When working with Memcached on Debian systems, using Unix domain sockets instead of TCP/IP can provide noticeable performance improvements. The key benefits include:

• Eliminates TCP/IP stack overhead
• Reduces context switching between kernel and user space
• Provides lower latency communication
• Improves security by restricting access to local processes

Here's the proper way to configure Memcached to use Unix sockets on Debian:

# First, stop the running memcached service
sudo systemctl stop memcached

# Edit the configuration file
sudo nano /etc/memcached.conf

Make these changes to your configuration file:

# Disable TCP/IP listening
#-p 11211
#-l 127.0.0.1

# Enable Unix socket
-s /var/run/memcached/memcached.sock
-a 0766

# Recommended additional parameters
-m 64       # Memory allocation in MB
-u memcache # Run as memcache user
-c 1024     # Maximum simultaneous connections

Proper permissions are crucial for Unix socket operation:

# Create directory for socket
sudo mkdir -p /var/run/memcached
sudo chown memcache:memcache /var/run/memcached

# Set correct permissions
sudo chmod 755 /var/run/memcached

For Drupal sites, update your settings.php file with the socket connection:

$settings['memcache']['servers'] = ['unix:///var/run/memcached/memcached.sock' => 'default'];
$settings['memcache']['options'] = [
  'binary_protocol' => TRUE,
  'connect_timeout' => 100,
];

If you encounter internal server errors, check these aspects:

# Verify socket creation
ls -la /var/run/memcached/memcached.sock

# Check memcached logs
journalctl -u memcached --no-pager -n 50

# Test socket connectivity
nc -U /var/run/memcached/memcached.sock

In my tests on a Debian 10 server with Drupal 9, the performance gains were:

For high-traffic sites, consider these additional optimizations:

# In /etc/memcached.conf
-I 1m       # Increase slab page size
-o modern   # Enable modern protocol
-t 4        # Worker threads (match CPU cores)
-R 20       # Max requests per event

Use these commands to monitor your socket-based Memcached instance:

# Check socket statistics
ss -x -a | grep memcached

# Get memory usage details
echo "stats slabs" | nc -U /var/run/memcached/memcached.sock

# Monitor active connections
echo "stats items" | nc -U /var/run/memcached/memcached.sock

When configuring Memcached on Debian systems, using Unix domain sockets instead of TCP/IP can provide measurable performance improvements by eliminating network stack overhead. Benchmarks typically show 10-15% faster operations for local connections, though actual gains depend on your workload characteristics.

Here's the complete process for Debian/Ubuntu systems:

# Create socket directory
sudo mkdir -p /var/run/memcached
sudo chown memcache:memcache /var/run/memcached

# Edit /etc/memcached.conf:
-s /var/run/memcached/memcached.sock
-a 0766

# Comment out TCP/IP lines:
# -p 11211
# -l 127.0.0.1

The most common issue is improper socket permissions. The socket must be accessible to both Memcached and your web server user (typically www-data). Add these commands after configuration:

sudo usermod -a -G memcache www-data
sudo systemctl restart memcached apache2

Verify the socket is active and accessible:

sudo netstat -a -p --unix | grep memcached
sudo -u www-data stat /var/run/memcached/memcached.sock

For Drupal sites, update your settings.php with the socket path:

$conf['memcache_servers'] = array(
  'unix:///var/run/memcached/memcached.sock' => 'default'
);

While Unix sockets reduce latency, the actual impact depends on:

• Connection frequency (more benefit for high churn)
• Average object size (greater benefit for smaller items)
• System load (more noticeable under heavy traffic)

If encountering 500 errors after the switch:

1. Verify memcached.sock exists and has 0766 permissions
2. Check system logs: journalctl -u memcached
3. Test connectivity: memcstat --servers=/var/run/memcached/memcached.sock