Unix Sockets vs TCP/IP Sockets: Performance, Use Cases and MySQL Connection Optimization


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Unix sockets and TCP/IP sockets serve similar purposes but operate at different layers with distinct characteristics:


// TCP/IP socket connection example in Python
import socket
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)  # IPv4 TCP socket
s.connect(('127.0.0.1', 3306))

# Unix domain socket example
us = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
us.connect('/var/run/mysqld/mysqld.sock')

Unix sockets typically offer better performance for local communication:

  • No network protocol overhead (TCP handshake, congestion control, etc.)
  • Bypasses the entire network stack
  • Lower latency (typically 30-50% faster for local connections)

When connecting to MySQL with "localhost" as the host:


// PHP PDO using Unix socket (implicit)
$dbh = new PDO('mysql:dbname=testdb;host=localhost', $user, $pass);

// Explicit TCP/IP connection
$dbh = new PDO('mysql:dbname=testdb;host=127.0.0.1;port=3306', $user, $pass);

Use Unix sockets when:

  • Client and server are on the same machine
  • Maximum performance is needed
  • No network security concerns (since it's local)

Use TCP/IP sockets when:

  • Communicating across machines
  • Need standard port-based access control
  • Require network-level encryption (SSL/TLS)

Sample benchmark results for 10,000 simple MySQL queries:

TCP/IP localhost: 1.82 seconds
Unix socket: 1.12 seconds
Network TCP (remote): 3.45 seconds

For MySQL specifically, the socket path can be configured in my.cnf:


[mysqld]
socket=/var/run/mysqld/mysqld.sock

[client]
socket=/var/run/mysqld/mysqld.sock

Remember that some MySQL client libraries may behave differently across programming languages when handling "localhost" versus "127.0.0.1".

When working with database connections in Unix-like systems, you'll encounter two primary socket types:


// TCP/IP socket connection example (MySQL)
$dsn = 'mysql:host=127.0.0.1;port=3306;dbname=test';
$user = 'username';
$password = 'password';

// Unix domain socket connection example (MySQL)
$dsn = 'mysql:unix_socket=/var/run/mysqld/mysqld.sock;dbname=test';

Unix domain sockets (UDS) typically offer better performance for local communication:

  • No network protocol overhead
  • No TCP handshakes or connection teardowns
  • Kernel handles data copying between processes directly

Unix sockets provide filesystem-based permissions:


$ ls -l /var/run/mysqld/mysqld.sock
srwxrwxrwx 1 mysql mysql 0 Aug 10 10:00 /var/run/mysqld/mysqld.sock

While TCP/IP connections require additional security measures like firewalls and encrypted tunnels.

Use Unix sockets when:

  • Client and server are on the same machine
  • You need maximum performance
  • Filesystem permissions provide sufficient security

Use TCP/IP sockets when:

  • Communicating across machines
  • Need network-level features (load balancing, failover)
  • Working with containers where socket files might not persist

For PostgreSQL:


# TCP/IP connection
host    all             all             127.0.0.1/32            md5

# Unix socket connection
local   all             all                                     peer

For Redis:


# TCP configuration
bind 127.0.0.1
port 6379

# Unix socket configuration
unixsocket /tmp/redis.sock
unixsocketperm 770

Common issues with Unix sockets:


# Check if socket exists
test -S /path/to/socket.sock || echo "Socket missing"

# Verify permissions
stat -c "%A %U %G" /path/to/socket.sock

For TCP connections, standard network tools apply:


telnet 127.0.0.1 3306
netstat -tulnp | grep mysql