feat: allow strategies other than polynomial

[galargh]

Resolves #ISSUE_NUMBER (not applicable; issue does not exist)

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Behavior

Before the change?

• The plugin always performs retries using polynomial strategy (RETRY_AFTER_BASE * (RETRY_COUNT + 1)^2)

After the change?

• The plugin accepts strategy as an option.
• The accepted values are
  • exponential (RETRY_AFTER_BASE * 2^(RETRY_COUNT + 1))
  • linear (RETRY_AFTER_BASE * (RETRY_COUNT + 1))
  • polynomial (RETRY_AFTER_BASE * (RETRY_COUNT + 1)^2)
• If no strategy is provided, the plugin uses polynomial strategy (backwards compatible).
• The plugins throws an error if an invalid strategy name is provided.

Other information

• not applicable

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Additional info

Pull request checklist

• Tests for the changes have been added (for bug fixes / features)
• Docs have been reviewed and added / updated if needed (for bug fixes / features)
• Added the appropriate label for the given change

Does this introduce a breaking change?

Please see our docs on breaking changes to help!

• Yes (Please add the Type: Breaking change label)
• No (I think it should fall under Adding optional parameters to existing SDK APIs)

If Yes, what's the impact:

• N/A

Pull request type

• Feature/model/API additions: Type: Feature

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[nickfloyd]

Hey @galargh, thanks for the changes here ❤️ - I just had a few questions/thoughts on your change, let me know what you think!

[nickfloyd]

You have base inverted with your power - You'll need to do:Math.pow(base, exp).

Also, you might want to wrap this in Math.round(Math.pow(base, exp)) just because pow returns a double

[galargh]

Thanks! I renamed base variable to retryCount so that it's a bit less confusing. I also wrapped it in Math.round as suggested.

It reads as following now:

Math.round(Math.pow(2, retryCount))

As for the inversion, as per https://en.wikipedia.org/wiki/Exponential_backoff, exponential backoff is formed by taking the multiplicative factor (in this case 2) to the power of the number of observed events (in this case the number of retries that have already been performed). So I think it is correct now. Let me know if you wanted me to use different names though.

[nickfloyd]

For the polynomial strategy, you'll want Math.pow(2, base)

Also, you might want to wrap this in Math.round(Math.pow(base, exp)) just because pow returns a double

[galargh]

Wrapped Math.pow with Math.round - great spot, thanks 😄

As mentioned in #412 (comment), I think that would make it exponential backoff.

Full disclosure, I named this one polynomial by looking at what others tool call it (e.g. https://backoff-utils.readthedocs.io/en/latest/strategies.html#polynomial).