I have an interval that launches an AJAX call to check if there is any update for the page (I imagine that it's similar to the mechanism used by Facebook or StackExchange to check for new notifications). The problem is that this call changes the cursor to the 'progress' or 'busy' cursor (visual problem) and disables to option to click on links (functional problem).

I suppose both problems are related. How can get rid of this effect or at least minimize the consequences?

Some code:

setInterval(function() {
    try {
        var mid = $($("ul#alert-messages li.regular")[0]).attr('ref');
        call_ajax('/load_alerts', {num:0, id:mid}, function (data) {
            if (data.ok) {
                for (var i=0; i<data.result.length; i++) {
                    // ....
                }
                // ...
            }
        }, function() {},          // Do not show any error for this!!
        false);                    // Do not change cursor!
    } catch (e) {}
}, 15000);

function call_ajax(url, data, fnSuccess, fnError) {
    $.ajax({
        'url': url,
        'type': 'POST',
        'data': data,
        'dataType': "json",
        'success' : function(data) {
            if (fnSuccess) {
                fnSuccess(data);
            } else {
                if (typeof data.msg != 'undefined') {
                    topBar(data.msg, typeof data.ok != 'undefined' && data.ok? 'message' : 'error');
                }
            }
        },
        error : function (jqXHR, textStatus, errorThrown) {
            console.log(errorThrown);
            if (fnError) {
                fnError(STR_ERROR_AJAX + textStatus);
            } else {
                topBar(STR_ERROR_AJAX + textStatus, 'error');
            }
        }
    });
}