NAME

       overload - An Overload Regulation Process

DESCRIPTION

   Warning:
       All functions in this module are deprecated and will be removed in a future release.

       overload  is  a  process  that  indirectly regulates the CPU usage in the system. The idea is that a main
       application calls function request/0 before starting a major job and proceeds with the job if the  return
       value is positive; otherwise the job must not be started.

       overload is part of the SASL application and all configuration parameters are defined there.

       A  set of two intensities are maintained, the total intensity and the accept intensity. For that purpose,
       there are two configuration parameters, MaxIntensity and Weight; both are measured in 1/second.

       Then total and accept intensities are calculated as follows. Assume that the time of the current call  to
       request/0 is T(n) and that the time of the previous call was T(n-1).

         * The current total intensity, denoted TI(n), is calculated according to the formula

           TI(n) = exp(-Weight*(T(n) - T(n-1)) * TI(n-1) + Weight,

           where TI(n-1) is the previous total intensity.

         * The current accept intensity, denoted AI(n), is determined by the formula

           AI(n) = exp(-Weight*(T(n) - T(n-1)) * AI(n-1) + Weight,

           where AI(n-1) is the previous accept intensity, if the value of exp(-Weight*(T(n) - T(n-1)) * AI(n-1)
           is less than MaxIntensity. Otherwise the value is

           AI(n) = exp(-Weight*(T(n) - T(n-1)) * AI(n-1)

       The value of configuration parameter Weight controls the speed with which the calculations of intensities
       react  to  changes  in the underlying input intensity. The inverted value of Weight, T = 1/Weight, can be
       thought of as the "time constant" of the intensity calculation formulas. For example, if Weight = 0.1,  a
       change  in  the  underlying  input  intensity is reflected in total intensity and accept intensity within
       about 10 seconds.

       The overload process defines one alarm, which it  sets  using  alarm_handler:set_alarm(Alarm).  Alarm  is
       defined as follows:

         {overload, []}:
           This alarm is set when the current accept intensity exceeds MaxIntensity.

       A  new  request  is  not  accepted  until  the current accept intensity has fallen below MaxIntensity. To
       prevent the overload process from generating many set/reset alarms, the alarm  is  not  reset  until  the
       current accept intensity has fallen below 75% of MaxIntensity; it is not until then that the alarm can be
       set again.

EXPORTS

       request() -> accept | reject

              Returns accept or reject depending on the current value of the accept intensity.

              The  application  calling this function is to proceed with the job in question if the return value
              is accept; otherwise it is not to continue with that job.

       get_overload_info() -> OverloadInfo

              Types:

                 OverloadInfo  =  [{total_intensity,   TotalIntensity},   {accept_intensity,   AcceptIntensity},
                 {max_intensity,    MaxIntensity},    {weight,    Weight},    {total_requests,   TotalRequests},
                 {accepted_requests, AcceptedRequests}].
                 TotalIntensity = float() > 0
                 AcceptIntensity = float() > 0
                 MaxIntensity = float() > 0
                 Weight = float() > 0
                 TotalRequests = integer()
                 AcceptedRequests = integer()

              Returns:

                * Current total and accept intensities

                * Configuration parameters

                * Absolute counts of the total number of requests

                * Accepted number of requests (since the overload process was started)

SEE ALSO

       alarm_handler(3erl), sasl(7)

Ericsson AB                                         sasl 2.7                                      overload(3erl)