Troubleshoot and Reset MySQL/MariaDB Replication – ‘Could not find first log file name in binary log index file’

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If you are getting an error below in your MySQL or MariaDB replication, then there is possibility that replication has been broken due to multiple reasons e.g. corrupted file disk, synchronisation issues etc.

Got fatal error 1236 from master when reading data from binary log: ‘Could not find first log file name in binary log index file’

In order to restore back the replication on slave server, the best possible way is to reset the slave server and then start it again by providing master server bin log file index and position. Below is a step by step guide to show this.

How to Reset Slave in MySQL/MariaDB Replication

MySQL replication is a powerful feature for creating copies of databases across multiple servers, ensuring high availability and disaster recovery. However, there are instances when you might need to reset the slave server—perhaps due to misconfiguration, changes in the replication setup, or troubleshooting issues. This guide walks you through the steps to reset a slave in MySQL replication safely and effectively.

Why Reset a Slave in MySQL Replication?

Resetting the slave server may be necessary in several scenarios:

• To reconfigure the replication process.
• To fix synchronization issues.
• To remove old or corrupted replication settings.

Let’s dive into the step-by-step process.

Steps to Reset Slave in MySQL Replication

1. Stop the Slave

Before making any changes, login into your mysql server as a root and stop the slave replication process:

STOP SLAVE;

This ensures no data is being processed while resetting.

2. Reset the Slave

To clear the replication configuration, use the RESET SLAVE command:

• To reset the replication and remove the binary log files used for replication: RESET SLAVE;
• To remove replication configuration files (e.g., master.info and relay-log.info): RESET SLAVE ALL;

3. Verify the Reset

After resetting, check the status to ensure the slave has been cleared:

SHOW SLAVE STATUS\G;

The output should show empty fields, indicating the reset was successful.

4. Reconfigure the Slave

If you need to re-establish replication, follow these steps:

1. Login into your master server’s MySQL as a root and run the following command.

SHOW MASTER STATUS\G;

This will output current log file status and position of the master server. You should not these down:

2. Note down File and Position and run the following command by replacing the file and position values shown in the above screenshot:

Option 1: If you have run RESET SLAVE ALL; command then all the master configurations would have been removed from your slave server. In this case you’ll need to run the following command providing: MASTER_HOST, MASTER_USER, MASTER_PASSWORD, MASTER_LOG_FILE, MASTER_LOG_POS

CHANGE MASTER TO MASTER_HOST='master_host', MASTER_USER='replication_user', MASTER_PASSWORD='replication_password', MASTER_LOG_FILE='master_log_file', MASTER_LOG_POS=master_log_position;

Option 2: If you have run RESET SLAVE; command then previous master configurations would still be retained in your slave server. In this case you’ll need to run the following command:

CHANGE MASTER TO MASTER_LOG_FILE='master_log_file', MASTER_LOG_POS=master_log_position;

3. Start the Slave:

START SLAVE;

4. Verify Replication:

SHOW SLAVE STATUS\G;

Check for fields like Slave_IO_Running and Slave_SQL_Running, which should show Yes.

Important Considerations

• Backup Your Data: Before resetting the slave, ensure you have backups to avoid data loss.
• Permissions: Ensure you have the necessary privileges to execute replication commands.
• Test in a Staging Environment: If possible, test the process in a non-production environment to minimize risk.

Conclusion

Resetting a slave in MySQL replication is a straightforward process but must be done with caution. By following the steps outlined in this guide, you can safely reset and reconfigure your replication setup, ensuring smooth operation and data consistency.