overload(3erl) [linux man page]

overload(3erl)						     Erlang Module Definition						    overload(3erl)

NAME

       overload - An Overload Regulation Process

DESCRIPTION

       overload  is a process which indirectly regulates CPU usage in the system. The idea is that a main application calls the request/0 function
       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 param-
       eters, the MaxIntensity and the Weight value (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, provided that the value of exp(-Weight*(T(n) - T(n-1)) * AI(n-1) is less than MaxInten-
	   sity ; 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 will 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 , then a change in the  under-
       lying input intensity will be reflected in the total and accept intensities within approximately 10 seconds.

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

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

       A  new  overload  alarm	is not set until the current accept intensity has fallen below MaxIntensity . To prevent the overload process from
       generating a lot of set/reset alarms, the alarm is not reset until the current accept intensity has fallen below 75% of MaxIntensity ,  and
       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  should be processed with the job in question if the return value is accept ; otherwise it
	      should not 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 the current total and accept intensities, the configuration parameters, and absolute counts of the total number of requests,
	      and accepted number of requests (since the overload process was started).

SEE ALSO

       alarm_handler(3erl), sasl(3erl)

Ericsson AB							   sasl 2.1.9.3 						    overload(3erl)

Check Out this Related Man Page

alarm_handler(3erl)					     Erlang Module Definition					       alarm_handler(3erl)

NAME

       alarm_handler - An Alarm Handling Process

DESCRIPTION

       The  alarm  handler  process is a gen_event event manager process which receives alarms in the system. This process is not intended to be a
       complete alarm handler. It defines a place to which alarms can be sent. One simple event handler is  installed  in  the	alarm  handler	at
       start-up, but users are encouraged to write and install their own handlers.

       The  simple  event  handler  sends all alarms as info reports to the error logger, and saves all of them in a list which can be passed to a
       user defined event handler, which may be installed at a later stage. The list can grow large if many alarms are generated. So it is a  good
       reason to install a better user defined handler.

       There  are functions to set and clear alarms. The format of alarms are defined by the user. For example, an event handler for SNMP could be
       defined, together with an alarm MIB.

       The alarm handler is part of the SASL application.

       When writing new event handlers for the alarm handler, the following events must be handled:

	 {set_alarm, {AlarmId, AlarmDescr}} :
	   This event is generated by alarm_handler:set_alarm({AlarmId, AlarmDecsr}) .

	 {clear_alarm, AlarmId} :
	   This event is generated by alarm_handler:clear_alarm(AlarmId) .

       The default simple handler is called alarm_handler and it may be  exchanged  by	calling  gen_event:swap_handler/3  as  gen_event:swap_han-
       dler(alarm_handler,  {alarm_handler,  swap},  {NewHandler,  Args})  .  NewHandler:init({Args, {alarm_handler, Alarms}}) is called. Refer to
       gen_event(3erl) for further details.

EXPORTS

       clear_alarm(AlarmId) -> void()

	      Types  AlarmId = term()

	      Clears all alarms with id AlarmId .

       get_alarms() -> [alarm()]

	      Returns a list of all active alarms. This function can only be used when the simple handler is installed.

       set_alarm(alarm())

	      Types  alarm() = {AlarmId, AlarmDescription}
		     AlarmId = term()
		     AlarmDescription = term()

	      Sets an alarm with id AlarmId . This id is used at a later stage when the alarm is cleared.

SEE ALSO

       error_logger(3erl), gen_event(3erl)

Ericsson AB							   sasl 2.1.9.3 					       alarm_handler(3erl)

Linux and UNIX Man Pages

overload(3erl) [linux man page]

Check Out this Related Man Page