Algorithm::Backoff::Fibonacci(3)

NAME
Algorithm::Backoff::Fibonacci - Backoff using Fibonacci sequence

VERSION
This document describes version 0.010 of Algorithm::Backoff::Fibonacci (from Perl distribution Algorithm-Backoff), released on 2024-02-24.

SYNOPSIS
 use Algorithm::Backoff::Fibonacci;

 # 1. instantiate

 my $ab = Algorithm::Backoff::Fibonacci->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_delay1         => 2, # required
     initial_delay2         => 3, # required
     #max_delay             => 20, # optional
     #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.

 my $secs;
 $secs = $ab->failure();   # =>  2 (= initial_delay1)
 $secs = $ab->failure();   # =>  3 (= initial_delay2)
 $secs = $ab->failure();   # =>  5 (= 2+3)
 $secs = $ab->failure();   # =>  8 (= 3+5)
 sleep 1;
 $secs = $ab->failure();   # => 12 (= 5+8 -1)
 $secs = $ab->failure();   # => 20 (= min(13+8, 20) = max_delay)

 $secs = $ab->success();   # =>  0 (= delay_on_success)

Illustration using CLI show-backoff-delays (10 failures followed by 3 successes):

 % show-backoff-delays -a Fibonacci --initial-delay1 0 --initial-delay2 1 \
     0 0 0 0 0   0 0 0 0 0   1 1 1
 0
 1
 1
 2
 3
 5
 8
 13
 21
 34
 0
 0
 0

DESCRIPTION
This backoff algorithm calculates the next delay using Fibonacci sequence. For example, if the two initial numbers are 2 and 3:

 2, 3, 5, 8, 13, 21, ...

"initial_delay1" and "initial_delay2" are required. The other attributes are optional.

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.

•   initial_delay1* => ufloat

    Initial delay for the first attempt after failure, in seconds.

•   initial_delay2* => ufloat

    Initial delay for the second 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 <https://metacpan.org/release/Algorithm-Backoff>.

SOURCE
Source repository is at <https://github.com/perlancar/perl-Algorithm-Backoff>.

SEE ALSO
<https://en.wikipedia.org/wiki/Fibonacci_number>

Algorithm::Backoff

Other "Algorithm::Backoff::*" classes.

AUTHOR
perlancar <perlancar@cpan.org>

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 <perlancar@cpan.org>.

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 <https://rt.cpan.org/Public/Dist/Display.html?Name=Algorithm-Backoff>

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.