使用Apache作为Web服务器，PHP在应用程序层和MongoDB处理大量的http请求

I have an API written in PHP with two very basic functionality as getUserData and UpdateUserData that interacts with MongoDB using MongoDB Driver 1.4.2 for PHP. We expect about 1500 requests per second (1000 for getUserData and about 500 for updateUserData). I have configured apache to handle maximum clients upto 1500 at the same time, making changes in the MPM configurations. When I test this setup using Jmeter, results are not very impressive considering the capability of MongoDB.

I think, MongoDB Driver is not making persistent connections as I can see more than 1300 connections open, after the test.How can I avoid this handshaking ? Can using nodejs instead of PHP be helpfull for me ?