7.9 NDB Cluster Backups With NDB Cluster Replication

7.9.1 NDB Cluster Replication: Automating Synchronization of the Replica to the Source Binary Log

7.9.2 Point-In-Time Recovery Using 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 7.5, “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:

1. 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_host is the IP address or host name of the NDB management server for the source cluster, and port is the management server's port number:

     ndb-connectstring=management_host[:port]

     Note

     The port number needs to be specified only if the default port (1186) is not being used. See Section 3.3, “Initial Configuration of NDB Cluster”, for more information about ports and port allocation in NDB Cluster.

     In this case, the backup can be started by executing this statement on the replication source:

     shellS> ndb_mgm -e "START BACKUP"

   • Method B.  If the my.cnf file does not specify where to find the management host, you can start the backup process by passing this information to the NDB management client as part of the START BACKUP command. This can be done as shown here, where management_host and port are 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 7.5, “Preparing the NDB Cluster for Replication”), this would be executed as follows:

     shellS> ndb_mgm rep-source:1186 -e "START BACKUP"

2. Copy the cluster backup files to the replica that is being brought on line. Each system running an ndbd process for the source cluster has 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 /var/BACKUPS/BACKUP-1.

   While it is not necessary that the replica cluster have the same number of data nodes as the source, it is highly recommended this number be the same. It is necessary that the replication process is prevented from starting when the replica server starts. You can do this by starting the replica with the --skip-slave-start option on the command line, by including skip-slave-start in the replica's my.cnf file, or in NDB 8.0.24 or later, by setting the skip_slave_start system variable.

3. Create any databases on the replica cluster that are present on the source cluster and that are to be replicated.

   Important

   A CREATE DATABASE (or CREATE SCHEMA) statement corresponding to each database to be replicated must be executed on each SQL node in the replica cluster.

4. Reset the replica cluster using this statement in the mysql client:

   mysqlR> RESET SLAVE;

   In NDB 8.0.22 or later, you can also use this statement:

   mysqlR> RESET REPLICA;

5. 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 -m option to restore the cluster metadata, as shown here:

   shellR> ndb_restore -c replica_host:port -n node-id \
           -b backup-id -m -r dir

   dir is 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 -m option should not be used.

   For restoring from a source cluster with four data nodes (as shown in the figure in Chapter 7, 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-1

   Important

   The -e (or --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_status table. Without this information, the replica cannot synchronize properly with the source. (See Section 5.23, “ndb_restore — Restore an NDB Cluster Backup”.)

6. Now you need to obtain the most recent epoch from the ndb_apply_status table on the replica (as discussed in Section 7.8, “Implementing Failover with NDB Cluster Replication”):

   mysqlR> SELECT @latest:=MAX(epoch)
           FROM mysql.ndb_apply_status;

7. Using @latest as the epoch value obtained in the previous step, you can obtain the correct starting position @pos in the correct binary log file @file from the mysql.ndb_binlog_index table on the source. The query shown here gets these from the Position and File columns from the last epoch applied before the logical restore position:

   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 similar information by running SHOW MASTER STATUS on the source and using the value shown in the Position column of the output for the file whose name has the suffix with the greatest value for all files shown in the File column. 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.

8. Using the values obtained in the previous step, you can now issue the appropriate in the replica's mysql client. In NDB 8.0.23 and later, use the following CHANGE REPLICATION SOURCE TO statement:

   mysqlR> CHANGE REPLICATION SOURCE TO
        ->     SOURCE_LOG_FILE='@file',
        ->     SOURCE_LOG_POS=@pos;

   Prior to NDB 8.0.23, you can must use the CHANGE MASTER TO statement shown here:

   mysqlR> CHANGE MASTER TO
        ->     MASTER_LOG_FILE='@file',
        ->     MASTER_LOG_POS=@pos;

9. 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;

   Beginning with NDB 8.0.22, you can also use the following statement:

   mysqlR> START REPLICA;

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 6.8, “Online Backup of NDB Cluster”.