Best practices for optimizing LAMP sites for speed?
I want to know when building a typical site on the LAMP stack how do you optimize it for the best possible load times. I am picturing a typical DB-driven site.
This is a high-level look and could probably pull in question and let me break it down into each layer of the stack.
L - At the system level, (setup and filesystem) can you do to improve speed? One thing I can think of is image sizes, can compression here help optimize anything?
A - There have to be a ton of settings related to site speed here in the web server. Not my Forte. Probably depends a lot on how many sites are running concurrently.
M - MySQL in a database driven site, DB performance is key. Is there a better normalization approach i.e, using link tables? Web developers often just make simple monolithic tables resembling 1NF and this can kill performance.
P - aside from performance-boosting settings like caching, what can the programmer do to affect performance at a high level? I would really like to know if MVC design approaches hit performance more than quick-and-dirty. Other simple tips like are sessions faster than cookies would be interesting to know.
Obviously you have to get down and dirty into the details and find what code is slowing you down. Also I realize that many sites have many different performance characteristics, but let's assume a typical site that has more reads then writes.
I am just wondering if we can compile a bunch of best practices and fully expect people to link other questions so we can effectively workup a checklist.
My goal is to see if even in addition to the usual issues in performance we can see some oddball things you might not think of crop up to go along with a best-practices summary.
So my question is, if you were starting from scratch, how would you make sure your LAMP site was fast?
Answer
Here's a few personal must-dos that I always set up in my LAMP applications.
Install mod_deflate for apache, and do not use PHP's gzip handlers. mod_deflate will allow you to compress static content, like javascript/css/static html, as well as the usual dynamic PHP output, and it's one less thing you have to worry about in your code.
Be careful with .htaccess files! Enabling .htaccess files for directories in your app means that Apache has to scan the filesystem constantly, looking for .htaccess directives. It is far better to put directives inside the main configuration or a vhost configuration, where they are loaded once. Any time you can get rid of a directory-level access file by moving it into a main configuration file, you save disk access time.
Prepare your application's database layer to utilize a connection manager of some sort (I use a Singleton for most applications). It's not very hard to do, and reducing the number of database connections your application opens saves resources.
If you think your application will see significant load, memcached can perform miracles. Keep this in mind while you write your code... perhaps one day instead of creating objects on the fly, you will be getting them from memcached. A little foresight will make implementation painless.
Once your app is up and running, set MySQL's slow query time to a small number and monitor the slow query log diligently. This will show you where your problem queries are coming from, and allow you to optimize your queries and indexes before they become a problem.
For serious performance tweakers, you will want to compile PHP from source. Installing from a package installs a lot of libraries that you may never use. Since PHP environments are loaded into every instance of an Apache thread, even a 5MB memory overhead from extra libraries quickly becomes 250MB of lost memory when there's 50 Apache threads in existence. I keep a list of my standard ./configure line I use when building PHP here, and I find it suits most of my applications. The downside is that if you end up needing a library, you have to recompile PHP to get it. Analyze your code and test it in a devel environment to make sure you have everything you need.
Minify your Javascript.
Be prepared to move static content, such as images and video, to a non-dynamic web server. Write your code so that any URLs for images and video are easily configured to point to another server in the future. A web server optimized for static content can easily serve tens or even hundreds of times faster than a dynamic content server.
That's what I can think of off the top of my head. Googling around for PHP best practices will find a lot of tips on how to write faster/better code as well (Such as: echo is faster than print).