Set up memcached on CentOS

This section provides instructions to install memcached on CentOS. For additional information, consult the memcached wiki.

Because PHP has no native support for memcache, you must install an extension for PHP to use it. There are two PHP extensions available and it is important to decode which to use:

Install and configure memcached on CentOS

To install memcached on CentOS, perform the following tasks as a user with root privileges:

Verify memcached works before installing Commerce

Adobe recommends testing memcached to make sure it works before you install Commerce. Doing so takes only a few minutes and can simplify troubleshooting later.

Verify memcached is recognized by the web server

To verify memcached is recognized by the web server:

Verify you are using memcached version 3.0.5 or later.

If memcache does not display, restart the web server and refresh the browser page. If it still does not display, verify you installed the php-pecl-memcache extension.

Create a memcache test consisting of a MySQL database and PHP script

The test uses a MySQL database, table, and data to verify you can retrieve the database data and store it in memcache. A PHP script first searches the cache. If the result does not exist, the script queries database. After the query has been fulfilled by the original database, the script stores the result in memcache, using the set command.

More details about this test

Create the MySQL database:

mysql -u root -p

At the mysql prompt, enter the following commands:

create database memcache_test;
GRANT ALL ON memcache_test.* TO memcache_test@localhost IDENTIFIED BY 'memcache_test';
use memcache_test;
create table example (id int, name varchar(30));
insert into example values (1, "new_data");
exit

Create cache-test.php in your web server’s docroot:

$meminstance = new Memcached();

$meminstance->addServer('<memcached hostname or ip>', <memcached port>);

$query = "select id from example where name = 'new_data'";
$querykey = "KEY" . md5($query);

$result = $meminstance->get($querykey);

if (!$result) {
   try {
        $dbh = new PDO('mysql:host=localhost;dbname=memcache_test','memcache_test','memcache_test');
        $dbh->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
        $result = $dbh->query("select id from example where name = 'new_data'")->fetch();
        $meminstance->set($querykey, $result, 0, 600);
        print "got result from mysql\n";
        return 0;
    } catch (PDOException $e) {
        die($e->getMessage());
    }
}
print "got result from memcached\n";
return 0;

Where <memcached hostname or ip> is either localhost, 127.0.0.1, or the memcache hostname or IP address. The <memcached port> is the listen port; by default, 11211.

Run the script from the command line.

cd <web server docroot>

php cache-test.php

The first result is got result from mysql. This means that the key did not exist in memcached but it was retrieved from MySQL.

The second result is got result from memcached, which verifies that the value is stored successfully in memcached.

Finally, you can view the memcache keys using Telnet:

telnet localhost <memcache port>

At the prompt, enter

stats items

The result is similar to the following:

STAT items:3:number 1
STAT items:3:age 1075
STAT items:3:evicted 0
STAT items:3:evicted_nonzero 0
STAT items:3:evicted_time 0
STAT items:3:outofmemory 0
STAT items:3:tailrepairs 0

Flush the memcache storage and quit Telnet:

flush_all

quit

Additional information about the Telnet test