MySQL 8.0 Reference Manual Including MySQL NDB Cluster 8.0

13.4.2.1 CHANGE MASTER TO Syntax

CHANGE MASTER TO option [, option] ... [ channel_option ]

option:
    MASTER_BIND = 'interface_name'
  | MASTER_HOST = 'host_name'
  | MASTER_USER = 'user_name'
  | MASTER_PASSWORD = 'password'
  | MASTER_PORT = port_num
  | PRIVILEGE_CHECKS_USER = {'account' | NULL}
  | MASTER_CONNECT_RETRY = interval
  | MASTER_RETRY_COUNT = count
  | MASTER_DELAY = interval
  | MASTER_HEARTBEAT_PERIOD = interval
  | MASTER_LOG_FILE = 'master_log_name'
  | MASTER_LOG_POS = master_log_pos
  | MASTER_AUTO_POSITION = {0|1}
  | RELAY_LOG_FILE = 'relay_log_name'
  | RELAY_LOG_POS = relay_log_pos
  | MASTER_COMPRESSION_ALGORITHMS = 'value'
  | MASTER_ZSTD_COMPRESSION_LEVEL = level
  | MASTER_SSL = {0|1}
  | MASTER_SSL_CA = 'ca_file_name'
  | MASTER_SSL_CAPATH = 'ca_directory_name'
  | MASTER_SSL_CERT = 'cert_file_name'
  | MASTER_SSL_CRL = 'crl_file_name'
  | MASTER_SSL_CRLPATH = 'crl_directory_name'
  | MASTER_SSL_KEY = 'key_file_name'
  | MASTER_SSL_CIPHER = 'cipher_list'
  | MASTER_SSL_VERIFY_SERVER_CERT = {0|1}
  | MASTER_TLS_VERSION = 'protocol_list'
  | MASTER_PUBLIC_KEY_PATH = 'key_file_name'
  | GET_MASTER_PUBLIC_KEY = {0|1}
  | IGNORE_SERVER_IDS = (server_id_list)

channel_option:
    FOR CHANNEL channel

server_id_list:
    [server_id [, server_id] ... ]

CHANGE MASTER TO changes the parameters that the slave server uses for connecting to the master server, for reading the master binary log, and reading the slave relay log. It also updates the contents of the master info and relay log info repositories (see Section 17.2.4, “Replication Relay and Status Logs”). CHANGE MASTER TO requires the REPLICATION_SLAVE_ADMIN or SUPER privilege.

You can issue CHANGE MASTER TO statements on a running slave without first stopping it, depending on the states of the slave SQL thread and slave I/O thread. The rules governing such use are provided later in this section.

When using a multithreaded slave (in other words slave_parallel_workers is greater than 0), stopping the slave can cause gaps in the sequence of transactions that have been executed from the relay log, regardless of whether the slave was stopped intentionally or otherwise. When such gaps exist, issuing CHANGE MASTER TO fails. The solution in this situation is to issue START SLAVE UNTIL SQL_AFTER_MTS_GAPS which ensures that the gaps are closed.

The optional FOR CHANNEL channel clause enables you to name which replication channel the statement applies to. Providing a FOR CHANNEL channel clause applies the CHANGE MASTER TO statement to a specific replication channel, and is used to add a new channel or modify an existing channel. For example, to add a new channel called channel2:

CHANGE MASTER TO MASTER_HOST=host1, MASTER_PORT=3002 FOR CHANNEL 'channel2'

If no clause is named and no extra channels exist, the statement applies to the default channel.

When using multiple replication channels, if a CHANGE MASTER TO statement does not name a channel using a FOR CHANNEL channel clause, an error occurs. See Section 17.2.3, “Replication Channels” for more information.

Options not specified retain their value, except as indicated in the following discussion. Thus, in most cases, there is no need to specify options that do not change.

MASTER_HOST, MASTER_USER, MASTER_PASSWORD, and MASTER_PORT provide information to the slave about how to connect to its master:

PRIVILEGE_CHECKS_USER (available as of MySQL 8.0.18) names a user account that supplies a security context for the specified channel. NULL, which is the default, means no security context is used. If you do not specify a channel and no other channels exist, the statement is applied to the default channel. For example, to start privilege checks on the channel channel_1 on a running replication slave, issue the following statements:

mysql> STOP SLAVE FOR CHANNEL 'channel_1';
mysql> CHANGE MASTER TO PRIVILEGE_CHECKS_USER = 'priv_repl'@'%.example.com' FOR CHANNEL 'channel_1'; 
mysql> START SLAVE FOR CHANNEL 'channel_1';

The user name and host name for the user account must follow the syntax described in Section 6.2.4, “Specifying Account Names”, and the user must not be an anonymous user (with a blank user name) or the CURRENT_USER. The account must have the REPLICATION_APPLIER privilege, plus the required privileges to execute the transactions replicated on the channel. When you restart the replication channel, the privilege checks are applied from that point on. For more information, see Section 17.3.3, “Replication Privilege Checks”.

MASTER_COMPRESSION_ALGORITHMS and MASTER_ZSTD_COMPRESSION_LEVEL (available as of MySQL 8.0.18) enable control over the use of compression for connections to the master:

For more information, see Section 4.2.6, “Connection Compression Control”.

The MASTER_SSL_xxx options and the MASTER_TLS_VERSION option specify how the slave uses encryption and ciphers to secure the replication connection. These options can be changed even on slaves that are compiled without SSL support. They are saved to the master info repository, but are ignored if the slave does not have SSL support enabled. The MASTER_SSL_xxx and MASTER_TLS_VERSION options perform the same functions as the --ssl-xxx and --tls-version client options described in Command Options for Encrypted Connections. The correspondence between the two sets of options, and the use of the MASTER_SSL_xxx and MASTER_TLS_VERSION options to set up a secure connection, is explained in Section 17.3.1, “Setting Up Replication to Use Encrypted Connections”.

Important

To connect to the replication master using a user account that authenticates with the caching_sha2_password plugin, you must either set up a secure connection as described in Section 17.3.1, “Setting Up Replication to Use Encrypted Connections”, or enable the unencrypted connection to support password exchange using an RSA key pair. The caching_sha2_password authentication plugin is the default for new users created from MySQL 8.0 (for details, see Section 6.4.1.2, “Caching SHA-2 Pluggable Authentication”). If the user account that you create or use for replication (as specified by the MASTER_USER option) uses this authentication plugin, and you are not using a secure connection, you must enable RSA key pair-based password exchange for a successful connection.

To enable RSA key pair-based password exchange, specify either the MASTER_PUBLIC_KEY_PATH or the GET_MASTER_PUBLIC_KEY=1 option. Either of these options provides the RSA public key to the slave:

The MASTER_HEARTBEAT_PERIOD, MASTER_CONNECT_RETRY, and MASTER_RETRY_COUNT options control how the slave recognizes that the connection to the master has been lost and makes attempts to reconnect.

MASTER_DELAY specifies how many seconds behind the master the slave must lag. An event received from the master is not executed until at least interval seconds later than its execution on the master. The default is 0. An error occurs if interval is not a nonnegative integer in the range from 0 to 231−1. For more information, see Section 17.4.10, “Delayed Replication”.

A CHANGE MASTER TO statement employing the MASTER_DELAY option can be executed on a running slave when the slave SQL thread is stopped.

MASTER_BIND is for use on replication slaves having multiple network interfaces, and determines which of the slave's network interfaces is chosen for connecting to the master.

The address configured with this option, if any, can be seen in the Master_Bind column of the output from SHOW SLAVE STATUS. In the master info repository table mysql.slave_master_info, the value can be seen as the Master_bind column.

The ability to bind a replication slave to a specific network interface is also supported by NDB Cluster.

MASTER_LOG_FILE and MASTER_LOG_POS are the coordinates at which the slave I/O thread should begin reading from the master the next time the thread starts. RELAY_LOG_FILE and RELAY_LOG_POS are the coordinates at which the slave SQL thread should begin reading from the relay log the next time the thread starts. If you specify either of MASTER_LOG_FILE or MASTER_LOG_POS, you cannot specify RELAY_LOG_FILE or RELAY_LOG_POS. If you specify either of MASTER_LOG_FILE or MASTER_LOG_POS, you also cannot specify MASTER_AUTO_POSITION = 1 (described later in this section). If neither of MASTER_LOG_FILE or MASTER_LOG_POS is specified, the slave uses the last coordinates of the slave SQL thread before CHANGE MASTER TO was issued. This ensures that there is no discontinuity in replication, even if the slave SQL thread was late compared to the slave I/O thread, when you merely want to change, say, the password to use.

A CHANGE MASTER TO statement employing RELAY_LOG_FILE, RELAY_LOG_POS, or both options can be executed on a running slave when the slave SQL thread is stopped. Relay logs are preserved if at least one of the slave SQL thread and the slave I/O thread is running; if both threads are stopped, all relay log files are deleted unless at least one of RELAY_LOG_FILE or RELAY_LOG_POS is specified.

RELAY_LOG_FILE can use either an absolute or relative path, and uses the same base name as MASTER_LOG_FILE.

When MASTER_AUTO_POSITION = 1 is used with CHANGE MASTER TO, the slave attempts to connect to the master using the GTID-based replication protocol. This option can be used with CHANGE MASTER TO only if both the slave SQL and slave I/O threads are stopped. Both the slave and the master must have GTIDs enabled (GTID_MODE=ON, ON_PERMISSIVE, or OFF_PERMISSIVE on the slave, and GTID_MODE=ON on the master). Auto-positioning is used for the connection, so the coordinates represented by MASTER_LOG_FILE and MASTER_LOG_POS are not used, and the use of either or both of these options together with MASTER_AUTO_POSITION = 1 causes an error. If multi-source replication is enabled on the slave, you need to set the MASTER_AUTO_POSITION = 1 option for each applicable replication channel.

With MASTER_AUTO_POSITION = 1 set, in the initial connection handshake, the slave sends a GTID set containing the transactions that it has already received, committed, or both. The master responds by sending all transactions recorded in its binary log whose GTID is not included in the GTID set sent by the slave. This exchange ensures that the master only sends the transactions with a GTID that the slave has not already recorded or committed. If the slave receives transactions from more than one master, as in the case of a diamond topology, the auto-skip function ensures that the transactions are not applied twice. For details of how the GTID set sent by the slave is computed, see Section 17.1.3.3, “GTID Auto-Positioning”.

If any of the transactions that should be sent by the master have been purged from the master's binary log, or added to the set of GTIDs in the gtid_purged system variable by another method, the master sends the error ER_MASTER_HAS_PURGED_REQUIRED_GTIDS to the slave, and replication does not start. The GTIDs of the missing purged transactions are identified and listed in the master's error log in the warning message ER_FOUND_MISSING_GTIDS. Also, if during the exchange of transactions it is found that the slave has recorded or committed transactions with the master's UUID in the GTID, but the master itself has not committed them, the master sends the error ER_SLAVE_HAS_MORE_GTIDS_THAN_MASTER to the slave and replication does not start. For information on how to handle these situations, see Section 17.1.3.3, “GTID Auto-Positioning”.

You can see whether replication is running with auto-positioning enabled by checking the Performance Schema replication_connection_status table or the output of SHOW SLAVE STATUS. Disabling the MASTER_AUTO_POSITION option again makes the slave revert to file-based replication, in which case you must also specify one or both of the MASTER_LOG_FILE or MASTER_LOG_POS options.

IGNORE_SERVER_IDS takes a comma-separated list of 0 or more server IDs. Events originating from the corresponding servers are ignored, with the exception of log rotation and deletion events, which are still recorded in the relay log.

In circular replication, the originating server normally acts as the terminator of its own events, so that they are not applied more than once. Thus, this option is useful in circular replication when one of the servers in the circle is removed. Suppose that you have a circular replication setup with 4 servers, having server IDs 1, 2, 3, and 4, and server 3 fails. When bridging the gap by starting replication from server 2 to server 4, you can include IGNORE_SERVER_IDS = (3) in the CHANGE MASTER TO statement that you issue on server 4 to tell it to use server 2 as its master instead of server 3. Doing so causes it to ignore and not to propagate any statements that originated with the server that is no longer in use.

If IGNORE_SERVER_IDS contains the server's own ID and the server was started with the --replicate-same-server-id option enabled, an error results.

Note

When global transaction identifiers (GTIDs) are used for replication, transactions that have already been applied are automatically ignored, so the IGNORE_SERVER_IDS function is not required and is deprecated. If gtid_mode=ON is set for the server, a deprecation warning is issued if you include the IGNORE_SERVER_IDS option in a CHANGE MASTER TO statement.

The master info repository and the output of SHOW SLAVE STATUS provide the list of servers that are currently ignored. For more information, see Section 17.2.4.2, “Slave Status Logs”, and Section 13.7.7.34, “SHOW SLAVE STATUS Syntax”.

If a CHANGE MASTER TO statement is issued without any IGNORE_SERVER_IDS option, any existing list is preserved. To clear the list of ignored servers, it is necessary to use the option with an empty list:

CHANGE MASTER TO IGNORE_SERVER_IDS = ();

RESET SLAVE ALL clears IGNORE_SERVER_IDS.

Note

A deprecation warning is issued if SET GTID_MODE=ON is issued when any channel has existing server IDs set with IGNORE_SERVER_IDS. Before starting GTID-based replication, check for and clear all ignored server ID lists on the servers involved. The SHOW_SLAVE_STATUS statement displays the list of ignored IDs, if there is one. If you do receive the deprecation warning, you can still clear a list after gtid_mode=ON is set by issuing a CHANGE MASTER TO statement containing the IGNORE_SERVER_IDS option with an empty list.

Invoking CHANGE MASTER TO causes the previous values for MASTER_HOST, MASTER_PORT, MASTER_LOG_FILE, and MASTER_LOG_POS to be written to the error log, along with other information about the slave's state prior to execution.

CHANGE MASTER TO causes an implicit commit of an ongoing transaction. See Section 13.3.3, “Statements That Cause an Implicit Commit”.

From MySQL 5.7, the strict requirement to execute STOP SLAVE prior to issuing any CHANGE MASTER TO statement (and START SLAVE afterward) is removed. Instead of depending on whether the slave is stopped, the behavior of CHANGE MASTER TO depends on the states of the slave SQL thread and slave I/O threads; which of these threads is stopped or running now determines the options that can or cannot be used with a CHANGE MASTER TO statement at a given point in time. The rules for making this determination are listed here:

You can check the current state of the slave SQL and I/O threads using SHOW SLAVE STATUS.

For more information, see Section 17.4.8, “Switching Masters During Failover”.

If you are using statement-based replication and temporary tables, it is possible for a CHANGE MASTER TO statement following a STOP SLAVE statement to leave behind temporary tables on the slave. A warning (ER_WARN_OPEN_TEMP_TABLES_MUST_BE_ZERO) is now issued whenever this occurs. You can avoid this in such cases by making sure that the value of the Slave_open_temp_tables system status variable is equal to 0 prior to executing such a CHANGE MASTER TO statement.

CHANGE MASTER TO is useful for setting up a slave when you have the snapshot of the master and have recorded the master binary log coordinates corresponding to the time of the snapshot. After loading the snapshot into the slave to synchronize it with the master, you can run CHANGE MASTER TO MASTER_LOG_FILE='log_name', MASTER_LOG_POS=log_pos on the slave to specify the coordinates at which the slave should begin reading the master binary log.

The following example changes the master server the slave uses and establishes the master binary log coordinates from which the slave begins reading. This is used when you want to set up the slave to replicate the master:

CHANGE MASTER TO
  MASTER_HOST='master2.example.com',
  MASTER_USER='replication',
  MASTER_PASSWORD='password',
  MASTER_PORT=3306,
  MASTER_LOG_FILE='master2-bin.001',
  MASTER_LOG_POS=4,
  MASTER_CONNECT_RETRY=10;

The next example shows an operation that is less frequently employed. It is used when the slave has relay log files that you want it to execute again for some reason. To do this, the master need not be reachable. You need only use CHANGE MASTER TO and start the SQL thread (START SLAVE SQL_THREAD):

CHANGE MASTER TO
  RELAY_LOG_FILE='slave-relay-bin.006',
  RELAY_LOG_POS=4025;

The following table shows the maximum permissible length for the string-valued options.

Option Maximum Length
MASTER_HOST 255 (60 prior to MySQL 8.0.17)
MASTER_USER 96
MASTER_PASSWORD 32
MASTER_LOG_FILE 511
RELAY_LOG_FILE 511
MASTER_SSL_CA 511
MASTER_SSL_CAPATH 511
MASTER_SSL_CERT 511
MASTER_SSL_CRL 511
MASTER_SSL_CRLPATH 511
MASTER_SSL_KEY 511
MASTER_SSL_CIPHER 511
MASTER_TLS_VERSION 511
MASTER_PUBLIC_KEY_PATH 511
MASTER_COMPRESSION_ALGORITHMS 99