You are right for the performance of the UI virtualization of the RadDiagram. Unfortunately, we cannot create a good default virtualization algorithm that will cover every single scenario. The reason behind this is the fact that the RadDiagram can be used in many different scenarios.
However, If you provide us with more details about your real life application and your current implementation, we will be able to suggest approach that will increase the performance of the default UI virtualization.
Pavel R. Pavlov
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