Exponential Backoff
Relates to:
Exponential Backoff is an algorithm that uses feedback to multiplicatively decrease the rate of some process, in order to gradually find an acceptable rate. In the strict sense of the word it is a closed-loop control system.
In computer systems often a simplified algorithm is used to implement a Retry Mechanism with Rate Limiting to prevent a DoS. (This is still considered “Exponential Backoff”, even though this is not a closed-loop control system). An example: If there is an Exception when sending a request, the system will wait 1, 2, 4, 8, 16, …, seconds respectively before trying again. To prevent very long delays after the situation has been restored, the maximum delay is often capped. I.e.: 1, 2, 4, 8, 8, 8, … seconds between retries.
Sometimes there is a situation that a request doesn’t result in an Exception, but that the service that has to handle the request is too busy. HTTP 429 is a mechanism to handle this scenario. (Note that if this happens that it may be an indication of a DoS in progress).