PHP is suddenly super slow

Question

I'm working on a web application using PHP, Apache, and MySQL. For the past year the response times of this application have been good. Suddenly yesterday the application became very slow on Firefox (complete page load, including CSS and JavaScript files: around 20 seconds. During page load, Firefox is completely unusable). Interestingly the response times in Internet Explorer were a bit slower (around 2 seconds instead of <1 second).

The strange thing is: The application worked fine two days ago and out of nowhere became very slow. I didn't change anything in the sourcecode. I didn't change a thing in php.ini or httpd.conf. I already log the response times of PHP functions, and that performance hasn't changed.

At first I thought it had something to do with Firefox, so I completely removed Firefox, restarted Windows Vista and did a clean install of Firefox (without extensions). No result.

After testing several things I found out that when I copy the application data to another folder in my document root, the application works fine again. Problem is solved you could think, but it's very annoying that I now have to use another URL and (more important) I don't get it. Why is my application very very very slow in one folder and perfectly fine in another folder?

Does it have something to do with Firefox or with Apache? The name of the folder in which the application is very slow does not appear in either php.ini or httpd.conf.

Answer 1

Some suggestions:

1. Install Fiddler on the client. This will allow you to analyse the low-level HTTP traffic coming from the server.

2. Extract some of the queries from your PHP code and run them interactively in the MySQL client and see if they're running slowly.

3. Log into the server (or get a system administrator if you don't have access) and run the Task Manager (Windows) or top (Unix) and make sure there's nothing else hogging the server. If you haven't changed anything, maybe something else has changed on the server. Also, check the server logs/ Event Viewer.

4. There is a Zend extension called APD that you can install on the server (again, assuming you have rights), and it will profile your PHP code and write out a file showing what functions are being called by your PHP scripts are how long PHP is spending in each function.

Answer 2

Look for areas that might cause blocking, like shelling out to curl or opening a file over NFS in the code. If the remove system is timing out, it will drastically affect Apache performance as each request ties up the server for however many seconds it takes to time out and fail the lagging request.