6.8.2 Using The NDB Cluster Management Client to Create a Backup

Before starting a backup, make sure that the cluster is properly configured for performing one. (See Section 6.8.3, “Configuration for NDB Cluster Backups”.)

The START BACKUP command is used to create a backup:

START BACKUP [backup_id] [wait_option] [snapshot_option]

wait_option:
WAIT {STARTED | COMPLETED} | NOWAIT

snapshot_option:
SNAPSHOTSTART | SNAPSHOTEND

Successive backups are automatically identified sequentially, so the backup_id, an integer greater than or equal to 1, is optional; if it is omitted, the next available value is used. If an existing backup_id value is used, the backup fails with the error Backup failed: file already exists. If used, the backup_id must follow START BACKUP immediately, before any other options are used.

The wait_option can be used to determine when control is returned to the management client after a START BACKUP command is issued, as shown in the following list:

• If NOWAIT is specified, the management client displays a prompt immediately, as seen here:

  ndb_mgm> START BACKUP NOWAIT
  ndb_mgm>

  In this case, the management client can be used even while it prints progress information from the backup process.

• With WAIT STARTED the management client waits until the backup has started before returning control to the user, as shown here:

  ndb_mgm> START BACKUP WAIT STARTED
  Waiting for started, this may take several minutes
  Node 2: Backup 3 started from node 1
  ndb_mgm>

• WAIT COMPLETED causes the management client to wait until the backup process is complete before returning control to the user.

WAIT COMPLETED is the default.

A snapshot_option can be used to determine whether the backup matches the state of the cluster when START BACKUP was issued, or when it was completed. SNAPSHOTSTART causes the backup to match the state of the cluster when the backup began; SNAPSHOTEND causes the backup to reflect the state of the cluster when the backup was finished. SNAPSHOTEND is the default, and matches the behavior found in previous NDB Cluster releases.

Note

If you use the SNAPSHOTSTART option with START BACKUP, and the CompressedBackup parameter is enabled, only the data and control files are compressed—the log file is not compressed.

If both a wait_option and a snapshot_option are used, they may be specified in either order. For example, all of the following commands are valid, assuming that there is no existing backup having 4 as its ID:

START BACKUP WAIT STARTED SNAPSHOTSTART
START BACKUP SNAPSHOTSTART WAIT STARTED
START BACKUP 4 WAIT COMPLETED SNAPSHOTSTART
START BACKUP SNAPSHOTEND WAIT COMPLETED
START BACKUP 4 NOWAIT SNAPSHOTSTART

The procedure for creating a backup consists of the following steps:

1. Start the management client (ndb_mgm), if it not running already.

2. Execute the START BACKUP command. This produces several lines of output indicating the progress of the backup, as shown here:

   ndb_mgm> START BACKUP
   Waiting for completed, this may take several minutes
   Node 2: Backup 1 started from node 1
   Node 2: Backup 1 started from node 1 completed
    StartGCP: 177 StopGCP: 180
    #Records: 7362 #LogRecords: 0
    Data: 453648 bytes Log: 0 bytes
   ndb_mgm>

3. When the backup has started the management client displays this message:

   Backup backup_id started from node node_id

   backup_id is the unique identifier for this particular backup. This identifier is saved in the cluster log, if it has not been configured otherwise. node_id is the identifier of the management server that is coordinating the backup with the data nodes. At this point in the backup process the cluster has received and processed the backup request. It does not mean that the backup has finished. An example of this statement is shown here:

   Node 2: Backup 1 started from node 1

4. The management client indicates with a message like this one that the backup has started:

   Backup backup_id started from node node_id completed

   As is the case for the notification that the backup has started, backup_id is the unique identifier for this particular backup, and node_id is the node ID of the management server that is coordinating the backup with the data nodes. This output is accompanied by additional information including relevant global checkpoints, the number of records backed up, and the size of the data, as shown here:

   Node 2: Backup 1 started from node 1 completed
    StartGCP: 177 StopGCP: 180
    #Records: 7362 #LogRecords: 0
    Data: 453648 bytes Log: 0 bytes

It is also possible to perform a backup from the system shell by invoking ndb_mgm with the -e or --execute option, as shown in this example:

$> ndb_mgm -e "START BACKUP 6 WAIT COMPLETED SNAPSHOTSTART"

When using START BACKUP in this way, you must specify the backup ID.

Cluster backups are created by default in the BACKUP subdirectory of the DataDir on each data node. This can be overridden for one or more data nodes individually, or for all cluster data nodes in the config.ini file using the BackupDataDir configuration parameter. The backup files created for a backup with a given backup_id are stored in a subdirectory named BACKUP-backup_id in the backup directory.

Cancelling backups.  To cancel or abort a backup that is already in progress, perform the following steps:

1. Start the management client.

2. Execute this command:

   ndb_mgm> ABORT BACKUP backup_id

   The number backup_id is the identifier of the backup that was included in the response of the management client when the backup was started (in the message Backup backup_id started from node management_node_id).

3. The management client acknowledges the abort request with Abort of backup backup_id ordered.

   Note

   At this point, the management client has not yet received a response from the cluster data nodes to this request, and the backup has not yet actually been aborted.

4. After the backup has been aborted, the management client reports this fact in a manner similar to what is shown here:

   Node 1: Backup 3 started from 5 has been aborted.
     Error: 1321 - Backup aborted by user request: Permanent error: User defined error
   Node 3: Backup 3 started from 5 has been aborted.
     Error: 1323 - 1323: Permanent error: Internal error
   Node 2: Backup 3 started from 5 has been aborted.
     Error: 1323 - 1323: Permanent error: Internal error
   Node 4: Backup 3 started from 5 has been aborted.
     Error: 1323 - 1323: Permanent error: Internal error

   In this example, we have shown sample output for a cluster with 4 data nodes, where the sequence number of the backup to be aborted is 3, and the management node to which the cluster management client is connected has the node ID 5. The first node to complete its part in aborting the backup reports that the reason for the abort was due to a request by the user. (The remaining nodes report that the backup was aborted due to an unspecified internal error.)

   Note

   There is no guarantee that the cluster nodes respond to an ABORT BACKUP command in any particular order.

   The Backup backup_id started from node management_node_id has been aborted messages mean that the backup has been terminated and that all files relating to this backup have been removed from the cluster file system.

It is also possible to abort a backup in progress from a system shell using this command:

$> ndb_mgm -e "ABORT BACKUP backup_id"

Note

If there is no backup having the ID backup_id running when an ABORT BACKUP is issued, the management client makes no response, nor is it indicated in the cluster log that an invalid abort command was sent.