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Description

MySQL Error 2023 occurs when the database server encounters an issue while attempting to execute the `SHOW SLAVE HOSTS` command. This command is used in a replication setup to list all registered slave servers connected to the current master. The error indicates that the master server was unable to retrieve or present this information, often pointing to configuration, network, or internal server state problems.

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Error Message

Error on SHOW SLAVE HOSTS:

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Known Causes

3 known causes

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Incorrect Slave Reporting Configuration

Slave servers are not correctly configured with `report_host` and `report_port` settings in their `my.cnf` file, preventing them from registering their presence with the master.

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Master Server Resource Exhaustion

The master server might be under heavy load, experiencing high CPU, memory, or I/O utilization, which prevents it from properly processing the `SHOW SLAVE HOSTS` command.

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Network or Firewall Restrictions

Network connectivity issues or firewall rules (e.g., iptables, security groups) might be blocking communication pathways that the master server uses to gather or verify slave host information.

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Solutions

4 solutions available

1. Verify Slave Configuration and Status easy

Ensure the replication slave is properly configured and actively running.

1

Connect to your MySQL replication slave server using a MySQL client.

mysql -u your_user -p

2

Check the status of the slave threads.

SHOW SLAVE STATUS\G

3

Look for 'Slave_IO_Running' and 'Slave_SQL_Running' in the output. Both should be 'Yes'. If not, investigate the specific error messages provided by 'Last_IO_Error' or 'Last_SQL_Error'.

4

Ensure the slave is configured to connect to the master. Check 'Master_Host', 'Master_User', and 'Master_Port' in the 'SHOW SLAVE STATUS\G' output. If these are incorrect or missing, you'll need to reconfigure replication.

2. Check Network Connectivity Between Master and Slave medium

Confirm that the slave can reach the master on the specified replication port.

1

From the replication slave server, attempt to connect to the master's MySQL port (default is 3306) using telnet or netcat. Replace `master_ip_address` with the actual IP or hostname of your master.

telnet master_ip_address 3306

2

If the connection fails (e.g., 'Connection refused' or times out), there's a network issue. Check firewalls on both the master and slave servers, as well as any network devices in between, to ensure port 3306 is open and accessible from the slave to the master.

3

If you are using DNS names for the master, try pinging the master's hostname from the slave to verify DNS resolution is working correctly.

3. Review MySQL User Privileges for Replication medium

Verify that the replication user has the necessary permissions on the master server.

1

Connect to your MySQL master server as a user with sufficient privileges (e.g., root).

mysql -u root -p

2

Grant the necessary replication privileges to the user that the slave is using. Replace `replication_user`, `slave_ip_address`, and `replication_password` with your actual values.

GRANT REPLICATION SLAVE ON *.* TO 'replication_user'@'slave_ip_address' IDENTIFIED BY 'replication_password';
FLUSH PRIVILEGES;

3

If the slave is connecting from a hostname instead of an IP address, adjust the `'replication_user'@'slave_ip_address'` part accordingly.

4

Ensure the user exists and the password is correct by checking the `mysql.user` table or by attempting to connect from the slave using the replication credentials.

4. Restart Slave Threads and Re-establish Connection easy

A simple restart can often resolve transient connection issues.

1

Connect to your MySQL replication slave server.

mysql -u your_user -p

2

Stop the slave threads.

STOP SLAVE;

3

Reconfigure the slave to connect to the master. Replace `master_ip_address`, `replication_user`, `replication_password`, and `master_port` with your actual values.

CHANGE MASTER TO MASTER_HOST='master_ip_address', MASTER_USER='replication_user', MASTER_PASSWORD='replication_password', MASTER_PORT=master_port;
START SLAVE;

4

Check the slave status again to confirm that both threads are running and there are no new errors.

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Related Errors

5 related errors

MySQL Error 2023: Failed to Show Slave Hosts