What is the 'Binary Log Coordinates' aka '--master-data' flag in DB?

Binary log coordinates are a set of values that identify a specific location in the binary log of a database server. These values include the name of the binary log file and the position within that file. Binary log coordinates are used to keep track of the changes made to a database server, and are especially useful for incremental backups and point-in-time recovery.

During a backup, binary log coordinates can be included in the backup file using the --master-data option in MySQL. When this option is set to 1, the binary log file name and position are included in the backup file as a comment. When set to 2, the binary log coordinates are written to the backup file as SQL statements that are executed during the restore process.

Here's an example of how to include binary log coordinates in a MySQL backup:

mysqldump -u username -p --databases database_name --master-data=2 > backup.sql

In this example, the --master-data=2 option is used to write the binary log coordinates to the backup file as SQL statements.

During a restore, binary log coordinates are used to identify the point in time to which the database should be restored. The mysqlbinlog utility can be used to read the binary log and extract the relevant SQL statements for a point-in-time recovery. Here's an example of how to use binary log coordinates for a point-in-time recovery in MySQL:

1. Determine the binary log coordinates for the desired restore point using the SHOW MASTER STATUS; command in MySQL.

2. Restore the full backup file.

3. Use mysqlbinlog to extract the relevant SQL statements from the binary log file:

    mysqlbinlog --start-position=<position> <binary_log_file> | mysql -u username -p
   

   In this command, <position> is the position within the binary log file and <binary_log_file> is the name of the binary log file. The extracted SQL statements are piped to the mysql utility to apply them to the restored database.

By including binary log coordinates in a database backup, you can ensure that you have a complete record of all changes made to the database server, and that you can restore the database to a specific point in time if necessary.