How do Google Pub/Sub\'s RetryPolicy Parameters Relate to the ExponentialBackOff Library\'s InitialInterval and MaxInterval?

Exponential Backoff in RetryPolicy for Google Pub/Sub

Problem Statement

Google Pub/Sub's RetryPolicy includes MinimumBackoff and MaximumBackoff parameters. The documentation explains that these values are used for exponential backoff in discrete time. However, it does not provide details on how they relate to the InitialInterval and MaxInterval in the ExponentialBackOff library that is often used.

Backoff Mechanics

The documentation provides a glimpse of the backoff calculation, which resembles the approach taken by the ExponentialBackOff library:

randomized interval = RetryInterval * (random value in range [1 - RandomizationFactor, 1 + RandomizationFactor])

• RetryInterval is the current delay between retries, which starts at the value of MinimumBackoff and is capped by MaximumBackoff.
• RandomizationFactor provides a range of randomization around the RetryInterval.

Observations from the Examples

The test program provided illustrates the effect of varying backoff parameters on the actual delays between message nacks.

• With MinimumBackoff and MaximumBackoff set to 5s and 60s, respectively, the delays between nacks gradually increase, reaching 1 minute by the 6th attempt. This suggests a doubling of the RetryInterval after each attempt.
• With MinimumBackoff and MaximumBackoff set to 1s and 2s, respectively, the delays between nacks hover around 3s, indicating a consistent delay slightly above the MaximumBackoff value.

Multiplier and MaxElapsedTime

The Multiplier and MaxElapsedTime parameters, as defined in the ExponentialBackOff library, do not have direct equivalents in Google Pub/Sub's RetryPolicy.

• The Multiplier is not mentioned in the documentation, and the examples do not suggest that the delay doubles every time.
• The MaxElapsedTime is not explicitly supported, but the documentation states that retries will continue indefinitely if MaximumBackoff is set to 0.

Conclusion

The MinimumBackoff and MaximumBackoff parameters in Google Pub/Sub's RetryPolicy behave similarly to InitialInterval and MaxInterval in the ExponentialBackOff library, employing a randomized exponential backoff mechanism. However, Google Pub/Sub does not explicitly support a multiplier or a maximum elapsed time for retries.

The above is the detailed content of How do Google Pub/Sub\'s RetryPolicy Parameters Relate to the ExponentialBackOff Library\'s InitialInterval and MaxInterval?. For more information, please follow other related articles on the PHP Chinese website!