--- name: "Algorithm::Backoff::Exponential" section: "3pm" platform: "linux" package: "libalgorithm-backoff-perl" version: "0.010-2" release: "Debian 13 (Trixie)" platforms: ["linux"] url: "https://new.carta.tech/Algorithm::Backoff::Exponential" --- # Algorithm::Backoff::Exponential(3pm) Backoff exponentially ## NAME Algorithm::Backoff::Exponential - Backoff exponentially ## VERSION This document describes version 0.010 of Algorithm::Backoff::Exponential (from Perl distribution Algorithm-Backoff), released on 2024-02-24. ## SYNOPSIS ``` use Algorithm::Backoff::Exponential; # 1. instantiate my $ab = Algorithm::Backoff::Exponential->new( #consider_actual_delay => 1, # optional, default 0 #max_actual_duration => 0, # optional, default 0 (retry endlessly) #max_attempts => 0, # optional, default 0 (retry endlessly) #jitter_factor => 0.25, # optional, default 0 initial_delay => 5, # required #max_delay => 100, # optional #exponent_base => 2, # optional, default 2 (binary exponentiation) #delay_on_success => 0, # optional, default 0 ); # 2. log success/failure and get a new number of seconds to delay, timestamp is # optional but must be monotonically increasing. # for example, using the parameters initial_delay=5, max_delay=100: my $secs; $secs = $ab->failure(); # => 5 (= initial_delay) $secs = $ab->failure(); # => 10 (5 * 2^1) $secs = $ab->failure(); # => 20 (5 * 2^2) $secs = $ab->failure(); # => 33 (5 * 2^3 - 7) $secs = $ab->failure(); # => 80 (5 * 2^4) $secs = $ab->failure(); # => 100 ( min(5 * 2^5, 100) ) $secs = $ab->success(); # => 0 (= delay_on_success) ``` Illustration using CLI show-backoff-delays (10 failures followed by 3 successes): ``` % show-backoff-delays -a Exponential --initial-delay 1 --max-delay 200 \ 0 0 0 0 0 0 0 0 0 0 1 1 1 1 2 4 8 16 32 64 128 200 200 0 0 0 ``` ## DESCRIPTION This backoff algorithm calculates the next delay as: ``` initial_delay * exponent_base ** (attempts-1) ``` Only the `"initial_delay"` is required. `"exponent_base"` is 2 by default (binary exponential). For the first failure attempt (`"attempts"` = 1) the delay equals the initial delay. Then it is doubled, quadrupled, and so on (using the default exponent base of 2). There are limits on the number of attempts (\`max\_attempts\`) and total duration (\`max\_actual\_duration\`). It is recommended to add a jitter factor, e.g. 0.25 to add some randomness to avoid "thundering herd problem". ## METHODS ### new Usage: ``` new(%args) -> obj ``` This function is not exported. Arguments ('\*' denotes required arguments): - • **consider\_actual\_delay** =\> *bool* (default: 0) Whether to consider actual delay. If set to true, will take into account the actual delay (timestamp difference). For example, when using the Constant strategy of delay=2, you log **failure()** again right after the previous **failure()** (i.e. specify the same timestamp). **failure()** will then return ~2+2 = 4 seconds. On the other hand, if you waited 2 seconds before calling **failure()** again (i.e. specify the timestamp that is 2 seconds larger than the previous timestamp), **failure()** will return 2 seconds. And if you waited 4 seconds or more, **failure()** will return 0. - • **delay\_on\_success** =\> *ufloat* (default: 0) Number of seconds to wait after a success. - • **exponent\_base** =\> *ufloat* (default: 2) (No description) - • **initial\_delay**\* =\> *ufloat* Initial delay for the first attempt after failure, in seconds. - • **jitter\_factor** =\> *float* How much to add randomness. If you set this to a value larger than 0, the actual delay will be between a random number between original\_delay \* (1-jitter\_factor) and original\_delay \* (1+jitter\_factor). Jitters are usually added to avoid so-called "thundering herd" problem. The jitter will be applied to delay on failure as well as on success. - • **max\_actual\_duration** =\> *ufloat* (default: 0) Maximum number of seconds for all of the attempts (0 means unlimited). If set to a positive number, will limit the number of seconds for all of the attempts. This setting is used to limit the amount of time you are willing to spend on a task. For example, when using the Exponential strategy of initial\_delay=3 and max\_attempts=10, the delays will be 3, 6, 12, 24, ... If failures are logged according to the suggested delays, and max\_actual\_duration is set to 21 seconds, then the third **failure()** will return -1 instead of 24 because 3+6+12 \>= 21, even though max\_attempts has not been exceeded. - • **max\_attempts** =\> *uint* (default: 0) Maximum number consecutive failures before giving up. 0 means to retry endlessly without ever giving up. 1 means to give up after a single failure (i.e. no retry attempts). 2 means to retry once after a failure. Note that after a success, the number of attempts is reset (as expected). So if max\_attempts is 3, and if you fail twice then succeed, then on the next failure the algorithm will retry again for a maximum of 3 times. - • **max\_delay** =\> *ufloat* Maximum delay time, in seconds. - • **min\_delay** =\> *ufloat* (default: 0) Maximum delay time, in seconds. Return value: (obj) ## HOMEPAGE Please visit the project's homepage at \. ## SOURCE Source repository is at \. ## SEE ALSO \ Algorithm::Backoff Other `"Algorithm::Backoff::*"` classes. ## AUTHOR perlancar \ ## CONTRIBUTING To contribute, you can send patches by email/via RT, or send pull requests on GitHub. Most of the time, you don't need to build the distribution yourself. You can simply modify the code, then test via: ``` % prove -l ``` If you want to build the distribution (e.g. to try to install it locally on your system), you can install Dist::Zilla, Dist::Zilla::PluginBundle::Author::PERLANCAR, Pod::Weaver::PluginBundle::Author::PERLANCAR, and sometimes one or two other Dist::Zilla- and/or Pod::Weaver plugins. Any additional steps required beyond that are considered a bug and can be reported to me. ## COPYRIGHT AND LICENSE This software is copyright (c) 2024, 2019 by perlancar \. This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself. ## BUGS Please report any bugs or feature requests on the bugtracker website \ When submitting a bug or request, please include a test-file or a patch to an existing test-file that illustrates the bug or desired feature.