Managed queue

“Manage an explicit input queue, and react to its fill level.”

One of the conclusions drawn from analyzing the Pull pattern is that it can be used to mediate back pressure across multiple processing steps in a chain of components. Transmitting back pressure means halting the entire pipeline when the a consumer is momentarily overwhelmed, which may, for example, be caused by unfair scheduling or other execution artifacts, leading to avoidable inefficiencies in the system.

This kind of friction can lead to “stuttering” behavior in a processing engine, where short bursts of messages alternate with periods of inactivity during which back-pressure signals travel through the system. These bursts can be smoothed out by employing buffers that allow the data to keep flowing even during short back-pressure situations. These buffers are queues that temporarily hold messages while remembering their ordering. We call them managed queues because their use extends beyond this direct benefit: queues can be used to monitor and steer the performance of a messaging system. Buffering and managed queues are even more important at the boundaries of a system that employs back pressure: if data or requests are ingested from a source that cannot be slowed down, you need to mediate between the bounded internal capacity and the potentially unbounded influx.

back to the list