DataTables server-side processing URL too long

if you use GET try to remove unnecessary column.

$('#your-table').DataTable({
  serverSide: true,
  processing: true,
  ajax: {
    url: 'url-here',
    data: function (data) {
      for (var i = 0, len = data.columns.length; i < len; i++) {
        if (! data.columns[i].search.value) delete data.columns[i].search;
        if (data.columns[i].searchable === true) delete data.columns[i].searchable;
        if (data.columns[i].orderable === true) delete data.columns[i].orderable;
        if (data.columns[i].data === data.columns[i].name) delete data.columns[i].name;
      }
      delete data.search.regex;
    }
  }
})

You can send it via POST instead, so none of those fields will appear on the URL sent to your server. Here's an example from the docs:

$(document).ready(function() {
    $('#example').DataTable( {
        "serverSide": true,
        "ajax": {
            "url": "scripts/post.php",
            "type": "POST"
        },
    };
});