DataTables example Pipelining data to reduce Ajax calls for paging

Sever-side processing can be quite hard on your server, since it makes an Ajax call to the server for every draw request that is made. On sites with a large number of page views, you could potentially end up DDoSing your own server with your own applications!

This example shows one technique to reduce the number of Ajax calls that are made to the server by caching more data than is needed for each draw. This is done by intercepting the Ajax call and routing it through a data cache control; using the data from the cache if available, and making the Ajax request if not. This intercept of the Ajax request is performed by giving the ajaxDT option as a function. This function then performs the logic of deciding if another Ajax call is needed, or if data from the cache can be used.

Keep in mind that this caching is for paging only; the pipeline must be cleared for other interactions such as ordering and searching since the full data set, when using server-side processing, is only available at the server.

Processing...
First nameLast namePositionOfficeStart dateSalary
First nameLast namePositionOfficeStart dateSalary

The Javascript shown below is used to initialise the table shown in this example:

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//
// Pipelining function for DataTables. To be used to the `ajax` option of DataTables
//
$.fn.dataTable.pipeline = function ( opts ) {
    // Configuration options
    var conf = $.extend( {
        pages: 5,     // number of pages to cache
        url: '',      // script url
        data: null,   // function or object with parameters to send to the server
                      // matching how `ajax.data` works in DataTables
        method: 'GET' // Ajax HTTP method
    }, opts );
 
    // Private variables for storing the cache
    var cacheLower = -1;
    var cacheUpper = null;
    var cacheLastRequest = null;
    var cacheLastJson = null;
 
    return function ( request, drawCallback, settings ) {
        var ajax          = false;
        var requestStart  = request.start;
        var drawStart     = request.start;
        var requestLength = request.length;
        var requestEnd    = requestStart + requestLength;
         
        if ( settings.clearCache ) {
            // API requested that the cache be cleared
            ajax = true;
            settings.clearCache = false;
        }
        else if ( cacheLower < 0 || requestStart < cacheLower || requestEnd > cacheUpper ) {
            // outside cached data - need to make a request
            ajax = true;
        }
        else if ( JSON.stringify( request.order )   !== JSON.stringify( cacheLastRequest.order ) ||
                  JSON.stringify( request.columns ) !== JSON.stringify( cacheLastRequest.columns ) ||
                  JSON.stringify( request.search )  !== JSON.stringify( cacheLastRequest.search )
        ) {
            // properties changed (ordering, columns, searching)
            ajax = true;
        }
         
        // Store the request for checking next time around
        cacheLastRequest = $.extend( true, {}, request );
 
        if ( ajax ) {
            // Need data from the server
            if ( requestStart < cacheLower ) {
                requestStart = requestStart - (requestLength*(conf.pages-1));
 
                if ( requestStart < 0 ) {
                    requestStart = 0;
                }
            }
             
            cacheLower = requestStart;
            cacheUpper = requestStart + (requestLength * conf.pages);
 
            request.start = requestStart;
            request.length = requestLength*conf.pages;
 
            // Provide the same `data` options as DataTables.
            if ( $.isFunction ( conf.data ) ) {
                // As a function it is executed with the data object as an arg
                // for manipulation. If an object is returned, it is used as the
                // data object to submit
                var d = conf.data( request );
                if ( d ) {
                    $.extend( request, d );
                }
            }
            else if ( $.isPlainObject( conf.data ) ) {
                // As an object, the data given extends the default
                $.extend( request, conf.data );
            }
 
            settings.jqXHR = $.ajax( {
                "type":     conf.method,
                "url":      conf.url,
                "data":     request,
                "dataType": "json",
                "cache":    false,
                "success":  function ( json ) {
                    cacheLastJson = $.extend(true, {}, json);
 
                    if ( cacheLower != drawStart ) {
                        json.data.splice( 0, drawStart-cacheLower );
                    }
                    json.data.splice( requestLength, json.data.length );
                     
                    drawCallback( json );
                }
            } );
        }
        else {
            json = $.extend( true, {}, cacheLastJson );
            json.draw = request.draw; // Update the echo for each response
            json.data.splice( 0, requestStart-cacheLower );
            json.data.splice( requestLength, json.data.length );
 
            drawCallback(json);
        }
    }
};
 
// Register an API method that will empty the pipelined data, forcing an Ajax
// fetch on the next draw (i.e. `table.clearPipeline().draw()`)
$.fn.dataTable.Api.register( 'clearPipeline()', function () {
    return this.iterator( 'table', function ( settings ) {
        settings.clearCache = true;
    } );
} );
 
 
//
// DataTables initialisation
//
$(document).ready(function() {
    $('#example').dataTable( {
        "processing": true,
        "serverSide": true,
        "ajax": $.fn.dataTable.pipeline( {
            url: 'scripts/server_processing.php',
            pages: 5 // number of pages to cache
        } )
    } );
} );

In addition to the above code, the following Javascript library files are loaded for use in this example: