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13.4.2.1 CHANGE MASTER TO Syntax

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  1. CHANGE MASTER TO option [, option] ... [ channel_option ]
  2.  
  3. option:
  4.     MASTER_BIND = 'interface_name'
  5.   | MASTER_HOST = 'host_name'
  6.   | MASTER_USER = 'user_name'
  7.   | MASTER_PASSWORD = 'password'
  8.   | MASTER_PORT = port_num
  9.   | MASTER_CONNECT_RETRY = interval
  10.   | MASTER_RETRY_COUNT = count
  11.   | MASTER_DELAY = interval
  12.   | MASTER_HEARTBEAT_PERIOD = interval
  13.   | MASTER_LOG_FILE = 'master_log_name'
  14.   | MASTER_LOG_POS = master_log_pos
  15.   | MASTER_AUTO_POSITION = {0|1}
  16.   | RELAY_LOG_FILE = 'relay_log_name'
  17.   | RELAY_LOG_POS = relay_log_pos
  18.   | MASTER_SSL = {0|1}
  19.   | MASTER_SSL_CA = 'ca_file_name'
  20.   | MASTER_SSL_CAPATH = 'ca_directory_name'
  21.   | MASTER_SSL_CERT = 'cert_file_name'
  22.   | MASTER_SSL_CRL = 'crl_file_name'
  23.   | MASTER_SSL_CRLPATH = 'crl_directory_name'
  24.   | MASTER_SSL_KEY = 'key_file_name'
  25.   | MASTER_SSL_CIPHER = 'cipher_list'
  26.   | MASTER_SSL_VERIFY_SERVER_CERT = {0|1}
  27.   | MASTER_TLS_VERSION = 'protocol_list'
  28.   | MASTER_PUBLIC_KEY_PATH = 'key_file_name'
  29.   | GET_MASTER_PUBLIC_KEY = {0|1}
  30.   | IGNORE_SERVER_IDS = (server_id_list)
  31.  
  32. channel_option:
  33.     FOR CHANNEL channel
  34.  
  35. server_id_list:
  36.     [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:

  1. 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:

  • MASTER_HOST and MASTER_PORT are the host name (or IP address) of the master host and its TCP/IP port.

    Note

    Replication cannot use Unix socket files. You must be able to connect to the master MySQL server using TCP/IP.

    If you specify the MASTER_HOST or MASTER_PORT option, the slave assumes that the master server is different from before (even if the option value is the same as its current value.) In this case, the old values for the master binary log file name and position are considered no longer applicable, so if you do not specify MASTER_LOG_FILE and MASTER_LOG_POS in the statement, MASTER_LOG_FILE='' and MASTER_LOG_POS=4 are silently appended to it.

    Setting MASTER_HOST='' (that is, setting its value explicitly to an empty string) is not the same as not setting MASTER_HOST at all. Trying to set MASTER_HOST to an empty string fails with an error.

    Values used for MASTER_HOST and other CHANGE MASTER TO options are checked for linefeed (\n or 0x0A) characters; the presence of such characters in these values causes the statement to fail with ER_MASTER_INFO. (Bug #11758581, Bug #50801)

  • MASTER_USER and MASTER_PASSWORD are the user name and password of the account to use for connecting to the master.

    MASTER_USER cannot be made empty; setting MASTER_USER = '' or leaving it unset when setting a value for MASTER_PASSWORD causes an error (Bug #13427949).

    The password used for a MySQL Replication slave account in a CHANGE MASTER TO statement is limited to 32 characters in length; trying to use a password of more than 32 characters causes CHANGE MASTER TO to fail.

    The text of a running CHANGE MASTER TO statement, including values for MASTER_USER and MASTER_PASSWORD, can be seen in the output of a concurrent SHOW PROCESSLIST statement. (The complete text of a START SLAVE statement is also visible to SHOW PROCESSLIST.)

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 options perform the same functions as the --ssl-xxx options described in Section 6.4.2, “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 17.3.9, “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 17.3.9, “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 6.5.1.3, “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:

  • MASTER_PUBLIC_KEY_PATH indicates the path name to a file containing a slave-side copy of the public key required by the master for RSA key pair-based password exchange. The file must be in PEM format. This option applies to slaves that authenticate with the sha256_password or caching_sha2_password authentication plugin. (For sha256_password, MASTER_PUBLIC_KEY_PATH can be used only if MySQL was built using OpenSSL.)

  • GET_MASTER_PUBLIC_KEY indicates whether to request from the master the public key required for RSA key pair-based password exchange. This option applies to slaves that authenticate with the caching_sha2_password authentication plugin. For connections by accounts that authenticate using this plugin, the master does not send the public key unless requested, so it must be requested or specified in the client. If MASTER_PUBLIC_KEY_PATH is given and specifies a valid public key file, it takes precedence over GET_MASTER_PUBLIC_KEY.

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.

  • The slave_net_timeout system variable specifies the number of seconds that the slave waits for either more data or a heartbeat signal from the master, before the slave considers the connection broken, aborts the read, and tries to reconnect. The default value is 60 seconds (one minute).

  • The heartbeat interval, which stops the connection timeout occurring in the absence of data if the connection is still good, is controlled by the MASTER_HEARTBEAT_PERIOD option. A heartbeat signal is sent to the slave after that number of seconds, and the waiting period is reset whenever the master's binary log is updated with an event. Heartbeats are therefore sent by the master only if there are no unsent events in the binary log file for a period longer than this. The heartbeat interval interval is a decimal value having the range 0 to 4294967 seconds and a resolution in milliseconds; the smallest nonzero value is 0.001. Setting interval to 0 disables heartbeats altogether. The heartbeat interval defaults to half the value of the slave_net_timeout system variable. It is recorded in the master info log and shown in the replication_connection_configuration Performance Schema table. Issuing RESET SLAVE resets the heartbeat interval to the default value.

    Note that a change to the value or default setting of slave_net_timeout does not automatically change the heartbeat interval, whether that has been set explicitly or is using a previously calculated default. A warning is issued if you set @@GLOBAL.slave_net_timeout to a value less than that of the current heartbeat interval. If slave_net_timeout is changed, you must also issue CHANGE MASTER TO to adjust the heartbeat interval to an appropriate value so that the heartbeat signal occurs before the connection timeout. If you do not do this, the heartbeat signal has no effect, and if no data is received from the master, the slave can make repeated reconnection attempts, creating zombie dump threads.

  • If the slave does need to reconnect, the first retry occurs immediately after the timeout. MASTER_CONNECT_RETRY specifies the interval between reconnection attempts, and MASTER_RETRY_COUNT limits the number of reconnection attempts. If both the default settings are used, the slave waits 60 seconds between reconnection attempts (MASTER_CONNECT_RETRY=60), and keeps attempting to reconnect at this rate for 24 hours (MASTER_RETRY_COUNT=86400). These values are recorded in the master info log and shown in the replication_connection_configuration Performance Schema table. MASTER_RETRY_COUNT supersedes the --master-retry-count server startup option.

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 17.3.12, “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 13.7.6.34, “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:

  1. 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:

  • If the SQL thread is stopped, you can execute CHANGE MASTER TO using any combination that is otherwise allowed of RELAY_LOG_FILE, RELAY_LOG_POS, and MASTER_DELAY options, even if the slave I/O thread is running. No other options may be used with this statement when the I/O thread is running.

  • If the I/O thread is stopped, you can execute CHANGE MASTER TO using any of the options for this statement (in any allowed combination) except RELAY_LOG_FILE, RELAY_LOG_POS, or MASTER_DELAY, even when the SQL thread is running. These three options may not be used when the I/O thread is running.

  • Both the SQL thread and the I/O thread must be stopped before issuing a CHANGE MASTER TO statement that employs MASTER_AUTO_POSITION = 1.

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

For more information, see Section 17.3.8, “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:

  1. CHANGE MASTER TO
  2.   MASTER_HOST='master2.example.com',
  3.   MASTER_USER='replication',
  4.   MASTER_PASSWORD='password',
  5.   MASTER_PORT=3306,
  6.   MASTER_LOG_FILE='master2-bin.001',
  7.   MASTER_LOG_POS=4,
  8.   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):

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

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

Option Maximum Length
MASTER_HOST 60
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

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