Manual SST of Galera Cluster Node With mariadb-backup

Sometimes it can be helpful to perform a "manual SST" when Galera's normal SSTs fail. This can be especially useful when the cluster's datadir is very large, since a normal SST can take a long time to fail in that case.

A manual SST essentially consists of taking a backup of the donor, loading the backup on the joiner, and then manually editing the cluster state on the joiner node. This page will show how to perform this process with mariadb-backup.

Process

• Check that the donor and joiner nodes have the same mariadb-backup version.

mariabackup --version

• Create backup directory on donor.

MYSQL_BACKUP_DIR=/mysql_backup
mkdir $MYSQL_BACKUP_DIR

• Take a full backup the of the donor node with mariabackup. The --galera-info option should also be provided, so that the node's cluster state is also backed up.

DB_USER=sstuser
DB_USER_PASS=password
mariabackup --backup  --galera-info \
   --target-dir=$MYSQL_BACKUP_DIR \
   --user=$DB_USER \
   --password=$DB_USER_PASS

• Verify that the MariaDB Server process is stopped on the joiner node. This will depend on your service manager.

For example, on systemd systems, you can execute::

systemctl status mariadb

• Create the backup directory on the joiner node.

MYSQL_BACKUP_DIR=/mysql_backup
mkdir $MYSQL_BACKUP_DIR

• Copy the backup from the donor node to the joiner node.

OS_USER=dba
JOINER_HOST=dbserver2.mariadb.com
rsync -av $MYSQL_BACKUP_DIR/* ${OS_USER}@${JOINER_HOST}:${MYSQL_BACKUP_DIR}

• Prepare the backup on the joiner node.

mariabackup --prepare \
   --target-dir=$MYSQL_BACKUP_DIR

• Get the Galera Cluster version ID from the donor node's grastate.dat file.

MYSQL_DATADIR=/var/lib/mysql
cat $MYSQL_DATADIR/grastate.dat | grep version

For example, a very common version number is "2.1".

• Get the node's cluster state from the xtrabackup_galera_info file in the backup that was copied to the joiner node.

cat $MYSQL_BACKUP_DIR/xtrabackup_galera_info

The file contains the values of the wsrep_local_state_uuid and wsrep_last_committed status variables.

The values are written in the following format:

wsrep_local_state_uuid:wsrep_last_committed

For example:

d38587ce-246c-11e5-bcce-6bbd0831cc0f:1352215

• Create a grastate.dat file in the backup directory of the joiner node. The Galera Cluster version ID, the cluster uuid, and the seqno from previous steps will be used to fill in the relevant fields.

For example, with the example values from the last two steps, we could do:

sudo tee $MYSQL_BACKUP_DIR/grastate.dat <<EOF
# GALERA saved state
version: 2.1
uuid:    d38587ce-246c-11e5-bcce-6bbd0831cc0f
seqno:   1352215
safe_to_bootstrap: 0
EOF

• Remove the existing contents of the datadir on the joiner node.

MYSQL_DATADIR=/var/lib/mysql
rm -Rf $MYSQL_DATADIR/*

• Copy the contents of the backup directory to the datadir the on joiner node.

mariabackup --copy-back \
   --target-dir=$MYSQL_BACKUP_DIR

• Make sure the permissions of the datadir are correct on the joiner node.

chown -R mysql:mysql $MYSQL_DATADIR/

• Start the MariaDB Server process on the joiner node. This will depend on your service manager.

For example, on systemd systems, you can execute::

systemctl start mariadb

• Watch the MariaDB error log on the joiner node and verify that the node does not need to perform a normal SSTs due to the manual SST.

tail -f /var/log/mysql/mysqld.log

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