JavaServlet vs PHP

I & my team are building an professionnal B2B website basically based on Apache/PHP/MySQL/Linux.

For the moment, we are in a very standard hardware architecture with apache php in front, firewall then mySQL database in a dmz.

I have to build an alert system (mail + online warning) and this system has to scan a lot database for matching & user preferences.

As I don't want to overload my front apache/Php servers I think we'll build a cgi server in the dmz to handle all alerts.
My question is:

will I use a php server in the dmz or a java servlet?
I don't know if php could offer me the same advantages.

Thanks for help or comments

The topic "PHP versus JSP" has been discussed in several articles and the php-general malinglist:

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Online Articles
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IBM: Choosing the right server-side scripting language
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IBM: JSP technology -- friend or foe?
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ZDNet: Four scripting languages speed development
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Webmonkey: Server-Side Scripting Shootout
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PHP Every Where: What is Wrong With Java Server Pages
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Servlets.com: The Problems with JSP
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Threads in PHP-General Malinglist
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When I read the above discussions, I was honestly surprised how powerful PHP is ;-)

Sandro