Algorithm::Backoff::Constant - Backoff using a constant delay


This document describes version 0.009 of Algorithm::Backoff::Constant (from Perl distribution Algorithm-Backoff), released on 2019-06-20.


 use Algorithm::Backoff::Constant;

 # 1. instantiate

 my $ab = Algorithm::Backoff::Constant->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, # optional, set to positive value to add randomness
     delay                  => 2, # required
     #delay_on_success      => 0, # optional, default 0

 # 2. log success/failure and get a new number of seconds to delay, timestamp is
 # optional argument (default is current time) but must be monotonically
 # increasing.

 my $secs = $ab->failure(1554652553); # => 2
 my $secs = $ab->success();           # => 0
 my $secs = $ab->failure();           # => 2

Illustration using CLI show-backoff-delays (5 failures followed by 3 successes):

 % show-backoff-delays -a Constant --delay 2 \
     0 0 0 0 0   1 1 1


This backoff strategy is one of the simplest: it waits X second(s) after each failure, or Y second(s) (default 0) after a success. There are limits on the number of attempts (`max_attempts`) and total duration (`max_actual_duration`). Some randomness can be introduced to avoid "thundering herd problem".




 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* => ufloat

    Number of seconds to wait after a failure.

  • delay_on_success => ufloat (default: 0)

    Number of seconds to wait after a success.

  • 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)


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Other Algorithm::Backoff::* classes.


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