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



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My PRTG monitors about 100 EXE/Script sensors which have a scanning interval of 1h each. All of them have the same mutex. The runtime of each sensor is about six seconds so there shouldn’t be any problem with the one hour interval.

However, I encountered recently that all sensors are scanned at the same time. This results in the error “Timeout caused by wait for mutex (Code: PE035)”. How can I achieve that PRTG distributes scanning a bit more over time in order 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 Feb 13, 2014 10:01:46 AM by  Gerald Schoch [Paessler Support]

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This article applies to PRTG Network Monitor 13 or later

Mutex Timeouts (Code: PE035): Workaround

PRTG calculates the point in time when a sensor is going to be scanned with a specific algorithm. In order to avoid overloading a device, all requests to one device are distributed as far as possible. Though, if there are many sensors spread over 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 for 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.
  • Adding 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, though, it has to be active.
  • The maximal 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 distributed in a more consistent way automatically.

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 runtime each which equals 10 minutes runtime in total, a timeout of 4 minutes would be appropriate. Then you have a total timeout of 16 minutes: 4*3 (mutex) + 4 min (timeout). This is enough distance to the maximal 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 Mar 3, 2014 12:14:06 PM by  Gerald Schoch [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.