Data backups and restores

The nzreplanalyze, nzreplbackup, and nzreplrestore commands are specialized backup and restore tools that were developed for replication environments. They incorporate the functionality of the NPS® nzbackup and nzrestore commands, with the addition of verification and settings that are required for replication. You can use the NPS commands directly, but you might see error messages that are related to the replication state and user and group restoration, and a restriction applies to the nzbackup command.

nzbackup command

You might see the following message when using the nzbackup command:

Warning: Replication should be suspended while performing synchronized
backup.

The message indicates that replication is still active on the node. If it is a primary node, it might continue to process write transactions. This would make the resulting backup, if you use it to restore to a replica, out of sync with the primary. You can either suspend the primary before running the nzbackup command or use the nzreplbackup command, which suspends the primary as part of the command execution. You can ignore the message if you are backing up the database for non-replication purposes or if you can guarantee that no changes will be made to the replicated databases.

If the message is received on a replica, it indicates that you must suspend the replica to ensure consistency. You might want to take regular backups from the replica, for example, to avoid taking the primary offline for workload processing.

If you take an incremental backup on the primary, by using the -nzbackup command with the -cumulative or -differential option, you cannot apply the backup on the replica.

nzrestore command

You might see a message similar to the following one when using the nzrestore command:

Warning: User and group creation is skipped when restoring to a
replication replica node, or to a non-replicated database on a
primary node.

The message indicates that users and groups are not included in the restore of the database. This is because users and groups are part of the “globals” database in replication.

You might also see a message similar to the following one when using the nzrestore command:

Error: DB SQL 'set enable_restore_mode=1;set enable_dsid_joins=1;set
replicawrite=1;set serializable=0;' failed - DB error - ERROR: SET
REPLICAWRITE TO ON requires replication to be suspended.

To restore a replicated database on a replica node by using the nzrestore command, you must first suspend replication on the replica node and then run the nzrestore command. To change the activation state of the node, use the ALTER REPLICATION NODE command. You cannot use this command to change the state when replication suspension results from the “master continue on error” feature. The error details reflect internal replication settings.

Additional considerations

The NPS nzhostbackup command is incompatible with the replication disaster recovery solution because the command restores the primary host to a previous point in time but the replicas might have processed newer transactions. This results in a fork situation. Instead of using the nzhostbackup command if the primary node is corrupted, promote a replica to the primary role and recover the corrupted node from the new primary.