21.7.9 NDB Cluster Backups With NDB Cluster Replication (original) (raw)

21.7.9 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 (seeSection 21.7.5, “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 themy.cnf file, where_managementhost_ is the IP address or host name of theNDB management server for the source cluster, and port is the management server's port number:

   ndb-connectstring=management_host[:port]  

   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 theNDB management client as part of the START BACKUP command. This can be done as shown here, where managementhost 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 (seeSection 21.7.5, “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 anndbd 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 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-start option, to prevent premature startup of the replication process.
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 (orCREATE 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 themysql client:

mysqlR> RESET SLAVE;  

1. 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 inSection 21.7, “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  

1. Now you need to obtain the most recent epoch from thendb_apply_status table on the replica (as discussed inSection 21.7.8, “Implementing Failover with NDB Cluster Replication”):

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

1. 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 themysql.ndb_binlog_index table on the source. The query shown here gets these from thenext_position andnext_file columns from the last epoch applied before the logical restore position:

mysqlS> SELECT  
     ->     @file:=SUBSTRING_INDEX(next_file, '/', -1),  
     ->     @pos:=next_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 runningSHOW MASTER STATUS on the source and using the value shown in thePosition 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 CHANGE MASTER TO statement in the replica'smysql client:

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

1. 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, seeSection 21.6.8, “Online Backup of NDB Cluster”.