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).
