When setting up replication with existing data, you will need to decide how best to get the data from the master to the slave before starting the replication service.
The basic process for setting up replication with existing data is as follows:
With the MySQL master running, create a user to be used by the slave when connecting to the master during replication. See Section 17.1.1.3, “Creating a User for Replication”.
If you have not already configured the
server-idand enabled binary logging on the master server, you will need to shut it down to configure these options. See Section 17.1.1.1, “Setting the Replication Master Configuration”.If you have to shut down your master server, this is a good opportunity to take a snapshot of its databases. You should obtain the master status (see Section 17.1.1.4, “Obtaining the Replication Master Binary Log Coordinates”) before taking down the master, updating the configuration and taking a snapshot. For information on how to create a snapshot using raw data files, see Section 17.1.1.6, “Creating a Data Snapshot Using Raw Data Files”.
If your master server is already correctly configured, obtain its status (see Section 17.1.1.4, “Obtaining the Replication Master Binary Log Coordinates”) and then use mysqldump to take a snapshot (see Section 17.1.1.5, “Creating a Data Snapshot Using mysqldump”) or take a raw snapshot of the live server using the guide in Section 17.1.1.6, “Creating a Data Snapshot Using Raw Data Files”.
Update the configuration of the slave. See Section 17.1.1.2, “Setting the Replication Slave Configuration”.
The next step depends on how you created the snapshot of data on the master.
If you used mysqldump:
Start the slave, using the
--skip-slave-startoption so that replication does not start.Import the dump file:
shell>
mysql < fulldb.dump
If you created a snapshot using the raw data files:
Extract the data files into your slave data directory. For example:
shell>
tar xvf dbdump.tarYou may need to set permissions and ownership on the files so that the slave server can access and modify them.
Start the slave, using the
--skip-slave-startoption so that replication does not start.
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 TOstatement required, see Section 17.1.1.10, “Setting the Master Configuration on the Slave”.Start the slave threads:
mysql>
START SLAVE;
After you have performed this procedure, the slave should connect to the master and catch up on any updates that have occurred since the snapshot was taken.
If you have forgotten to set the
server-id option for the master,
slaves cannot connect to it.
If you have forgotten to set the
server-id option 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.
Once a slave is replicating, you can find in its data directory
one file named master.info and another
named relay-log.info. The slave uses these
two files to keep track of how much of the master's binary log
it has processed. Do not remove or edit
these files unless you know exactly what you are doing and fully
understand the implications. Even in that case, it is preferred
that you use the CHANGE MASTER TO
statement to change replication parameters. The slave will use
the values specified in the statement to update the status files
automatically.
The content of master.info overrides some
of the server options specified on the command line or in
my.cnf. See
Section 17.1.3, “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.