The fan-out and quickest-reply reactive design pattern emphasizes rapid processing. Financial software that provides real-time, or near real-time, stock information uses this design pattern. The concept is to provide sufficient processing instances so requests can be processed without waiting in a queue.

To implement the fan-out and quickest-reply design pattern, we send each request to multiple processing modules. Each of those modules would process the request and send the results back to the requestor. The requestor would use the quickest reply, the first one received, and simply ignore the rest:

As you would expect, the extra processing could make it a costly use of resources, so this approach should only be used when quick replies are of utmost importance.

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