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How the Exponential Backoff in Google Pub/Sub's RetryPolicy Works
Google Pub/Sub recently introduced a RetryPolicy feature to enhance error handling in server-side operations. The configuration options for this policy include MinimumBackoff and MaximumBackoff parameters.
MinimumBackoff and MaximumBackoff Configuration
The MinimumBackoff parameter specifies the initial wait period before the first retry. The MaximumBackoff parameter defines the maximum amount of time allowed between subsequent retries. These parameters correspond to the InitialInterval and MaxInterval in the exponential backoff algorithm implemented in github.com/cenkalti/backoff.
Exponential Backoff Algorithm
In exponential backoff, each randomized interval is calculated using the formula:
retryInterval = InitialInterval * (random value in range [1 - RandomizationFactor, 1 + RandomizationFactor])
where the InitialInterval is MinimumBackoff, and the random value introduces randomization in the retry delay. The retryInterval is capped by MaximumBackoff.
Example Program
The provided program demonstrates the behavior of the exponential backoff algorithm with different MinimumBackoff and MaximumBackoff values.
Observations from Program Output
Randomization and Multiplier
The exponential backoff algorithm used by RetryPolicy includes randomization to ensure that retries are not always made at the same interval. However, the provided program's output does not show a clear pattern of exponential growth in the retry intervals, suggesting that the Multiplier parameter, which would double the retry interval with each iteration, is not in use.
MaxElapsedTime
Unlike the exponential backoff implementation in github.com/cenkalti/backoff, RetryPolicy does not have an equivalent MaxElapsedTime parameter. This means that retries will continue indefinitely if the server is unavailable, unless the application handles and limits retries independently.
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