How to Check Replication Status in MySQL Quickly

To check replication status in MySQL, use the SHOW SLAVE STATUS\G command on the replica server. This command shows detailed information about the replication process, including whether it is running correctly and any errors.

Syntax

The main command to check replication status on a MySQL replica is SHOW SLAVE STATUS\G. It returns a detailed report about the replication threads and their current state.

• SHOW SLAVE STATUS\G: Displays replication status in a vertical format for readability.
• Slave_IO_Running: Shows if the IO thread is running (Yes/No).
• Slave_SQL_Running: Shows if the SQL thread is running (Yes/No).
• Last_Error: Displays the last error message if replication failed.

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SHOW SLAVE STATUS\G

Example

This example shows how to run the command on a replica server and interpret key fields to confirm replication is working.

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mysql> SHOW SLAVE STATUS\G
*************************** 1. row ***************************
               Slave_IO_State: Waiting for master to send event
                  Master_Host: 192.168.1.100
                  Master_User: repl_user
                  Slave_IO_Running: Yes
                 Slave_SQL_Running: Yes
                   Last_Error:
             Seconds_Behind_Master: 0

Output

Slave_IO_Running: Yes
Slave_SQL_Running: Yes
Last_Error: (empty)
Seconds_Behind_Master: 0

Common Pitfalls

Common mistakes when checking replication status include:

• Running SHOW SLAVE STATUS on the master server instead of the replica.
• Ignoring the Slave_IO_Running or Slave_SQL_Running fields which indicate if replication threads are active.
• Not checking Last_Error for replication problems.
• Confusing Seconds_Behind_Master which shows replication lag but can be NULL if replication is broken.

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/* Wrong: Running on master server */
mysql> SHOW SLAVE STATUS\G
/* Output is empty because master has no slave status */

/* Right: Run on replica server */
mysql> SHOW SLAVE STATUS\G
Slave_IO_Running: Yes
Slave_SQL_Running: Yes
Last_Error: (empty)

Quick Reference

Field	Meaning
Slave_IO_Running	Shows if the IO thread is running (Yes/No)
Slave_SQL_Running	Shows if the SQL thread is running (Yes/No)
Last_Error	Last replication error message, empty if none
Seconds_Behind_Master	Replication lag in seconds, 0 means up to date
Master_Host	IP or hostname of the master server

Key Takeaways

Use SHOW SLAVE STATUS\G on the replica to check replication status.

Check Slave_IO_Running and Slave_SQL_Running fields to confirm replication threads are active.

Look at Last_Error to detect any replication problems.

Seconds_Behind_Master shows how delayed the replica is compared to the master.

Do not run SHOW SLAVE STATUS on the master server; it returns no data there.