Setting up a Replica (mariadb-backup)

Initialize a replication slave using a backup. This guide shows how to use mariadb-backup to provision a new replica from a master server.

The terms master and slave have historically been used in replication, and MariaDB has begun the process of adding primary and replica synonyms. The old terms will continue to be used to maintain backward compatibility - see MDEV-18777 to follow progress on this effort.

mariadb-backup was previously called mariabackup.

This page documents how to set up a replica from a backup.

If you are using MariaDB Galera Cluster, then you may want to try one of the following pages instead:

• Configuring MariaDB Replication between MariaDB Galera Cluster and MariaDB Server

• Configuring MariaDB Replication between Two MariaDB Galera Clusters

For a complete list of mariadb-backup options, see this page.

For a detailed description of mariadb-backup functionality, see this page.

Back up the Database and Prepare it

The first step is to simply take and prepare a fresh full backup of a database server in the replication topology. If the source database server is the desired replication primary, then we do not need to add any additional options when taking the full backup. For example:

$ mariadb-backup --backup \
   --target-dir=/var/mariadb/backup/ \
   --user=mariadb-backup --password=mypassword

If the source database server is a replica of the desired primary, then we should add the --slave-info option, and possibly the --safe-slave-backup option. For example:

$ mariadb-backup --backup \
   --slave-info --safe-slave-backup \
   --target-dir=/var/mariadb/backup/ \
   --user=mariadb-backup --password=mypassword

And then we would prepare the backup as you normally would. For example:

$ mariadb-backup --prepare \
   --target-dir=/var/mariadb/backup/

Copy the Backup to the New Replica

Once the backup is done and prepared, we can copy it to the new replica. For example:

$ rsync -avP /var/mariadb/backup dbserver2:/var/mariadb/backup

Restore the Backup on the New Replica

At this point, we can restore the backup to the datadir, as you normally would. For example:

$ mariadb-backup --copy-back \
   --target-dir=/var/mariadb/backup/

And adjusting file permissions, if necessary:

$ chown -R mysql:mysql /var/lib/mysql/

Create a Replication User on the Primary

Before the new replica can begin replicating from the primary, we need to create a user account on the primary that the replica can use to connect, and we need to grant the user account the REPLICATION SLAVE privilege. For example:

CREATE USER 'repl'@'dbserver2' IDENTIFIED BY 'password';
GRANT REPLICATION SLAVE ON *.*  TO 'repl'@'dbserver2';

Configure the New Replica

Before we start the server on the new replica, we need to configure it. At the very least, we need to ensure that it has a unique server_id value. We also need to make sure other replication settings are what we want them to be, such as the various GTID system variables, if those apply in the specific environment.

Once configuration is done, we can start the MariaDB Server process on the new replica.

Start Replication on the New Replica

At this point, we need to get the replication coordinates of the primary from the original backup directory.

If we took the backup on the primary, then the coordinates are in the xtrabackup_binlog_info file. If we took the backup on another replica and if we provided the --slave-info option, then the coordinates are in the file xtrabackup_slave_info file.

mariadb-backup dumps replication coordinates in two forms: GTID coordinates and binary log file and position coordinates, like the ones you would normally see from SHOW MASTER STATUS output. We can choose which set of coordinates we would like to use to set up replication.

For example:

mariadb-bin.000096 568 0-1-2

Regardless of the coordinates we use, we will have to set up the primary connection using CHANGE MASTER TO and then start the replication threads with START SLAVE.

GTIDs

If we want to use GTIDs, then we will have to first set gtid_slave_pos to the GTID coordinates that we pulled from either the xtrabackup_binlog_info file or the xtrabackup_slave_info file in the backup directory. For example:

$ cat xtrabackup_binlog_info
mariadb-bin.000096 568 0-1-2

And then we would set MASTER_USE_GTID=slave_pos in the CHANGE MASTER TO statement. For example:

SET GLOBAL gtid_slave_pos = "0-1-2";
CHANGE MASTER TO 
   MASTER_HOST="dbserver1", 
   MASTER_PORT=3306, 
   MASTER_USER="repl",  
   MASTER_PASSWORD="password", 
   MASTER_USE_GTID=slave_pos;
START SLAVE;

File and Position

If we want to use the binary log file and position coordinates, then we would set MASTER_LOG_FILE and MASTER_LOG_POS in the CHANGE MASTER TO statement to the file and position coordinates that we pulled; either the xtrabackup_binlog_info file or the xtrabackup_slave_info file in the backup directory, depending on whether the backup was taken from the primary or from a replica of the primary. For example:

CHANGE MASTER TO 
   MASTER_HOST="dbserver1", 
   MASTER_PORT=3306, 
   MASTER_USER="repl",  
   MASTER_PASSWORD="password", 
   MASTER_LOG_FILE='mariadb-bin.000096',
   MASTER_LOG_POS=568;
START SLAVE;

Check the Status of the New Replica

We should be done setting up the replica now, so we should check its status with SHOW SLAVE STATUS. For example:

SHOW SLAVE STATUS\G

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