Provided by: libalgorithm-backoff-perl_0.009-3_all 
NAME
Algorithm::Backoff::MIMD - Multiplicative Increment, Multiplicative Decrement (MIMD)
backoff
VERSION
This document describes version 0.009 of Algorithm::Backoff::MIMD (from Perl distribution
Algorithm-Backoff), released on 2019-06-20.
SYNOPSIS
use Algorithm::Backoff::MIMD;
# 1. instantiate
my $ab = Algorithm::Backoff::MIMD->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
min_delay => 2, # optional, default 0
#max_delay => 100, # optional
initial_delay => 3, # required
delay_multiple_on_failure => 2, # required
delay_multiple_on_success => 0.5, # required
);
# 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=3,
# delay_multiple_on_failure=2, delay_multiple_on_success=0.5, min_delay=2:
my $secs;
$secs = $ab->failure(); # => 3 (= initial_delay)
$secs = $ab->failure(); # => 6 (3 * 2)
$secs = $ab->failure(); # => 12 (6 * 2)
$secs = $ab->success(); # => 6 (12 * 0.5)
$secs = $ab->success(); # => 3 (6 * 0.5)
$secs = $ab->success(); # => 2 (max(3*0.5, min_delay=2))
$secs = $ab->failure(); # => 4 (2 * 2)
Illustration using CLI show-backoff-delays (4 failures followed by 5 successes, followed
by 3 failures):
% show-backoff-delays -a MIMD --initial-delay 3 --min-delay 2 \
--delay-multiple-on-failure 2 --delay-multiple-on-success 0.5 \
0 0 0 0 1 1 1 1 1 0 0 0
3
6
12
24
12
6
3
2
2
4
8
16
DESCRIPTION
Upon failure, this backoff algorithm calculates the next delay as:
D1 = initial_delay
D2 = max(min(D1 * delay_multiple_on_failure, max_delay), min_delay)
...
Upon success, the next delay is calculated as:
D1 = initial_delay
D2 = max(min(D1 * delay_multiple_on_success, max_delay), min_delay)
...
"initial_delay", "delay_multiple_on_failure", and "delay_multiple_on_success" are
required. "initial_delay" and "min_delay" should be larger than zero; otherwise the next
delays will all be zero.
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_multiple_on_failure* => ufloat
How much to multiple previous delay, upon failure (e.g. 1.5).
• delay_multiple_on_success* => ufloat
How much to multiple previous delay, upon success (e.g. 0.5).
• 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 <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
Algorithm::Backoff::LILD
Algorithm::Backoff::LIMD
Algorithm::Backoff::MILD
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.