How does virtual scrolling work under the hood?
If I use virtual scrolling with a database datasource, will KoolGrid fetch records in 1 resultset or will KoolGrid fetch all results in in chunks?
And, compared with ArrayDataSource or AdvancedArrayDataSource, will KoolGrid fetch records in 1 resultset or will KoolGrid fetch all results in in chunks?

Virtual scrolling loading data in chunks. Based on the scrolling position of user, KoolGrid will calculate and load the corresponding page or chunk.
The ArrayDataSource and AdvancedArrayDataSource will load the whole set at server-side because those class act like a fake database. At the client-side KoolGrid loads data by chunks.