Hello Sodi We,
The data source components are declarative and they only specify how to obtain the data for the data item. They don't store or cache the data. Thus they are invoked once for every data item that is referencing the data source components. Additionally have in mind that the datasource parameters support expressions that can be report item contextual. In this line of thoughts if your data member execution is time and resource expensive our suggestion is implement in your DAL a data source caching mechanism.
All the best,
the Telerik team
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