To configure replication on the slave you must determine the master's current coordinates within its binary log. You will need this information so that when the slave starts the replication process, it is able to start processing events from the binary log at the correct point.
If you have existing data on your master that you want to synchronize on your slaves before starting the replication process, you must stop processing statements on the master, and then obtain its current binary log coordinates and dump its data, before allowing the master to continue executing statements. If you do not stop the execution of statements, the data dump and the master status information that you use will not match and you will end up with inconsistent or corrupted databases on the slaves.
To obtain the master binary log coordinates, follow these steps:
Start a session on the master by connecting to it with the
command-line client, and flush all tables and block write
statements by executing the
FLUSH TABLES WITH
READ LOCK
statement:
mysql> FLUSH TABLES WITH READ LOCK;
For InnoDB
tables, note that
FLUSH TABLES WITH
READ LOCK
also blocks
COMMIT
operations.
Leave the client from which you issued the
FLUSH
TABLES
statement running so that the read lock
remains in effect. If you exit the client, the lock is
released.
In a different session on the master, use the
SHOW MASTER STATUS
statement
to determine the current binary log file name and position:
mysql > SHOW MASTER STATUS;
+------------------+----------+--------------+------------------+
| File | Position | Binlog_Do_DB | Binlog_Ignore_DB |
+------------------+----------+--------------+------------------+
| mysql-bin.000003 | 73 | test | manual,mysql |
+------------------+----------+--------------+------------------+
The File
column shows the name of the log
file and Position
shows the position
within the file. In this example, the binary log file is
mysql-bin.000003
and the position is 73.
Record these values. You need them later when you are
setting up the slave. They represent the replication
coordinates at which the slave should begin processing new
updates from the master.
If the master has been running previously without binary
logging enabled, the log file name and position values
displayed by SHOW MASTER
STATUS
or mysqldump
--master-data will be empty. In that case, the
values that you need to use later when specifying the
slave's log file and position are the empty string
(''
) and 4
.
You now have the information you need to enable the slave to start reading from the binary log in the correct place to start replication.
If you have existing data that needs be to synchronized with the slave before you start replication, leave the client running so that the lock remains in place and then proceed to Section 16.1.1.5, “Creating a Data Snapshot Using mysqldump”, or Section 16.1.1.6, “Creating a Data Snapshot Using Raw Data Files”. The idea here is to prevent any further changes so that the data copied to the slaves is in synchrony with the master.
If you are setting up a brand new master and slave replication group, you can exit the first session to release the read lock.
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