21.6.9 NDB Cluster Backups With NDB Cluster Replication
This section discusses making backups and restoring from them using NDB Cluster replication. We assume that the replication servers have already been configured as covered previously (see Section 21.6.5, “Preparing the NDB Cluster for Replication”, and the sections immediately following). This having been done, the procedure for making a backup and then restoring from it is as follows:
There are two different methods by which the backup may be started.
Method A. This method requires that the cluster backup process was previously enabled on the source server, prior to starting the replication process. This can be done by including the following line in a
[mysql_cluster]section in the
my.cnf file, where
management_hostis the IP address or host name of the
NDBmanagement server for the source cluster, and
portis the management server's port number:
The port number needs to be specified only if the default port (1186) is not being used. See Section 21.2.5, “Initial Configuration of NDB Cluster”, for more information about ports and port allocation in NDB Cluster.
shellS> ndb_mgm -e "START BACKUP"
Method B. If the
my.cnffile does not specify where to find the management host, you can start the backup process by passing this information to the
NDBmanagement client as part of the
START BACKUPcommand. This can be done as shown here, where
portare the host name and port number of the management server:
shellS> ndb_mgm management_host:port -e "START BACKUP"
In our scenario as outlined earlier (see Section 21.6.5, “Preparing the NDB Cluster for Replication”), this would be executed as follows:
shellS> ndb_mgm rep-source:1186 -e "START BACKUP"
Copy the cluster backup files to the replica that is being brought on line. Each system running an ndbd process for the source cluster will have cluster backup files located on it, and all of these files must be copied to the replica to ensure a successful restore. The backup files can be copied into any directory on the computer where the replica's management host resides, as long as the MySQL and NDB binaries have read permissions in that directory. In this case, we assume that these files have been copied into the directory
While it is not necessary that the replica cluster have the same number of ndbd processes (data nodes) as the source, it is highly recommended this number be the same. It is necessary that the replica be started with the
--skip-slave-startoption, to prevent premature startup of the replication process.
Create any databases on the replica cluster that are present on the source cluster and that are to be replicated.
Reset the replica cluster using this statement in the mysql client:
mysqlR> RESET SLAVE;
You can now start the cluster restoration process on the replica using the ndb_restore command for each backup file in turn. For the first of these, it is necessary to include the
-moption to restore the cluster metadata, as shown here:
shellR> ndb_restore -c replica_host:port -n node-id \ -b backup-id -m -r dir
diris the path to the directory where the backup files have been placed on the replica. For the ndb_restore commands corresponding to the remaining backup files, the
-moption should not be used.
For restoring from a source cluster with four data nodes (as shown in the figure in Section 21.6, “NDB Cluster Replication”) where the backup files have been copied to the directory
/var/BACKUPS/BACKUP-1, the proper sequence of commands to be executed on the replica might look like this:
shellR> ndb_restore -c replica-host:1186 -n 2 -b 1 -m \ -r ./var/BACKUPS/BACKUP-1 shellR> ndb_restore -c replica-host:1186 -n 3 -b 1 \ -r ./var/BACKUPS/BACKUP-1 shellR> ndb_restore -c replica-host:1186 -n 4 -b 1 \ -r ./var/BACKUPS/BACKUP-1 shellR> ndb_restore -c replica-host:1186 -n 5 -b 1 -e \ -r ./var/BACKUPS/BACKUP-1Important
--restore-epoch) option in the final invocation of ndb_restore in this example is required to make sure that the epoch is written to the replica's
mysql.ndb_apply_statustable. Without this information, the replica cannot synchronize properly with the source. (See Section 21.4.24, “ndb_restore — Restore an NDB Cluster Backup”.)
Now you need to obtain the most recent epoch from the
ndb_apply_statustable on the replica (as discussed in Section 21.6.8, “Implementing Failover with NDB Cluster Replication”):
mysqlR> SELECT @latest:=MAX(epoch) FROM mysql.ndb_apply_status;
@latestas the epoch value obtained in the previous step, you can obtain the correct starting position
@posin the correct binary log file
mysql.ndb_binlog_indextable on the source using the query shown here:
mysqlS> SELECT -> @file:=SUBSTRING_INDEX(File, '/', -1), -> @pos:=Position -> FROM mysql.ndb_binlog_index -> WHERE epoch >= @latest -> ORDER BY epoch ASC LIMIT 1;
In the event that there is currently no replication traffic, you can get this information by running
SHOW MASTER STATUSon the source and using the value shown in the
Positioncolumn of the output for the file whose name has the suffix with the greatest value for all files shown in the
Filecolumn. In this case, you must determine which file this is and supply the name in the next step manually or by parsing the output with a script.
mysqlR> CHANGE MASTER TO -> MASTER_LOG_FILE='@file', -> [email protected];
Now that the replica knows from what point in which binary log file to start reading data from the source, you can cause the replica to begin replicating with this statement:
mysqlR> START SLAVE;
To perform a backup and restore on a second replication channel, it is necessary only to repeat these steps, substituting the host names and IDs of the secondary source and replica for those of the primary source and replica servers where appropriate, and running the preceding statements on them.
For additional information on performing Cluster backups and restoring Cluster from backups, see Section 21.5.8, “Online Backup of NDB Cluster”.