How to create a new (or repair a broken) GTID based slave

MySQL 5.6 introduced the new Global Transaction ID (GTID) support in replication. Percona XtraBackup automatically stores the GTID value in the xtrabackup_binlog_info when doing the backup of MySQL and Percona Server for MySQL 5.7 with the GTID mode enabled. This information can be used to create a new (or repair a broken) GTID based replica.

STEP 1: Take a backup from any server on the replication environment, source or replica.

The following command takes a backup and saves it in the /data/backups/$TIMESTAMP folder:

$ innobackupex /data/backups/

In the destination folder, there will be a file with the name xtrabackup_binlog_info. This file contains both binary log coordinates and the GTID information.

$ cat xtrabackup_binlog_info
mysql-bin.000002    1232        c777888a-b6df-11e2-a604-080027635ef5:1-4

That information is also printed by innobackupex after taking the backup:

innobackupex: MySQL binlog position: filename 'mysql-bin.000002', position 1232, GTID of the last change 'c777888a-b6df-11e2-a604-080027635ef5:1-4'

STEP 2: Prepare the backup

The backup will be prepared with the following command:

TheMaster$ innobackupex --apply-log /data/backups/$TIMESTAMP/

You need to select the path where your snapshot has been taken, for example /data/backups/2013-05-07_08-33-33. If everything is ok you should get the same OK message. Now, the transaction logs are applied to the data files, and new ones are created: your data files are ready to be used by the MySQL server.

STEP 3: Move the backup to the destination server

Use rsync or scp to copy the data to the destination server. If you are synchronizing the data directly to the already running replica’s data directory it is advised to stop the MySQL server there.

$ rsync -avprP -e ssh /path/to/backupdir/$TIMESTAMP NewSlave:/path/to/mysql/

After you copy the data over, make sure MySQL has proper permissions to access them.

$ chown mysql:mysql /path/to/mysql/datadir

STEP 4: Configure and start replication

Set the gtid_purged variable to the GTID from xtrabackup_binlog_info. Then, update the information about the source node and, finally, start the replica.

# Using the mysql shell
NewSlave > SET SESSION wsrep_on = 0;
NewSlave > RESET MASTER;
NewSlave > SET SESSION wsrep_on = 1;
NewSlave > SET GLOBAL gtid_purged='<gtid_string_found_in_xtrabackup_binlog_info>';
NewSlave > CHANGE MASTER TO
             MASTER_HOST="$masterip",
             MASTER_USER="repl",
             MASTER_PASSWORD="$slavepass",
             MASTER_AUTO_POSITION = 1;
NewSlave > START SLAVE;

Note

The example above is applicable to Percona XtraDB Cluster. The wsrep_on variable is set to 0 before resetting the source (RESET MASTER). The reason is that Percona XtraDB Cluster will not allow resetting the source if wsrep_on=1.

STEP 5: Check the replication status

Following command will show the replica status:

NewSlave > SHOW SLAVE STATUS\G
         [..]
         Slave_IO_Running: Yes
         Slave_SQL_Running: Yes
         [...]
         Retrieved_Gtid_Set: c777888a-b6df-11e2-a604-080027635ef5:5
         Executed_Gtid_Set: c777888a-b6df-11e2-a604-080027635ef5:1-5

We can see that the replica has retrieved a new transaction with number 5, so transactions from 1 to 5 are already on this replica.

That’s all, we have created a new replica in our GTID based replication environment.

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