APC, an Open Source PHP opcode Cache on Ubuntu Intrepid 8.10 using PECL and APT

PHP is interpreted, PHP code is parsed and translated to opcodes (primitive instructions — akin to assembly language — that the PHP engine executes directly) every time it executes. An opcode cache eliminates that rework, making PHP applications faster.

Of course, an opcode cache will not help your site if your bottleneck in not CPU or memory. For example, if your bottleneck is in the database, or disk, the opcode cache will not directly help. However, since scripts start and end faster than without one, you may experience less contention in some cases.

Among available free opcode caches, we have :

• APC: Alternative PHP Cache. A free opcode cache maintained by PHP code developers.

• eAccelerator, a free fork of the now abandoned Turck MMCache.

• XCache. A free project by lighttpd.

With several servers running Ubuntu 8.04.01 LTS, Apache 2.2.8 and PHP 5.2.4 I have found that neither eAccelerator nor XCache are stable. In a matter of a day or so, you will get segmentation faults in Apache 2. Well you can watch the segmentation faults in apache error log and put the server back on when that happens . But it’s kind of a pain , so I went for APC . On the contrary, APC — currently using 3.0.19 — is very stable and never experiences segmentation faults.

APC is maintained by core PHP developers, including Rasmus Lerdorf and others. APC does not utilize a disk cache, unlike both eAccelerator and Xcache (although it is configurable). Xcache is a viable option, specially if you find installing APC daunting.

But it’s important to note that APC can perform poorly if you don’t give it enough memory to cache all of the code that your site uses. So, changing APC to use 64 MB of shared memory instead of the default 30 MB should be all right. APC uses this memory to cache the parsed and tokenized scripts for later calls.

Now let’s install APC . This assumes you’ve already installed the default LAMP Stack in Ubuntu.

Open a terminal and type :

sudo apt-get install php-pear php5-dev apache2-prefork-dev build-essential && sudo pecl install apc && sudo apt-get remove php5-dev apache2-prefork-dev

Now let’s edit the configuration file of apc. On your command prompt type :

gksudo gedit /etc/php5/conf.d/apc.ini

add these settings to the file :

extension=apc.so
apc.apc.stat = 0
apc.include_once_override = 1
apc.shm_size = 64

and restart apache 2 :

sudo /etc/init.d/apache2 restart

Now, let’s test an application. Choose an application or two to test. You can use your own code . I used phpMyAdmin for the sample. I assume you’ve already installed phpMyAdmin.

Running a benchmark

The Apache HTTP Web server ships with a utility named ab, short for Apache HTTP server benchmarking tool. Use ab to automate a large number of requests for PHP pages.

The ab utility is simple to use: Provide a repeat count and a URL. The ab utility requests that URL many times over and returns statistics. Because APC is already enabled, the first benchmark will show performance with acceleration.

Before you run ab, point your browser to http://localhost/phpmyadmin/. Visiting this page once loads all the PHP code used to render the page into the cache. Now, run the benchmark shown below, iterating 100,000 times.

ab -n 100000 http://localhost/phpmyadmin/

Here is part of the output on my local :

Time taken for tests:   25.857 seconds
Complete requests:      100000
Failed requests:        0
Write errors:           0
Non-2xx responses:      100000
Total transferred:      64000000 bytes
HTML transferred:       35000000 bytes
Requests per second:    3867.47 [#/sec] (mean)
Time per request:       0.259 [ms] (mean)
Time per request:       0.259 [ms] (mean, across all concurrent requests)
Transfer rate:          2417.17 [Kbytes/sec] received

The statistics of interest are requests per second and the total time to complete all the tests. For the former, a higher value is better; for the latter, lower is better.

Now, disable APC by editing the apc.ini file :

gksudo gedit /etc/php5/conf.d/apc.ini

comment out all the lines :

;extension=apc.so
;apc.apc.stat = 0
;apc.include_once_override = 1
;apc.shm_size = 64

and restart apache 2 :

sudo /etc/init.d/apache2 restart

Now run the benchmarch again :

ab -n 100000 http://localhost/phpmyadmin/

here is the output on my local :

Concurrency Level:      1
Time taken for tests:   26.579 seconds
Complete requests:      100000
Failed requests:        0
Write errors:           0
Non-2xx responses:      100000
Total transferred:      64000000 bytes
HTML transferred:       35000000 bytes
Requests per second:    3762.32 [#/sec] (mean)
Time per request:       0.266 [ms] (mean)
Time per request:       0.266 [ms] (mean, across all concurrent requests)
Transfer rate:          2351.45 [Kbytes/sec] received

Here, with APC disabled, the number of requests per second fell, reflecting that the Apache server took longer for each request. The time to run the entire suite of tests climbed, as well.

Although this is a simple benchmark — the phpMyAdmin connection to the database could have been disabled to limit processing time to interpreting PHP alone — and not highly scientific, it does demonstrate what you can achieve with APC. For a tiny investment (and, thankfully, no need to recompile PHP or Apache), APC can yield a relatively large return. The more complex your code, the greater the possible benefits.

Installing a LAMP Stack on Ubuntu Using APT

This is to help people set-up and install a LAMP (Linux-Apache-MySQL-PHP) stack in Ubuntu, including Apache 2, PHP 5 and MySQL 5.0. You can actually do it with one line of commands but since that’s not the point, let’s go step by step.

Installing Apache 2

open up the Terminal and then type this line:

sudo apt-get install apache2 apache2-utils

To restart the server

sudo /etc/init.d/apache2 restart

By default when restarting you will get this warning :

apache2: Could not determine the server’s fully qualified domain name, using 127.0.0.1 for ServerName
You will have to edit the apache configuration located at : /etc/apache2/apache2.conf

gksudo gedit /etc/apache2/apache2.conf

then add

ServerName localhost

to the file and save, restart apache2

Browse to http://localhost , you should see displayed a text message “it works”

By default, your document root folder is located at : /var/www/ . Out of the box, you won’t have write permission to this folder, so first of all we need to change that by changing the ownership of the folder to your user.

At a terminal, do the following (replacing salimane with your login name):

sudo chown -R salimane /var/www

By default, Ubuntu’s Apache 2 will ignore the directives in your .htaccess files. To make .htaccess files work as expected, you need to edit the file /etc/apache2/sites-available/default (sometimes /etc/apache2/sites-available/000-default)
Look for a section that looks like this:

<Directory /var/www/>
Options Indexes FollowSymLinks MultiViews
AllowOverride None
Order allow,deny
allow from all
# Uncomment this directive is you want to see apache2's
# default start page (in /apache2-default) when you go to /
#RedirectMatch ^/$ /apache2-default/
</Directory>

You need to modify the line containing “AllowOverride None” to read “AllowOverride All”. This tells Apache that it’s okay to allow .htaccess files to over-ride previous directives.

You must reload Apache before this change will have an effect:

sudo /etc/init.d/apache2 reload

Installing MySQL Server

open up the Terminal and then type this line:

sudo apt-get install mysql-server

In order for other computers on your network to view the server you have created, you must first edit the “Bind Address”. Begin by opening up Terminal to edit the MySQL configuration file my.cnf .

gksudo gedit /etc/mysql/my.cnf

remove or comment out the line

bind-address = 127.0.0.1
and restart mysql server with :

sudo /etc/init.d/mysql restart

Installing PHP5

open up the Terminal and then type this line:

sudo apt-get install php5

Installing PHP5 module for apache2

open up the Terminal and then type this line:

sudo apt-get install libapache2-mod-php5

In order for PHP to work and be compatible with Apache we must restart it. Type the following code in Terminal to do this:

sudo /etc/init.d/apache2 restart

To ensure there are no issues with PHP let’s give it a quick test run. In the terminal copy/paste the following line:

echo "<?php phpinfo(); ?>" > /var/www/phpinfo.php

Now open your web browser and type the following into the web address: http://localhost/phpinfo.php

Installing MySQL module for PHP5

open up the Terminal and then type this line:

sudo apt-get install php5-mysql mysql-client

then edit the PHP configuration file php.ini and uncomment the following line by taking out the semicolon (;).
Change this line:

;extension=mysql.so

To look like this:

extension=mysql.so

Now just restart Apache and you are all set!

sudo /etc/init.d/apache2 restart

Installing PHPMyAdmin

One of the easiest ways to manage your new MySQL database server is to use the graphical tool PHPMyAdmin.
Simply go to your terminal again and enter the following command:

sudo apt-get install phpmyadmin libapache2-mod-auth-mysql

The phpmyadmin configuration file will be installed in: /etc/phpmyadmin
Now you will have to edit the apache config file by typing :

gksudo gedit /etc/apache2/apache2.conf

and include the following line:

Include /etc/phpmyadmin/apache.conf

Restart Apache :

sudo /etc/init.d/apache2 restart

Now just point your browser at http://localhost/phpmyadmin/.

Installing some useful modules in PHP

If you have installed xampp for Linux you will see that by default they are already some modules installed for you . But unfortunately for the default lamp stack in Ubuntu it’s not, so let’s install those common used modules in php like gd,pear,curl,memcache,xmlrpc,xsl…

sudo apt-get install php5-dev php5-gd php-pear php5-curl php5-memcache php5-xmlrpc php5-xsl php5-imagick php5-mcrypt php5-mhash

Restart Apache

sudo /etc/init.d/apache2 restart