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MySQL Replication  /  ...  /  Setting Up Replication with Existing Data

2.2.5.4 Setting Up Replication with Existing Data

When setting up replication with existing data, transfer the snapshot from the source to the replica before starting replication. The process for importing data to the replica depends on how you created the snapshot of data on the source.

Choose one of the following:

If you used mysqldump:

  1. Start the replica, using the --skip-slave-start option so that replication does not start.

  2. Import the dump file:

    shell> mysql < fulldb.dump

If you created a snapshot using the raw data files:

  1. Extract the data files into the replica's data directory. For example:

    shell> tar xvf dbdump.tar

    You may need to set permissions and ownership on the files so that the replica server can access and modify them.

  2. Start the replica, using the --skip-slave-start option so that replication does not start.

  3. Configure the replica with the replication coordinates from the source. This tells the replica the binary log file and position within the file where replication needs to start. Also, configure the replica with the login credentials and host name of the source. For more information on the CHANGE MASTER TO statement required, see Section 2.2.5.2, “Setting the Source Configuration on the Replica”.

  4. Start the replication threads:

    mysql> START SLAVE;

After you have performed this procedure, the replica connects to the source and replicates any updates that have occurred on the source since the snapshot was taken.

If the server_id system variable for the source is not correctly set, replicas cannot connect to it. Similarly, if you have not set server_id correctly for the replica, you get the following error in the replica's error log:

Warning: You should set server-id to a non-0 value if master_host
is set; we will force server id to 2, but this MySQL server will
not act as a slave.

You also find error messages in the replica's error log if it is not able to replicate for any other reason.

The replica stores information about the source you have configured in its connection metadata repository. The connection metadata repository can be in the form of files or a table, as determined by the value set for the master_info_repository system variable. When a replica runs with master_info_repository=FILE, two files are stored in the data directory, named master.info and relay-log.info. If master_info_repository=TABLE instead, this information is saved in the master_slave_info table in the mysql database. In either case, do not remove or edit the files or table. Always use the CHANGE MASTER TO statement to change replication parameters. The replica can use the values specified in the statement to update the status files automatically. See Section 5.4, “Relay Log and Replication Metadata Repositories”, for more information.

Note

The contents of the connection metadata repository override some of the server options specified on the command line or in my.cnf. See Section 2.6, “Replication and Binary Logging Options and Variables”, for more details.

A single snapshot of the source suffices for multiple replicas. To set up additional replicas, use the same source snapshot and follow the replica portion of the procedure just described.