Cannot work with scroll in datatable for server-side processing ?

matt.crawfoord

i try to shows scroller using server-side processing mode to my datatable , but it's show nothing .
Question 1. when i remove the scroll ,datatable work success ,what's problem with my scroll code ?
Question 2. because i am using server-side processing, from my code is setting 5000000, but how to set iTotalDisplayRecords from my json data to replace 5000000?

part of my json data

{
"iTotalRecords": 69511,
"iTotalDisplayRecords": 69511,
"aaData": [
    {
        "message":.........

javascript code ,

 $(document).ready(function() {

 var table = $('#example').DataTable( {
    "ajax": {
        url : "process.php",
            type: 'POST',
                    data: {
                    from: "<?php echo $from; ?>",
                            },
        setTimeout( function () {
                     callback( {
                     draw: data.draw,
                    data: data,
                    recordsTotal: 5000000,
                    recordsFiltered: 5000000
                     } );
                     }, 50 );
    },
    "scrollY": 200,
             "scroller": {
             loadingIndicator: true
                            },
     "columns": [
        {
            "className":      'details-control',
            "orderable":      false,
            "data":           null,
            "defaultContent": ''
        },
        { "data": "time" },
        { "data": "message" }
    ],
    "order": [[1, 'asc']]
} );


// Add event listener for opening and closing details
$('#example tbody').on('click', 'td.details-control', function () {
    var tr = $(this).closest('tr');
    var row = table.row( tr );

    if ( row.child.isShown() ) {
        // This row is already open - close it
        row.child.hide();
        tr.removeClass('shown');
    }
    else {
        // Open this row
        row.child( format( row.data())).show();
        tr.addClass('shown');
    }
} );