17.1.1.4 Obtaining the Replication Source Binary Log Coordinates

To configure the replica to start the replication process at the correct point, you need to note the source's current coordinates within its binary log.

Warning

This procedure uses FLUSH TABLES WITH READ LOCK, which blocks COMMIT operations for InnoDB tables.

If you have existing data on your source server that you want to synchronize on your replicas before starting the replication process, you must stop processing statements on the source, and then obtain its current binary log coordinates and dump its data, before permitting the source to continue executing statements. If you do not stop the execution of statements, the data dump and the source status information that you use does not match and you may end up with inconsistent or corrupted databases on the replicas.

If you are planning to shut down the source to create a data snapshot, you can optionally skip this procedure and instead store a copy of the binary log index file along with the data snapshot. In that situation, the source creates a new binary log file on restart. The source's binary log coordinates where the replica must start the replication process are therefore the start of that new file, which is the next binary log file on the source following after the files that are listed in the copied binary log index file.

To obtain the source's binary log coordinates, follow these steps:

Start a session on the source 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;
```
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.
In a different session on the source, 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 replica. They represent the replication coordinates at which the replica should begin processing new updates from the source.
If the source has been running previously without binary logging enabled, the log file name and position values displayed by SHOW MASTER STATUS or mysqldump --master-data is empty. In that case, the values that you need to use later when specifying the binary log file and position are the empty string ('') and 4.

You now have the information you need to enable the replica 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 replica before you start replication, leave the client running so that the lock remains in place and then proceed to Section 17.1.1.5, “Creating a Data Snapshot Using mysqldump”, or Section 17.1.1.6, “Creating a Data Snapshot Using Raw Data Files”. The idea here is to prevent any further changes so that the data copied to the replicas is in synchrony with the source.

If you are setting up a brand new source and replica replication group, you can exit the first session to release the read lock.