NAME

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

VERSION

This document describes version 0.003 of Algorithm::Backoff::Fibonacci (from Perl distribution Algorithm-Backoff), released on 2019-04-10.

SYNOPSIS

 use Algorithm::Backoff::Fibonacci;

 # 1. instantiate

 my $ar = Algorithm::Backoff::Fibonacci->new(
     #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 = $ar->failure();   # =>  2 (= initial_delay1)
 $secs = $ar->failure();   # =>  3 (= initial_delay2)
 $secs = $ar->failure();   # =>  5 (= 2+3)
 $secs = $ar->failure();   # =>  8 (= 3+5)
 sleep 1;
 $secs = $ar->failure();   # => 12 (= 5+8 -1)
 $secs = $ar->failure();   # => 20 (= min(13+8, 20) = max_delay)

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

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. It is recommended to add a jitter factor, e.g. 0.25 to add some randomness.

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.

  • 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.

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.

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.

SEE ALSO

https://en.wikipedia.org/wiki/Fibonacci_number

Algorithm::Backoff

Other Algorithm::Backoff::* classes.

AUTHOR

perlancar <perlancar@cpan.org>

COPYRIGHT AND LICENSE

This software is copyright (c) 2019 by 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.