitMQ immediately dumps all outstanding messages to the consumer, which slowly processes and acknowledges them. If a second consumer were to connect to the same queue, they would receive no messages to process, as the first consumer has already been allocated them. If the first consumer disconnects or crashes, all prior events sent to it are then made available for other consumers on the queue. The consumer does not know the total size of the queue -- merely how many messages it has been handed. No change is made to the prefetch here; however, future changes may wish to limit the prefetch, either for memory-saving, or to allow multiple consumers to work the same queue. Rename the method to make clear that it only contains information about the local queue in the consumer, not the full RabbitMQ queue. Also include the waiting message count, which is used by the `consume()` iterator for similar purpose to the pending events list. |
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| __init__.py | ||
| queue_processors.py | ||