getMaximumAllowedItems should have a reasonable minimum

[tomivirkki]

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Description of the bug

The getMaximumAllowedItems() algorithm in DataCommunicator should have a reasonable minimum.

The current maximum allowed items / data request is determined with the pattern 10 * pageSize. With a very small page size (like 1), the limit becomes too small and can easily result in missing data.

For example, if you set the Grid's pageSize to be 1, the limit becomes 10 items / request. However, Grid will request enough many pages to try to cover the viewport + some additional padding and this easily exceeds the new safety limit of 10 items.

A reasonable minimum (for example 500 items) should be used in the algorithm so that the maximum is calculated with max((10 * pageSize), 500) instead of (10 * pageSize).

Issue extracted from https://github.com/vaadin/flow-components/issues/3708

Expected behavior

Small page size should not result in too small a limit for maximum allowed items

Minimal reproducible example

var grid = new Grid<Integer>();
grid.setPageSize(1);
grid.addColumn(ValueProvider.identity()).setHeader("Column 1");
grid.setItems(IntStream.range(0, 20).boxed().toArray(Integer[]::new));
add(grid);

results in:

With a warning: [qtp1663626008-46] WARN com.vaadin.flow.data.provider.DataCommunicator - Attempted to fetch more items from server than allowed in one go: number of items requested '21', maximum items allowed '10'.

Versions

• Vaadin / Flow version: 21.0.4 upwards