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I have problems with mutex timeouts. What can I do?



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My PRTG installation monitors about 100 EXE/Script sensors that each have a scanning interval of 1 hour. All of them have the same mutex. The runtime of each sensor is about six seconds, so there should not be any problem with the one-hour scanning interval.

However, I recently had the issue that all sensors are scanned at the same time. This results in the error message:

The request has timed out because the sensor is waiting for mutual exclusion (mutex). For more information, see https://kb.paessler.com/en/topic/57133. (code: PE035)

How can I achieve that PRTG distributes scanning a bit more over time to avoid those timeouts?

exe exe-script exe-script-sensor mutex mutex-timeout pe035 prtg timeout

Created on Aug 19, 2013 4:23:23 PM by  Gerald Schoch [Paessler Support]

Last change on Nov 29, 2019 11:40:12 AM by  Maike Guba [Paessler Support]

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This article applies to PRTG Network Monitor 19 or later

Mutex Timeouts (Code: PE035): Workaround

PRTG calculates the point in time when a sensor is scanned with a specific algorithm. To avoid overloading a device, all requests to one device are distributed as far as possible. However, if many sensors are distributed among many different devices—for example, one dedicated device for each folder in an OWA mailbox—the algorithm plans all requests for the same second. Of course, this approach results in problems in some specific cases.

A workaround for this issue is to cheat the algorithm a little bit:

  • The scanning distribution always begins with the first sensor of a device.
  • When you add other sensors to a device before certain mutex sensors, the mutex sensors will be scanned later.
  • For example, create some Green IT sensors as dummies. This sensor type does nothing but being green, and it has to be active.
  • The maximum scanning distance between two sensors on one device is 5 seconds. Thus, scanning succeeding sensors will be postponed 5 seconds per dummy sensor (if only very few sensors are on the same device).

If you apply this tweak to half of your EXE sensors, for example, it might be help enough because these sensors are scanned 5 seconds after the other sensors with the same mutex.

Note: As of PRTG 13.4.7, the starting points of scans on devices differ in 7 seconds. Because of this, all sensor scans are automatically distributed in a more consistent way.

More about EXE Sensors with Mutex and Corresponding Timeouts

Regarding EXE sensors, the mutex waits 3 times the timeout. You can define the timeout in the sensor settings. The maximum for mutex is 18 minutes. This is because after 20 minutes, a monitoring thread is killed the hard way.

If you have 100 sensors with 6 seconds of runtime each, this equals 10 minutes runtime in total, and a timeout of 4 minutes would be appropriate. Then, you would have a total timeout of 16 minutes: 4*3 (mutex) + 4 min (timeout). This is enough distance to the maximum runtime of 20 minutes but allows all sensors to wait up to 12 minutes.

Created on Aug 19, 2013 4:29:38 PM by  Gerald Schoch [Paessler Support]

Last change on Aug 2, 2019 6:46:36 AM by  Maike Guba [Paessler Support]

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Disclaimer: The information in the Paessler Knowledge Base comes without warranty of any kind. Use at your own risk. Before applying any instructions please exercise proper system administrator housekeeping. You must make sure that a proper backup of all your data is available.