I would suggest you to use a WebService to bind the RadAutoComplteBox with data and use the private method _requestItems("")
at page load (at client-side). Thus you will manually initiate request to the web service and populate the control initially with the needed data. This approach will provide you with the ability to customize the queries to the database and return the needed results - initially 100 and then filtering against the entire datasource.
In addition in the attachment you could find a simple project, demonstrating the implementation of the above suggestion. The thing you need to modify is the access to your database and the needed filtering.
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