PHP is a very popular scripting language, used on many popular sites across
the web. In this article, we hope to help you to improve the
performance of your PHP scripts with some changes that you can make
very quickly and painlessly. Please keep in mind that your own
performance gains may vary greatly, depending on which version of PHP
you are running, your web server environment, and the complexity of
your code.
Profile your code to pinpoint bottlenecks
Hoare’s dictum states that Premature optimization is the root of all evil,
an important thing to keep in mind when trying to make your web sites
faster. Before changing your code, you’ll need to determine what is
causing it to be slow. You may go through this guide, and many others
on optimizing PHP, when the issue might instead be database-related or
network-related. By profiling your PHP code, you can try to pinpoint bottlenecks.
Upgrade your version of PHP
The team of developers who maintain the PHP engine have made a number of
significant performance improvements over the years. If your web server
is still running an older version, such as PHP 3 or PHP 4, you may want
to investigate upgrading before you try to optimize your code.
- Migrating from PHP 4 to PHP 5.0.x
- Migrating from PHP 5.0.x to PHP 5.1.x
- Migrating from PHP 5.1.x to PHP 5.2.x
Use caching
Making use of a caching module, such as Memcache, or a templating system which supports caching, such as Smarty, can help to improve the performance of your website by caching database results and rendered pages.
Use output buffering
PHP uses a memory buffer to store all of the data that your script tries to
print. This buffer can make your pages seem slow, because your users
have to wait for the buffer to fill up before it sends them any data.
Fortunately, you can make some changes that will force PHP to flush the
output buffers sooner, and more often, making your site feel faster to
your users.
Don’t copy variables for no reason
Sometimes PHP novices attempt to make their code “cleaner” by copying predefined
variables to variables with shorter names before working with them.
What this actually results in is doubled memory consumption, and
therefore, slow scripts. In the following example, imagine if a
malicious user had inserted 512KB worth of characters into a textarea
field. This would result in 1MB of memory being used!
$description = strip_tags($_POST['description']);
echo $description;
There’s no reason to copy the variable above. You can simply do this operation inline and avoid the extra memory consumption:
echo strip_tags($_POST['description']);
Avoid doing SQL queries within a loop
A common mistake is placing a SQL query inside of a loop. This results in
multiple round trips to the database, and significantly slower scripts.
In the example below, you can change the loop to build a single SQL
query and insert all of your users at once.
foreach ($userList as $user) {
$query = ‘INSERT INTO users (first_name,last_name)
VALUES(“‘ . $user[‘first_name’] . ‘”, “‘ . $user[‘last_name’] . ‘”)’;
mysql_query($query);
}
Produces:
INSERT INTO users (first_name,last_name) VALUES("John", "Doe")
Instead of using a loop, you can combine the data into a single database query.
$userData = [];
foreach ($userList as $user) {
$userData[] = ‘(“‘ . $user[‘first_name’] . ‘”, “‘ . $user[‘last_name’] . ‘”)’;
}
$query = ‘INSERT INTO users (first_name,last_name) VALUES’ . implode(‘,’, $iserData);
mysql_query($query);Produces:
INSERT INTO users (first_name,last_name) VALUES("John", "Doe"),("Jane", "Doe")...
Use single-quotes for long strings
The PHP engine allows both single-quotes and double-quotes for string
variable encapsulation, but there are differences! Using double-quotes
for strings tells the PHP engine to read the string contents and look
for variables, and to replace them with their values. On long strings
which contain no variables, that can result in poor performance.
$output = "This is the content for a very long article
which is a few hundred lines long
and goes on and on and on
…
The End";
Changing the double-quotes to
single-quotes prevents the PHP engine from parsing this string in an
attempt to expand variables which, in this example, don’t exist:
$output = 'This is the content for a very long article
which is a few hundred lines long
and goes on and on and on
…
The End';
Use switch/case instead of if/else
Using switch/case statements rather than loose-typed if/else statements when
testing against a single variable results in better performance,
readability, and maintainability. It’s important to note that using
switch/case does a loose-comparison, and should be taken into consideration when being used.
if($_POST['action'] == 'add') {
addUser();
} elseif ($_POST[‘action’] == ‘delete’) {
deleteUser();
} elseif ($_POST[‘action’] == ‘edit’) {
editUser();
} else {
defaultAction();
}
Instead, you can use switch/case to test against the value of $_POST['action']:
switch($_POST['action']) {
case ‘add’:
addUser();
break;
case ‘delete’:
deleteUser();
break;
case ‘edit’:
editUser();
break;
default:
defaultAction();
break;
}
Additional resources
- PHP Memcache module
- Smarty templating engine
- PHP string type reference
- PHP switch statement reference
Author: Eric Higgins, Google Webmaster
Recommended experience: Beginner to intermediate PHP knowledge
Web Collections 
