presto-main/src/main/java/io/prestosql/operator/project/ConstantPageProjection.java/ConstantPageProjection/project
class ConstantPageProjection:    @Override
    public Work<Block> project(ConnectorSession session, DriverYieldSignal yieldSignal, Page page, SelectedPositions selectedPositions)
    {
        return new CompletedWork<>(new RunLengthEncodedBlock(value, selectedPositions.size()));
    }