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2.2.5.4 Setting Up Replication with Existing Data

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

Choose one of the following:

If you used mysqldump:

  1. Start the slave, 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 your slave data directory. For example:

    shell> tar xvf dbdump.tar

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

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

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

  4. Start the slave threads:

    mysql> START SLAVE;

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

If the server-id option for the master is not correctly set, slaves cannot connect to it. Similarly, if you have not set the server-id option correctly for the slave, you get the following error in the slave'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 slave's error log if it is not able to replicate for any other reason.

The slave stores information about the master you have configured in its master info repository. The master info repository can be in the form of files or a table, as determined by the value set for --master-info-repository. When a slave uses --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 slave can use the values specified in the statement to update the status files automatically. See Section 5.4, “Replication Relay and Status Logs”, for more information.

Note

The contents of the master info 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 master suffices for multiple slaves. To set up additional slaves, use the same master snapshot and follow the slave portion of the procedure just described.


User Comments
User comments in this section are, as the name implies, provided by MySQL users. The MySQL documentation team is not responsible for, nor do they endorse, any of the information provided here.
  Posted by Brian Kinney on September 10, 2015
I had a slave lose sync, and was trying to restore everything, with a minimum of effort.
When you want to resync an existing slave that failed and won't resync, I highly recommend using the mysqldump --master-data method.

1) It grabs all files.
2) It will put them back where they belong for you.
3) It collects the master status, and embeds it as SQL code for use upon restore.
4) It does not require you to stop the existing service, as it does the lock and unlock tables for you.

Reminder: you have to START SLAVE; once your MySQL < dump.db is applied.
Please then wait a good 90 seconds before expecting a valid answer to the question SHOW SLAVE STATUS;
You are looking for a YES on Slave_IO_Running and Slave_SQL_Running fields.
Even if you are not immediately in sync, you probably will be soon.

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