Indexing Service is no longer supported as of Windows XP and is unavailable for use as of Windows 8. Instead, use Windows Search for client side search and Microsoft Search Server Express for server side search.
The MaxActiveQueryThreads entry is the maximum number of active threads to process queries made using ISAPI.
|Range:||1 - 1000|
The product of the value of the MaxActiveQueryThreads entry and the value of the IsapiRequestThresholdFactor entry establishes the maximum number of concurrently processed asynchronous queries made using ISAPI.