For those confuse about the memcached extension and the memcache extension, the short story is that both of them are clients of memcached server, and the memcached extension offer more features than the memcache extension.

GOTCHA: Recently I was tasked with moving from PECL memcache to PECL memcached and ran into a major problem -- memcache and memcached serialize data differently, meaning that data written with one library can't necessarily be read with the other library.

For example, If you write an object or an array with memcache, it's interpreted as an integer by memcached.  If you write it with memcached, it's interpreted as a string by memcache.

tl;dr - You can't safely switch between memcache and memcached without a either a cache flush or isolated cache environments.

<?php
$memcache = new Memcache;
$memcacheD = new Memcached;
$memcache->addServer($host);
$memcacheD->addServers($servers);

$checks = array(
    123,
    4542.32,
    'a string',
    true,
    array(123, 'string'),
    (object)array('key1' => 'value1'),
);
foreach ($checks as $i => $value) {
    print "Checking WRITE with Memcache\n";
    $key = 'cachetest' . $i;
    $memcache->set($key, $value);
    usleep(100);
    $val = $memcache->get($key);
    $valD = $memcacheD->get($key);
    if ($val !== $valD) {
        print "Not compatible!";
        var_dump(compact('val', 'valD'));
    }

    print "Checking WRITE with MemcacheD\n";
    $key = 'cachetest' . $i;
    $memcacheD->set($key, $value);
    usleep(100);
    $val = $memcache->get($key);
    $valD = $memcacheD->get($key);
    if ($val !== $valD) {
        print "Not compatible!";
        var_dump(compact('val', 'valD'));
    }
}

## Installing Memcached on Ubuntu

To install Memcached on Ubuntu, go to terminal and type the following commands −

$sudo apt-get update
$sudo apt-get install memcached

## Confirming Memcached Installation

To confirm if Memcached is installed or not, you need to run the command given below. This command shows that Memcached is running on the default port 11211.

$ps aux | grep memcached

To run Memcached server on a different port, execute the command given below. This command starts the server on the TCP port 11111 and listens on the UDP port 11111 as a daemon process.

$memcached -p 11111 -U 11111 -u user -d

You can run multiple instances of Memcached server through a single installation.

The module also supports SASL authentication, it just isn't documented sadly. You'll need to run the following code:

<?php
$m = new Memcached();
$m->setOption(Memcached::OPT_BINARY_PROTOCOL, true);
$m->setSaslAuthData("user-1", "pass");
?>

You need to enable the "memcached.use_sasl = 1" ini option for memcached in the php.ini file.