Werk #5411

ComponentChecks & Agents
TitleWindows agent: handle WMI timeouts
Date2017-11-22 11:38:56
Check_MK EditionCheck_MK Raw Edition (CRE)
Check_MK Version1.4.0p21,1.5.0i2
Level1 - Trivial Change
ClassBug Fix
CompatibilityCompatible - no manual interaction needed

All sections depending on WMI (Windows Management Instrumentation) queries have been suffering from periodic freezing, the time interval between subsequent freezes being typically 18...20 minutes. At those moments, the Windows agent has not been delivering any output for some of its WMI-dependent sections (e. g., ps, uptime, dotnet_clrmemory, wmi_cpuload, msexch and wmi_webservices). The corresponding checks have issued error messages of type "Missing agent sections...". Various strategies have been previously used attempting to cope with the periodic problems with WMI. Werk #4008 introduced a timeout of 10s in order to prevent the agent from completely blocking if a WMI query freezes. However, this led to the described problem of missing agent output totally when no response was given to a WMI query within 10s. Moreover, multiple WMI queries waiting for 10s after another led to periodic long execution times of the Windows agent.

This Werk introduces a new strategy for coping with the periodic freezing of WMI queries. The timeout of the queries is reduced to 2.5s instead of 10s per query, reducing the total execution time of the Windows agent by approximately 75% when the problem occurs. Upon a WMI timeout, the Windows agent issues it in its output so, that the affected checks can tolerate it by setting their state to UNKNOWN. In normal cases, the check should get back to OK when the agent is contacted the next time and the WMI freeze is most likely gone.

There seems to be a connection of the WMI freezes to the Windows service WMI Performance Adapter. https://lokna.no/?p=1430 suggests that the startup type of this service be set to automatic, ensuring the service is running. Without this, the WMI Performance Adapter seems to get started periodically when WMI is queried. Testing with WMI Performance Adapter service running has showed clear signs of improvement, reducing the frequency of freezing WMI queries even if not completely ending them.