1164661 - taskcluster-client: Implement randomization factor for retries

Status: RESOLVED FIXED

(Taskcluster :: General, defect)

Description

[Jonas Finnemann Jensen (:jonasfj)]

We should have a randomization factor, as a percentage that can be randomly added/subtracted from the computed retry delay.

Example:
  delay is computed to 5s
  randomization factor is 0.5
  randomized delay is in [2.5; 7.5]

I doubt it's critical, but probably nice to have, and really cheap.

Comment 1

[Jonas Finnemann Jensen (:jonasfj)]

Attachment: Github PR

Let me know if this is crazy... Thanks,

I'm aiming to do somewhat the same as you do in go..
Granted I stole this from:
http://javadoc.google-http-java-client.googlecode.com/hg/1.17.0-rc/com/google/api/client/util/ExponentialBackOff.html
And a few others that seemed to use the exact same logic.

Comment 2

[Pete Moore [:pmoore][:pete]]

Comment on attachment 8616916 [details] [review]
Github PR

Thanks Jonas. I double checked the maths, and all looks good!

(Math.random() - 0.5) : gives a result in [-0.5, 0.5)
=> rf * 2 * (Math.random() - 0.5) : gives a result in [-rf, +rf)
=> 1 + rf * 2 * (Math.random() - 0.5) : gives a result in [1-rf, 1+rf)
=> delay * (1 + rf * 2 * (Math.random() - 0.5)) : gives a result in [delay - delay * rf, delay + delay * rf] = adjusted delay we want

expanding: rf * 2 * (Math.random() - 0.5) = 2 * Math.random() * rf - rf gives:

adjusted delay = delay * (1 + 2 * Math.random() * rf - rf)

which is the same as the result you reached! :)

Comment 3

[Jonas Finnemann Jensen (:jonasfj)]

Merged and landed in tc-client v 0.22.2

Comment 4

[Pete Moore [:pmoore][:pete]]

Resetting Version and Target Milestone that accidentally got changed...