The fundamental distinction lies in the communication mechanism. MySQL sockets (Unix domain sockets) use filesystem communication, while TCP/IP connections (host:port) utilize network protocols. This creates several technical implications:

# Socket connection example (PHP)
$link = mysqli_connect('localhost:/var/run/mysqld/mysqld.sock', 'user', 'password');

# TCP/IP connection example
$link = mysqli_connect('127.0.0.1:3306', 'user', 'password');

Unix domain sockets generally show 10-20% better throughput for local connections. Here's why:

• No TCP overhead (handshakes, congestion control)
• No network stack processing
• Direct kernel-to-kernel communication

Consider sockets mandatory when:

1. MySQL is configured with skip-networking
2. Running in containerized environments with shared volumes
3. High-security environments restricting network access

Host:port connections become necessary when:

# Remote connection must use TCP
$link = mysqli_connect('db.example.com:3306', 'user', 'password');

Additional benefits include:

• Standardized port configuration (3306)
• Easier container linking
• Compatible with all MySQL clients

MySQL's my.cnf settings for socket optimization:

[mysqld]
socket = /var/run/mysqld/mysqld.sock
skip-networking # Optional for security

Connection pooling comparison:

# Socket-based pool (Python)
pool = QueuePool(
    lambda: create_engine('mysql+pymysql://user:pass@/dbname?unix_socket=/tmp/mysql.sock')
)

# TCP pool
pool = QueuePool(
    lambda: create_engine('mysql+pymysql://user:pass@localhost:3306/dbname')
)

Common socket issues and fixes:

# Check socket permissions
ls -la /var/run/mysqld/mysqld.sock

# Verify socket location
mysqladmin variables | grep socket

# Alternative connection test
mysql --socket=/path/to/mysql.sock -u user -p

Remember that some cloud providers modify default socket behaviors, so always check your specific environment.

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When connecting to MySQL, you essentially have two pathways:

• Unix domain socket (e.g., /var/run/mysqld/mysqld.sock)
• TCP/IP connection (e.g., localhost:3306 or 127.0.0.1:3306)

Unix sockets are inter-process communication (IPC) mechanisms that only work when:

# Typical socket connection in PHP
$db = new mysqli('localhost', 'user', 'password', 'database', null, '/var/run/mysqld/mysqld.sock');

Key advantages:

• No network stack overhead - Data never leaves the machine
• Filesystem permissions - Additional security layer via socket file permissions
• No port conflicts - Doesn't consume a TCP port

# Standard TCP connection in Python
import mysql.connector
db = mysql.connector.connect(
    host="127.0.0.1",
    port=3306,
    user="user",
    password="password",
    database="db"
)

When you must use TCP:

• Remote database servers
• Containerized environments (Docker-to-Docker communication)
• When your app and DB are on separate machines

For local connections, benchmarks typically show:

Metric	Unix Socket	TCP Localhost
Latency	15-20% lower	Higher
Throughput	10-15% better	Lower

Sockets provide:

• Filesystem-based access control
• No exposure to network sniffing
• Cannot be reached from external machines

TCP connections require:

• Proper firewall rules
• Secure authentication
• Potential SSL/TLS overhead

MySQL my.cnf settings:

[mysqld]
socket=/var/run/mysqld/mysqld.sock
port=3306

Connecting via socket in different languages:

// Node.js
const mysql = require('mysql');
const connection = mysql.createConnection({
  socketPath: '/var/run/mysqld/mysqld.sock',
  user: 'db_user',
  password: 'db_password',
  database: 'db_name'
});

Use sockets when:

• Application and DB are on same physical host
• Maximum local performance is critical
• Network security is a concern

Use TCP when:

• Connecting to remote databases
• In containerized environments (even if on same host)
• When socket file location is non-standard or inaccessible

Common socket errors:

ERROR 2002 (HY000): Can't connect to local MySQL server through socket

Solutions:

1. Verify socket path in my.cnf
2. Check file permissions (ls -l /var/run/mysqld/)
3. Confirm mysqld is running

TCP connection issues:

ERROR 2003 (HY000): Can't connect to MySQL server on 'host' (111)

Solutions:

1. Check if port 3306 is open (telnet host 3306)
2. Verify MySQL is listening (netstat -tulpn | grep 3306)
3. Check firewall rules