| Algorithm::Backoff::Exponential(3pm) | User Contributed Perl Documentation | Algorithm::Backoff::Exponential(3pm) |
Algorithm::Backoff::Exponential - Backoff exponentially
This document describes version 0.009 of Algorithm::Backoff::Exponential (from Perl distribution Algorithm-Backoff), released on 2019-06-20.
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
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".
Usage:
new(%args) -> obj
This function is not exported.
Arguments ('*' denotes required arguments):
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.
Number of seconds to wait after a success.
Initial delay for the first attempt after failure, in seconds.
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.
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.
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.
Maximum delay time, in seconds.
Maximum delay time, in seconds.
Return value: (obj)
Please visit the project's homepage at <https://metacpan.org/release/Algorithm-Backoff>.
Source repository is at <https://github.com/perlancar/perl-Algorithm-Backoff>.
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.
<https://en.wikipedia.org/wiki/Exponential_backoff>
Algorithm::Backoff
Other "Algorithm::Backoff::*" classes.
perlancar <perlancar@cpan.org>
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.
| 2022-10-22 | perl v5.34.0 |