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Replication Problems

Troubleshooting MySQL/MariaDB replication issues.

IO Thread Stopped​

Symptoms: "Slave_IO_Running: No" in replication status.

Common Causes:

  • Master hostname changed
  • Network connectivity issues
  • Master MySQL not running
  • Authentication failed

Solutions:

# On slave, check error:
mysql -e "SHOW SLAVE STATUS\G" | grep Last_IO_Error

# If hostname changed, update master info:
mysql -e "STOP SLAVE; CHANGE MASTER TO MASTER_HOST='new-hostname'; START SLAVE;"

SQL Thread Stopped​

Symptoms: "Slave_SQL_Running: No" in replication status.

Common Causes:

  • Duplicate key error
  • Schema mismatch
  • Disk full

Solutions:

# Check error:
mysql -e "SHOW SLAVE STATUS\G" | grep Last_SQL_Error

# Skip one error (use cautiously):
mysql -e "STOP SLAVE; SET GLOBAL SQL_SLAVE_SKIP_COUNTER = 1; START SLAVE;"

High Replication Lag​

Symptoms: Seconds_Behind_Master growing continuously.

Common Causes:

  • Slave server overloaded
  • Slow queries on master
  • Network bandwidth issues

Solutions:

  1. Check slave CPU/memory usage
  2. Identify slow queries: SHOW PROCESSLIST;
  3. Consider upgrading slave hardware