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16.1.1.5 Creating a Data Snapshot Using mysqldump »
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16.1.1.4. Obtaining the Master Replication Information

To configure replication on the slave you must determine the master's current point within the master 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, then you must stop processing statements on the master, obtain the current position, and then dump the 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 get the master status information, follow these steps:

  1. Start 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.

    Warning

    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.

  2. Use the SHOW MASTER STATUS statement to determine the current binary log file name and offset on the master: 

    mysql > SHOW MASTER STATUS;
+---------------+----------+--------------+------------------+
| File          | Position | Binlog_Do_DB | Binlog_Ignore_DB |
+---------------+----------+--------------+------------------+
| mysql-bin.003 | 73       | test         | manual,mysql     |
+---------------+----------+--------------+------------------+

    The File column shows the name of the log file and Position shows the offset within the file. In this example, the binary log file is mysql-bin.003 and the offset 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 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”.

If you are setting up a brand new master and slave replication group, then you can exit the client and release the locks.