Retry backoff docs?

[MarkMurphy]

According to the wiki here: https://github.com/mperham/sidekiq/wiki/Error-Handling

The default retry backoff algorithm is:

(retry_count ** 4) + 15 + (rand(30) * (retry_count + 1))

The wiki claims that the default 25 count retry using this algorithm spans ~21 days however I only get ~4 days when I put that to the test:

> (0..25).each do |retry_count| 
  puts (retry_count ** 4) + 15 + (rand(30) * (retry_count + 1))
end

35
22
76
144
371
796
1402
2624
4264
6786
10257
14704
20816
28660
38836
50848
66010
83950
105523
130756
160099
194826
234685
280456
332016
391342

Am I miss-understanding something?

[aprescott]

The nth retry happens after the previous n-1 retries, so you have to consider the cumulative time spent getting to the nth retry. Barring off-by-one errors in my code, I think this is the more accurate time:

def retry_for(retry_count)
  (retry_count ** 4) + 15 + (rand(30) * (retry_count + 1))
end

(1..25).each do |n|
  cumulative_days = (1..n).map { |x| retry_for(x) }.inject(:+).to_f / (60 * 60 * 24)
  puts "#{cumulative_days} days for retry attempt #{n}"
end

# 0.000787037037037037 days for retry attempt 1
# 0.0013078703703703703 days for retry attempt 2
# 0.003993055555555555 days for retry attempt 3
# 0.006400462962962963 days for retry attempt 4
# 0.015925925925925927 days for retry attempt 5
# 0.0340162037037037 days for retry attempt 6
# 0.06439814814814815 days for retry attempt 7
# 0.11091435185185185 days for retry attempt 8
# 0.18971064814814814 days for retry attempt 9
# 0.30571759259259257 days for retry attempt 10
# 0.47291666666666665 days for retry attempt 11
# 0.7178472222222222 days for retry attempt 12
# 1.0547916666666666 days for retry attempt 13
# 1.4991087962962963 days for retry attempt 14
# 2.0853819444444444 days for retry attempt 15
# 2.8479282407407407 days for retry attempt 16
# 3.8154050925925924 days for retry attempt 17
# 5.029976851851852 days for retry attempt 18
# 6.559722222222222 days for retry attempt 19
# 8.407662037037037 days for retry attempt 20
# 10.647604166666667 days for retry attempt 21
# 13.372638888888888 days for retry attempt 22
# 16.627037037037038 days for retry attempt 23
# 20.459085648148147 days for retry attempt 24
# 24.980717592592594 days for retry attempt 25

[mperham]

Yes, you need to add the retry times together! Looks like it's closer to 25 days:

> i = 0 ; (0..25).each { |retry_count| i += (retry_count ** 4) + 15 + (rand(30) * (retry_count + 1)) }; i
=> 2159131
> i / 86400.0
=> 24.98994212962963

With 0..24, it's 20.5 days so someone probably has an off-by-one.

[aprescott]

@mperham snap :)

[MarkMurphy]

Ah, makes sense! Thanks guys