Considerations of a Distributed Messaging Queue’s Design

Before embarking on our journey to design a distributed messaging queue, let’s discuss some major factors that could significantly affect the design. These include the order of messages, the effect of the ordering on performance, and the management of concurrent access to the queue. We discuss each of these factors in detail below.

Ordering of messages

A messaging queue is used to receive messages from producers. These messages are consumed by the consumers at their own pace. Some operations are critical in that they require strict ordering of the execution of the tasks, driven by the messages in the queue. For example, while chatting over a messenger application with a friend, the messages should be delivered in order; otherwise, such communication can be confusing, to say the least. Similarly, emails received by a user from different users may not require strict ordering. Therefore, in some cases, the strict order of incoming messages in the queue is essential, while many use cases can tolerate some reordering.

Let’s discuss the following two categories of messages ordering in a queue:

• Best-effort ordering
• Strict ordering