Exponential backoff

Exponential backoff is a standard error handling strategy for network applications in which a client periodically retries a failed request with increasing delays between requests. Clients should use exponential backoff for all requests to Cloud Memorystore for Redis that return HTTP 5xx and 429 response code errors.

Understanding how exponential backoff works is important if you are:

If you are using the Google Cloud Platform Console, the console sends requests to Cloud Memorystore for Redis on your behalf and handles any necessary backoff.

Example algorithm

An exponential backoff algorithm retries requests exponentially, increasing the waiting time between retries up to a maximum backoff time. An example is:

  1. Make a request to Cloud Memorystore for Redis.

  2. If the request fails, wait 1 + random_number_milliseconds seconds and retry the request.

  3. If the request fails, wait 2 + random_number_milliseconds seconds and retry the request.

  4. If the request fails, wait 4 + random_number_milliseconds seconds and retry the request.

  5. And so on, up to a maximum_backoff time.

  6. Continue waiting and retrying up to some maximum number of retries, but do not increase the wait period between retries.

where:

  • The wait time is min(((2^n)+random_number_milliseconds), maximum_backoff), with n incremented by 1 for each iteration (request).

  • random_number_milliseconds is a random number of milliseconds less than or equal to 1000. This helps to avoid cases where many clients get synchronized by some situation and all retry at once, sending requests in synchronized waves. The value of random_number_milliseconds should be recalculated after each retry request.

  • maximum_backoff is typically 32 or 64 seconds. The appropriate value depends on the use case.

It's okay to continue retrying once you reach the maximum_backoff time. Retries after this point do not need to continue increasing backoff time. For example, if a client uses an maximum_backoff time of 64 seconds, then after reaching this value, the client can retry every 64 seconds. At some point, clients should be prevented from retrying infinitely.

The maximum backoff and maximum number of retries that a client uses depends on the use case and network conditions. For example, mobile clients of an application may need to retry more times and for longer intervals when compared to desktop clients of the same application.

If the retry requests fail after exceeding the maximum number of retries, report or log an error using one of the methods listed under Getting support.

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Google Cloud Memorystore for Redis