Jaslabs: High performance Software

By Justin Silverton

XMLHttpRequest, the main component behind AJAX, does not automatically work across multiple domains. This means that you cannot make a request to an ovject on a domain that is different from the web page’s domain. There is an easy solution to this issue: apache’s mod_rewrite module.

Example

function getXMLHttpObject()
{
if (window.XMLHTTPRequest)
return new XMLHttpRequest();
else if (window.ActiveXObject)
return new ActiveXObject("Microsoft.XMLHTTP");
else
return null;
}

http.open("POST"."http://www.yahoo.com/service");
http.onreadystatechange = handleHttpResponse;

The above example will fail with both Firefox and Internet Explorer (unless you are running it on a web page located on the yahoo domain). There are other ways to allow cross site ajax. Within Internet Exporer, the default security settings can be changed or a host can be added to the “trusted hosts” list. Firefox, on the other hand, has a concept called signed scripts. Both of these methods will not work for most websites on the Internet. This is because it would involve every user coming to your site adding your page to their trusted host list.

Apache setup

1. Install apache with both mod_rewrite and proxy enabled.
2. Create the following rule: RewriteRule ^/yahoo_proxy http://www.yahoo.com/service [P]

Note: The [P] indicates a pass-through proxy.

Replace the above line: (http.open("POST"."http://www.yahoo.com/service")) with

http.open("POST"."http://your_host/yahoo_proxy") and a connection will be made to the yahoo domains through your apache server while not violating the security restrictions of IE or Firefox.

By Justin Silverton

A French Translation can be found here: http://www.vecteur-renaissance.com/vhoen/index.php/2006/04/15/27-10-conseils-pour-accelerer-des-scripts-php

1. A PHP script will be served at least 5-10 times slower than a static HTML page by Apache. Try to use more static HTML pages and fewer scripts. 
2. Enable the compression of HTML by putting in your php.ini:output_handler = ob_gzhandler 
3. Install a PHP caching suite. I have personally used zend (commercial), turck mmcache, and ioncube, and they all work very well. 
4. Switch from file based sessions to shared memory sessions. Compile PHP with the –with-mm option and set session.save_handler=mm in php.ini. This can drastically improve session management performance.
5. Another caching technique that can be used when you have pages that don’t change too often is to cache the HTML output of your PHP pages. (a list of template solutions is posted within one of my previous articles).
6. Use output buffering (See ob_start). This will speed up your PHP code by 5-15% if you frequently print or echo in your code. 
7. On Windows, FastCGI is the highest performance way of running PHP with Apache. 
8. In PHP4, objects and arrays should be passed to functions by reference (with &), and everything else by value. In PHP5, objects are already passed by reference.
9. Don’t use images when text will do. Reduce your image sizes with a software like MacroMedia Fireworks or imagemagick. 
10. If possible, Run your database server on a different machine. If all static content is served from another server, then you can turn off KeepAlives in httpd.conf to speed up client disconnects. 

Apache is available on both Unix and Windows. It is the most popular web server in the world. Apache 1.3 uses a pre-forking model for web serving. When Apache starts up, it creates multiple child processes that handle HTTP requests. The initial parent process acts like a guardian angel, making sure that all the child processes are working properly and coordinating everything. As more HTTP requests come in, more child processes are spawned to process them. As the HTTP requests slow down, the parent will kill the idle child processes, freeing up resources for other processes. The beauty of this scheme is that it makes Apache extremely robust. Even if a child process crashes, the parent and the other child processes are insulated from the crashing child.
The pre-forking model is not as fast as some other possible designs, but to me that it is “much ado about nothing” on a server serving PHP scripts because other bottlenecks will kick in long before Apache performance issues become significant. The robustness and reliability of Apache is more important.

Apache 2.0 offers operation in multi-threaded mode. My benchmarks indicate there is little performance advantage in this mode. Also be warned that many PHP extensions are not compatible (e.g. GD and IMAP). Tested with Apache 2.0.47.
Apache is configured using the httpd.conf file. The following parameters are particularly important in configuring child processes:

MaxClients : default: 256
The maximum number of child processes to create. The default means that up to 256 HTTP requests can be handled concurrently. Any further connection requests are queued.

StartServers: default: 5
The number of child processes to create on startup.