How the DMRC Determines When to Search the WMIS Server

The device metadata retrieval client (DMRC) maintains a cache of device metadata packages. This cache is populated with metadata packages that the DMRC downloaded from the Windows Metadata and Internet Services (WMIS) server.

When the Devices and Printers or Device Stage user interfaces (UIs) are opened, the DMRC searches its cache for the most appropriate and current metadata package of every device that is displayed in the UI.

Periodically, before it selects a metadata package from its cache, the DMRC searches for a newer metadata package for a device on the WMIS server. If one is found, the DMRC downloads the package and installs it in its cache on the computer. Then, the DMRC selects the newer version of the metadata package from its cache.

Based on the following values, the DMRC determines when to search the WMIS server for a newer metadata package for a device:

LastCheckedDate

This value indicates the most recent date when the DMRC queried the WMIS server for metadata for a device. This date does not reflect whether the DMRC successfully downloaded a metadata package.

The DMRC manages an index table that contains the properties for the device metadata package of each device ID in the system. The LastCheckedDate value is a field of each row in this index table.

CheckBackMDNotRetrieved

This registry value indicates the number of days that the DMRC waits before it repeats a query of the WMIS server for a device metadata package. This value applies to devices for which the DMRC has not yet downloaded metadata from WMIS.

The CheckBackMDNotRetrieved value is located under the following registry key:

HKCU\Software\Microsoft\Windows\CurrentVersion\DeviceMetadata

The following table describes the format and value range for the CheckBackMDNotRetrieved value.

Data typeValue rangeDefault value
REG_DWORD0 to 256, inclusive5

 

CheckBackMDRetrieved

This registry value indicates the number of days that the DMRC waits before it queries for updated device metadata packages. This value applies to devices for which the DMRC previously downloaded metadata packages.

The CheckBackMDRetrieved value is located under the following registry key:

HKCU\Software\Microsoft\Windows\CurrentVersion\DeviceMetadata

The following table describes the format and value range for the CheckBackMDRetrieved value.

Data typeValue rangeDefault value
REG_DWORD0 to 256, inclusive8

 

Note  The WMIS server, in cooperation with the DMRC, sets the values for the CheckBackMDRetrieved and CheckBackMDNotRetrieved registry values on the client system. These values are set based on network conditions and load balancing. Every response from the WMIS server contains the client configuration data and controls the DMRC behavior.

The DMRC follows these steps to determine whether it has to search the WMIS server for a newer metadata package for a device:

  1. If the target device?s device ID is not listed in the DMRC index table, the DMRC is searching for the device's metadata package for the first time. In this case, the DMRC queries the WMIS server.

  2. If the target device?s device ID is listed in the DMRC index table, the DMRC calculates whether it is time to query the WMIS server again for a metadata package for the device. In this case, the DMRC queries the WMIS server in the following way:

    1. If the DMRC has previously downloaded a device metadata package for the device, the DMRC compares the value of the CheckBackMDRetrieved registry key to the value of today's date minus the LastCheckedDate value. If the CheckBackMDRetrieved value is smaller, the DMRC queries the WMIS server.

    2. If the DMRC has not previously downloaded a device metadata package for the device, the DMRC compares the value of the CheckBackMDNotRetrieved registry key to the value of today's date minus the LastCheckedDate value. If the CheckBackMDNotRetrieved value is smaller, the DMRC queries the WMIS server.

 

 

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