CHANGE MASTER TO doesn't actually change the master when using prepared statements. This is problematic for users who use orchestration frameworks that rely on prepared statements.
As an example, we can first set up a master:
MariaDB [(none)]> CHANGE MASTER TO master_host='orig_master', master_user='repl', master_password='password', master_log_file='localhost-bin.000002', master_log_pos=330;
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Query OK, 0 rows affected (0.05 sec)
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MariaDB [(none)]> SHOW SLAVE STATUS\G
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*************************** 1. row ***************************
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Slave_IO_State:
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Master_Host: orig_master
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Master_User: repl
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Master_Port: 3306
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Connect_Retry: 60
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Master_Log_File: localhost-bin.000002
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Read_Master_Log_Pos: 330
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Relay_Log_File: localhost-relay-bin.000001
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Relay_Log_Pos: 4
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Relay_Master_Log_File: localhost-bin.000002
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Slave_IO_Running: No
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Slave_SQL_Running: No
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Replicate_Do_DB:
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Replicate_Ignore_DB:
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Replicate_Do_Table:
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Replicate_Ignore_Table:
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Replicate_Wild_Do_Table:
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Replicate_Wild_Ignore_Table:
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Last_Errno: 0
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Last_Error:
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Skip_Counter: 0
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Exec_Master_Log_Pos: 330
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Relay_Log_Space: 248
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Until_Condition: None
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Until_Log_File:
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Until_Log_Pos: 0
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Master_SSL_Allowed: No
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Master_SSL_CA_File:
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Master_SSL_CA_Path:
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Master_SSL_Cert:
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Master_SSL_Cipher:
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Master_SSL_Key:
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Seconds_Behind_Master: NULL
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Master_SSL_Verify_Server_Cert: No
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Last_IO_Errno: 0
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Last_IO_Error:
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Last_SQL_Errno: 0
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Last_SQL_Error:
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Replicate_Ignore_Server_Ids:
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Master_Server_Id: 1
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Master_SSL_Crl:
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Master_SSL_Crlpath:
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Using_Gtid: No
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Gtid_IO_Pos:
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1 row in set (0.00 sec)
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Then let's try to change it via a prepared statement:
MariaDB [(none)]> SET @s := "CHANGE MASTER TO master_host='new_master', master_user='repl', master_password='password', master_log_file='localhost-bin.000002', master_log_pos=330";
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Query OK, 0 rows affected (0.00 sec)
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MariaDB [(none)]> PREPARE st FROM @s;
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Query OK, 0 rows affected (0.00 sec)
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Statement prepared
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MariaDB [(none)]> EXECUTE st;
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Query OK, 0 rows affected (0.04 sec)
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MariaDB [(none)]> DEALLOCATE PREPARE st;
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Query OK, 0 rows affected (0.00 sec)
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We don't get any errors, so it sounds like things are OK, but the master hasn't actually been changed:
MariaDB [(none)]> SHOW SLAVE STATUS\G
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*************************** 1. row ***************************
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Slave_IO_State:
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Master_Host: orig_master
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Master_User: repl
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Master_Port: 3306
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Connect_Retry: 60
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Master_Log_File: localhost-bin.000002
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Read_Master_Log_Pos: 330
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Relay_Log_File: localhost-relay-bin.000001
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Relay_Log_Pos: 4
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Relay_Master_Log_File: localhost-bin.000002
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Slave_IO_Running: No
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Slave_SQL_Running: No
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Replicate_Do_DB:
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Replicate_Ignore_DB:
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Replicate_Do_Table:
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Replicate_Ignore_Table:
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Replicate_Wild_Do_Table:
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Replicate_Wild_Ignore_Table:
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Last_Errno: 0
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Last_Error:
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Skip_Counter: 0
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Exec_Master_Log_Pos: 330
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Relay_Log_Space: 248
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Until_Condition: None
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Until_Log_File:
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Until_Log_Pos: 0
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Master_SSL_Allowed: No
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Master_SSL_CA_File:
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Master_SSL_CA_Path:
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Master_SSL_Cert:
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Master_SSL_Cipher:
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Master_SSL_Key:
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Seconds_Behind_Master: NULL
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Master_SSL_Verify_Server_Cert: No
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Last_IO_Errno: 0
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Last_IO_Error:
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Last_SQL_Errno: 0
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Last_SQL_Error:
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Replicate_Ignore_Server_Ids:
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Master_Server_Id: 1
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Master_SSL_Crl:
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Master_SSL_Crlpath:
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Using_Gtid: No
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Gtid_IO_Pos:
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1 row in set (0.00 sec)
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The wrong change goes into the error log as well:
150226 9:21:48 [Note] 'CHANGE MASTER TO executed'. Previous state master_host='orig_master', master_port='3306', master_log_file='localhost-bin.000002', master_log_pos='330'. New state master_host='orig_master', master_port='3306', master_log_file='localhost-bin.000002', master_log_pos='330'.
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Bug
Major
