17.5.2. Commands in the MySQL Cluster Management Client

In addition to the central configuration file, a cluster may also be controlled through a command-line interface available through the management client ndb_mgm. This is the primary administrative interface to a running cluster.

Commands for the event logs are given in Section 17.5.6, "Event Reports Generated in MySQL Cluster"; commands for creating backups and restoring from them are provided in Section 17.5.3, "Online Backup of MySQL Cluster".

The management client has the following basic commands. In the listing that follows, node_id denotes either a database node ID or the keyword ALL, which indicates that the command should be applied to all of the cluster's data nodes.

HELP

Displays information on all available commands.
SHOW

Displays information on the cluster's status. Possible node status values include UNKNOWN, NO_CONTACT, NOT_STARTED, STARTING, STARTED, SHUTTING_DOWN, and RESTARTING. The output from this command also indicates when the cluster is in single user mode (status SINGLE USER MODE).
node_id START

Brings online the data node identified by node_id (or all data nodes).

ALL START works on all data nodes only, and does not affect management nodes.

Important

To use this command to bring a data node online, the data node must have been started using ndbd --nostart or ndbd -n.
node_id STOP [-a] [-f]

Stops the data or management node identified by node_id. Note that ALL STOP works to stop all data nodes only, and does not affect management nodes.

A node affected by this command disconnects from the cluster, and its associated ndbd or ndb_mgmd process terminates.

The -a option causes the node to be stopped immediately, without waiting for the completion of any pending transactions.

Normally, STOP fails if the result would cause an incomplete cluster. The -f option forces the node to shut down without checking for this. If this option is used and the result is an incomplete cluster, the cluster immediately shuts down.

Warning

Use of the -a option also disables the safety check otherwise performed when STOP is invoked to insure that stopping the node does not cause an incomplete cluster. In other words, you should exercise extreme care when using the -a option with the STOP command, due to the fact that this option makes it possible for the cluster to undergo a forced shutdown because it no longer has a complete copy of all data stored in NDB.
node_id RESTART [-n] [-i] [-a] [-f]

Restarts the data node identified by node_id (or all data nodes).

Using the -i option with RESTART causes the data node to perform an initial restart; that is, the node's file system is deleted and recreated. The effect is the same as that obtained from stopping the data node process and then starting it again using ndbd --initial from the system shell. Note that backup files and Disk Data files are not removed when this option is used.

Using the -n option causes the data node process to be restarted, but the data node is not actually brought online until the appropriate START command is issued. The effect of this option is the same as that obtained from stopping the data node and then starting it again using ndbd --nostart or ndbd -n from the system shell.

Using the -a causes all current transactions relying on this node to be aborted. No GCP check is done when the node rejoins the cluster.

Normally, RESTART fails if taking the node offline would result in an incomplete cluster. The -f option forces the node to restart without checking for this. If this option is used and the result is an incomplete cluster, the entire cluster is restarted.
node_id STATUS

Displays status information for the data node identified by node_id (or for all data nodes).

The output from this command also indicates when the cluster is in single user mode.
node_id REPORT report-type

Displays a report of type report-type for the data node identified by node_id, or for all data nodes using ALL.

Currently, there are two accepted values for report-type:
- BackupStatus provides a status report on a cluster backup in progress
- MemoryUsage displays how much data memory and index memory is being used by each data node as shown in this example:
```
ndb_mgm> ALL REPORT
                                MEMORYNode 1: Data usage is 5%(177 32K pages of total 3200)Node 1: Index usage is 0%(108 8K pages of total 12832)Node 2: Data usage is 5%(177 32K pages of total 3200)Node 2: Index usage is 0%(108 8K pages of total 12832)
```
  This information is also available from the ndbinfo.memoryusage table.
report-type is case-insensitive and "fuzzy"; for MemoryUsage, you can use MEMORY (as shown in the prior example), memory, or even simply MEM (or mem). You can abbreviate BackupStatus in a similar fashion.
ENTER SINGLE USER MODE node_id

Enters single user mode, whereby only the MySQL server identified by the node ID node_id is permitted to access the database.

Currently, it is not possible for data nodes to join a MySQL Cluster while it is running in single user mode. (Bug #20395)
EXIT SINGLE USER MODE

Exits single user mode, enabling all SQL nodes (that is, all running mysqld processes) to access the database.

Note

It is possible to use EXIT SINGLE USER MODE even when not in single user mode, although the command has no effect in this case.
QUIT, EXIT

Terminates the management client.

This command does not affect any nodes connected to the cluster.
SHUTDOWN

Shuts down all cluster data nodes and management nodes. To exit the management client after this has been done, use EXIT or QUIT.

This command does not shut down any SQL nodes or API nodes that are connected to the cluster.
CREATE NODEGROUP nodeid[, nodeid, ...]

Creates a new MySQL Cluster node group and causes data nodes to join it.

This command is used after adding new data nodes online to a MySQL Cluster, and causes them to join a new node group and thus to begin participating fully in the cluster. The command takes as its sole parameter a comma-separated list of node IDs—these are the IDs of the nodes just added and started that are to join the new node group. The number of nodes must be the same as the number of nodes in each node group that is already part of the cluster (each MySQL Cluster node group must have the same number of nodes). In other words, if the MySQL Cluster has 2 node groups of 2 data nodes each, then the new node group must also have 2 data nodes.

The node group ID of the new node group created by this command is determined automatically, and always the next highest unused node group ID in the cluster; it is not possible to set it manually.

For more information, see Section 17.5.13, "Adding MySQL Cluster Data Nodes Online".
DROP NODEGROUP nodegroup_id

Drops the MySQL Cluster node group with the given nodegroup_id.

This command can be used to drop a node group from a MySQL Cluster. DROP NODEGROUP takes as its sole argument the node group ID of the node group to be dropped.

DROP NODEGROUP acts only to remove the data nodes in the effected node group from that node group. It does not stop data nodes, assign them to a different node group, or remove them from the cluster's configuration. A data node that does not belong to a node group is indicated in the output of the management client SHOW command with no nodegroup in place of the node group ID, like this (indicated using bold text):
```
id=3    @10.100.2.67  (5.6.11-ndb-7.3.3, no
                    nodegroup)
```
Prior to MySQL Cluster NDB 7.0.4, the SHOW output was not updated correctly following DROP NODEGROUP. (Bug #43413)

DROP NODEGROUP works only when all data nodes in the node group to be dropped are completely empty of any table data and table definitions. Since there is currently no way using ndb_mgm or the mysql client to remove all data from a specific data node or node group, this means that the command succeeds only in the two following cases:
1. After issuing CREATE NODEGROUP in the ndb_mgm client, but before issuing any ALTER ONLINE TABLE ... REORGANIZE PARTITION statements in the mysql client.
2. After dropping all NDBCLUSTER tables using DROP TABLE.
  
  TRUNCATE TABLE does not work for this purpose because this removes only the table data; the data nodes continue to store an NDBCLUSTER table's definition until a DROP TABLE statement is issued that causes the table metadata to be dropped.
For more information about DROP NODEGROUP, see Section 17.5.13, "Adding MySQL Cluster Data Nodes Online".