---
name: "overload"
section: "3erl"
platform: "linux"
package: "erlang-manpages"
version: "1:17.3-dfsg-4+deb8u2"
release: "Debian 8 (Jessie)"
platforms: ["linux"]
url: "https://new.carta.tech/overload"
---

# overload(3erl)

An Overload Regulation Process

## 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 parameters, 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 *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 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 underlying 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)](/alarm_handler/3erl.md), sasl(3erl)