17.1.1.5. Creating a Data Snapshot Using mysqldump

One way to create a snapshot of the data in an existing master database is to use the mysqldump tool. Once the data dump has been completed, you then import this data into the slave before starting the replication process.

To obtain a snapshot of the data using mysqldump:

  1. If you have not already locked the tables on the server to prevent statements that update data from executing:

    Start a session on the server 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;
    

    Remember to use SHOW MASTER STATUS and record the binary log details for use when starting up the slave. The point in time of your snapshot and the binary log position must match. See Section 17.1.1.4, “Obtaining the Replication Master Binary Log Coordinates”.

  2. In another session, use mysqldump to create a dump either of all the databases you want to replicate, or of selected individual databases. For example:

    shell> mysqldump --all-databases --lock-all-tables >dbdump.db
    

    An alternative to using a bare dump, is to use the --master-data option, which automatically appends the CHANGE MASTER TO statement required on the slave to start the replication process.

    shell> mysqldump --all-databases --master-data >dbdump.db
    
  3. In the client where you acquired the read lock, release the lock:

    mysql> UNLOCK TABLES;
    

    Alternatively, exit the first session to release the read lock.

When choosing databases to include in the dump, remember that you will need to filter out databases on each slave that you do not want to include in the replication process.

You will need either to copy the dump file to the slave, or to use the file from the master when connecting remotely to the slave to import the data.

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