Pipelining data to reduce Ajax calls for paging

Server-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 ajax 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.

First name	Last name	Position	Office	Start date	Salary
First name	Last name	Position	Office	Start date	Salary

Javascript
HTML
CSS
Ajax
Server-side script
Comments

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

//
// 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 (typeof conf.data === 'function') {
				// 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);
			}

			return $.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);
					}
					if (requestLength >= -1) {
						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()`)
DataTable.Api.register('clearPipeline()', function () {
	return this.iterator('table', function (settings) {
		settings.clearCache = true;
	});
});

//
// DataTables initialisation
//
$('#example').DataTable({
	ajax: DataTable.pipeline({
		url: 'scripts/server_processing.php',
		pages: 5 // number of pages to cache
	}),
	processing: true,
	serverSide: true
});

//
// Pipelining function for DataTables. To be used to the `ajax` option of DataTables
//
DataTable.pipeline = function (opts) {
	// Configuration options
	var conf = Object.assign(
		{
			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 async 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 = JSON.parse(JSON.stringify(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 (typeof conf.data === 'function') {
				// 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) {
					Object.assign(request, d);
				}
			}
			else if (conf.data) {
				// As an object, the data given extends the default
				Object.assign(request, conf.data);
			}

			// Use `fetch` to make Ajax request
			let response = await fetch(
				conf.url + '?json=' + JSON.stringify(request),
				{
					method: conf.method
				}
			);

			let json = await response.json();

			cacheLastJson = JSON.parse(JSON.stringify(json));

			if (cacheLower != drawStart) {
				json.data.splice(0, drawStart - cacheLower);
			}
			if (requestLength >= -1) {
				json.data.splice(requestLength, json.data.length);
			}

			drawCallback(json);
		}
		else {
			json = JSON.parse(JSON.stringify(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()`)
DataTable.Api.register('clearPipeline()', function () {
	return this.iterator('table', function (settings) {
		settings.clearCache = true;
	});
});

//
// DataTables initialisation
//
$('#example').DataTable({
	ajax: DataTable.pipeline({
		url: 'scripts/server_processing.php',
		pages: 5 // number of pages to cache
	}),
	processing: true,
	serverSide: true
});

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

The HTML shown below is the raw HTML table element, before it has been enhanced by DataTables:

This example uses a little bit of additional CSS beyond what is loaded from the library files (below), in order to correctly display the table. The additional CSS used is shown below:

The following CSS library files are loaded for use in this example to provide the styling of the table:

This table loads data by Ajax. The latest data that has been loaded is shown below. This data will update automatically as any additional data is loaded.

The script used to perform the server-side processing for this table is shown below. Please note that this is just an example script using PHP. Server-side processing scripts can be written in any language, using the protocol described in the DataTables documentation.

Pipelining data to reduce Ajax calls for paging

Other examples

Basic initialisation

Advanced initialisation

Data sources

Language and Internationalisation

DateTime

Plug-ins

Styling

Layout

API

Ajax

Server-side

DataTables