Troubleshooting MySQL Error 1189: Network Errors with Master Server

When working with MySQL replication, you might encounter Error 1189, which is associated with SQLSTATE 08S01 and the message “Net error reading from master.” This error indicates that a network issue occurred while a slave server was trying to read data from the master server. Properly addressing this error is crucial for ensuring data consistency and replication reliability. Let’s go through how to understand, diagnose, and fix this replication-related network error.

Understanding Error 1189

Error 1189 occurs during replication when a slave server is unable to read data from the master server over the network. This can be due to a variety of network-related issues, such as connectivity problems, timeouts, or configuration errors.

Diagnosing the Issue

To diagnose Error 1189, follow these steps:

  1. Check Network Connectivity: Ensure that the slave can reach the master server over the network. Simple tools like ping or traceroute can help determine network reachability.
  2. Review Error Logs: MySQL error logs on both the master and slave servers may contain additional details about the network error. Look for messages that occurred around the same time as the replication error.
  3. Examine Replication Status: Use the SHOW SLAVE STATUS\G command on the slave server to get detailed information about the replication process and any errors.
  4. Check Configuration Settings: Verify that the replication-related settings, such as master_host, master_port, master_user, and master_password, are correctly configured on the slave server.

Fixing Error 1189

After diagnosing the problem, here are some ways to resolve it:

  1. Resolve Network Issues: If the problem is due to network connectivity, work with your network administrator to resolve any underlying network issues.
  2. Increase Timeouts: Network glitches can cause timeouts. You can increase the net_read_timeout and net_write_timeout settings on both the master and slave servers to give more time for operations to complete: SET GLOBAL net_read_timeout=120; SET GLOBAL net_write_timeout=120;
  3. Adjust Slave Settings: If the error is due to incorrect replication settings on the slave, update them with the correct values: CHANGE MASTER TO MASTER_HOST='master_host_name', MASTER_USER='replication_user_name', MASTER_PASSWORD='replication_password', MASTER_PORT=master_port_number;
  4. Verify Master Server Load: A heavily loaded master server can lead to replication delays and network timeouts. Monitor the master server’s performance and optimize it to handle the replication workload.
  5. Reconfigure Replication: If the issue persists, consider reconfiguring replication from scratch. This involves resetting the slave, ensuring that the master has binary logging enabled with the correct format, and setting up the slave with the correct coordinates: STOP SLAVE; RESET SLAVE; CHANGE MASTER TO MASTER_LOG_FILE='recorded_log_file_name', MASTER_LOG_POS=recorded_log_position; START SLAVE;
  6. Check for Firewall Issues: Ensure that any firewalls between the master and slave servers are configured to allow traffic on the MySQL replication port (default is 3306).

By methodically diagnosing network issues and adjusting configurations as needed, you can resolve Error 1189 and restore stable replication between your MySQL servers. Always remember to perform such troubleshooting steps during maintenance windows or periods of low traffic to minimize the impact on your production environment.

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