When facing MySQL replication issues, follow these steps to diagnose and resolve problems effectively:

1. Check Replication Status

Run SHOW SLAVE STATUS\G to inspect critical metrics:

  • Last_Error: Identifies the last replication error
  • Seconds_Behind_Master: Shows replication lag
  • IO_Thread_Started: Confirms if I/O thread is active
  • SQL_Thread_Started: Verifies SQL thread operation

⚠️ If Seconds_Behind_Master is high, consider:

2. Common Errors & Solutions

  • Error 1201: Can't connect to MySQL server
    ⚠️ Check network connectivity and firewall rules.

    MySQL replication connection issue

  • Error 1062: Duplicate key error
    ⚠️ Verify if data conflicts exist between master and slave.
    Use mysqldump to restore slave from a consistent backup.

  • GTID Mismatch
    ⚠️ Ensure both servers use compatible GTID modes.
    Review GTID configuration details

3. Synchronization Tips

  • Stop slave: STOP SLAVE;
  • Reset slave: RESET SLAVE;
  • Start slave: START SLAVE;
  • Monitor with: SHOW PROCESSLIST\G

4. Advanced Debugging

  • Analyze binlog format (ROW vs STATEMENT)
  • Check server time zones with SELECT @@global.time_zone;
  • Enable verbose logging: SET GLOBAL log_slave_update=1;

For deeper insights, explore MySQL replication best practices to prevent common pitfalls.
🚨 Always back up data before performing replication resets!