How to create a new (or repair a broken) GTID-based replica¶
MySQL 5.6 introduced the 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.
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:
$ xtrabackup --backup --target-dirs=/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
Expected output
mysql-bin.000002 1232 c777888a-b6df-11e2-a604-080027635ef5:1-4
That information is also printed by xtrabackup after taking the backup:
Expected output
xtrabackup: MySQL binlog position: filename 'mysql-bin.000002', position 1232, GTID of the last change 'c777888a-b6df-11e2-a604-080027635ef5:1-4'
2. Prepare the backup¶
The backup will be prepared with the following command on the Source:
$ xtrabackup --prepare --target-dir=/data/backup
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.
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
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. Run the following commands on
the replica if you are using a version before 8.0.22:
# Using the mysql shell
> SET SESSION wsrep_on = 0;
> RESET MASTER;
> SET SESSION wsrep_on = 1;
> SET GLOBAL gtid_purged='<gtid_string_found_in_xtrabackup_binlog_info>';
> CHANGE MASTER TO
MASTER_HOST="$masterip",
MASTER_USER="repl",
MASTER_PASSWORD="$slavepass",
MASTER_AUTO_POSITION = 1;
> START SLAVE;
If you are using version 8.0.22 or later, use START REPLICA instead
of START SLAVE. START SLAVE is deprecated as of that release. If you
are using version 8.0.21 or earlier, use START SLAVE.
If you are using a version 8.0.23 or later, run the following commands:
# Using the mysql shell
> SET SESSION wsrep_on = 0;
> RESET MASTER;
> SET SESSION wsrep_on = 1;
> SET GLOBAL gtid_purged='<gtid_string_found_in_xtrabackup_binlog_info>';
> CHANGE REPLICATION SOURCE TO
SOURCE_HOST="$masterip",
SOURCE_USER="repl",
SOURCE_PASSWORD="$slavepass",
SOURCE_AUTO_POSITION = 1;
> START REPLICA;
If you are using version 8.0.23 or later,
use CHANGE_REPLICATION_SOURCE_TO and the appropriate options. CHANGE_MASTER_TO is deprecated as of that release.
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.
5. Check the replication status¶
The following command returns the replica status:
mysql> SHOW REPLICA STATUS\G
Expected output
[..]
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
Note
The command SHOW SLAVE STATUS is deprecated. Use SHOW REPLICA STATUS.
We can see that the replica has retrieved a new transaction with number 5, so transactions from 1 to 5 are already on this slave.
We have created a new replica in our GTID based replication
environment.
Get expert help¶
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