add process {--processhosts=|-R }process_host_list
    [--set=attribute_assignment_list] [--verbose | -v] [--sequential-restart] cluster_name

process_host_list:
    process_name[:node_id]@host[,process_name@host[,...]]

process_name:
    {ndb_mgmd|ndbd|ndbmtd|mysqld|ndbapi}

attribute_assignment_list:
    attribute_assignment[,attribute_assignment][,...]

attribute_assignment:
    attribute_name:process_name[=value]

This command adds to an existing cluster one or more processes, which are specified using a process_host_list with the --processhosts option, the format of which is the same as that used with the create cluster command. Any hosts referenced in the list must be members of the site to which the cluster belongs. In addition, all hosts must be resolvable.

For example, the following add process command adds two mysqld processes on hosts tonfisk and flundra to the cluster named mycluster:

mcm> add process --processhosts=mysqld@tonfisk,mysqld@flundra mycluster;
+------------------------------+
| Command result               |
+------------------------------+
| Processes added successfully |
+------------------------------+
1 row in set (2 min 10.39 sec)

With the --verbose option, the command shows an updated process list, after the new processes have been added:

mcm> add process --processhosts=ndbmtd@tonfisk,ndbmtd@flundra --verbose mycluster;
+--------+----------+---------+
| NodeId | Name     | Host    |
+--------+----------+---------+
| 49     | ndb_mgmd | tonfisk |
| 53     | ndb_mgmd | flundra |
| 1      | ndbmtd   | tonfisk |
| 2      | ndbmtd   | flundra |
| 3      | ndbmtd   | tonfisk |
| 4      | ndbmtd   | flundra |
| 50     | mysqld   | tonfisk |
| 51     | mysqld   | flundra |
| 52     | ndbapi   | *       |
+--------+----------+---------+
9 rows in set (2 min 7.57 sec)

You can also manually assign a node ID to the new process you are adding to the cluster by adding “:node_ID.” after the process_name. You are still recommended to follow the best practice of reserving node ID 1 to 144 for data nodes. The following command adds two ndbd processes with node IDs 10 and 11 on hosts tonfisk and flundra, respectively, to mycluster:

mcm> add process --processhosts=ndbd:10@tonfisk,ndbd:11@flundra mycluster;
+------------------------------+
| Command result               |
+------------------------------+
| Processes added successfully |
+------------------------------+
1 row in set (2 min 13.40 sec)

If the cluster is not running when you run the add process command, it is recommended that you start all the new processes added by this command together using the start process --added command or start them together with the whole cluster using the start cluster command—besides starting the nodes, either of the two commands also initializes the added nodes and causes new cluster nodegroups to be formed by issuing a CREATE NODEGROUP command to the cluster. If the added nodes are started with start process --initial instead, you are then required to run CREATE NODEGROUP manually via the ndb_mgm client.

If the cluster is running when you run the add process command, a rolling restart for the cluster is performed at the end of the add process command. Use the --sequential-restart option to make the rolling restart a sequential one.

Adding Free Processes

Using the add process command, you can add unmanaged mysqld processes, or ndbapi slots for ndbapi applications such as ndb_restore. To add an unmanaged mysqld process, prefix the hostname with the wildcard * (asterisk character):

mcm> add process --processhosts=mysqld@*tonfisk,mysqld@*flundra mycluster;
+------------------------------+
| Command result               |
+------------------------------+
| Processes added successfully |
+------------------------------+
1 row in set (2 min 3.14 sec)

To allow the unmanaged mysqld nodes to connect from any host, use the wildcard * (asterisk character) in place of the hostname or IP address:

mcm> add process --processhosts=mysqld@*,mysqld@* mycluster;
+------------------------------+
| Command result               |
+------------------------------+
| Processes added successfully |
+------------------------------+
1 row in set (2 min 3.14 sec)

The same applies to ndbapi slots for ndbapi applications such as ndb_restore: prefix the hostname with the wildcard character to limit connectivity to a specific host, or use only a wildcard, without hostname, to allow ndbapi applications from any host:

mcm> add process --processhosts=ndbapi@*tonfisk,ndbapi@* mycluster;
+------------------------------+
| Command result               |
+------------------------------+
| Processes added successfully |
+------------------------------+
1 row in set (2 min 8.13 sec)

Because “free” processes are not managed by MySQL Cluster Manager, there is no need to run the start process --added command after they have been successfully added to the cluster.

Using add process to Simplify create cluster Commands

Processes added before the cluster is started for the first time are started with the cluster. This makes it possible to use this command to break down what would otherwise be very long create cluster commands. Consider the following set of commands that creates and then starts a cluster named mycluster:

create cluster --processhosts=ndb_mgmd@host1,ndbd@host1,ndbd@host2, \
  mysqld@host3,mysqld@host4 mycluster;
start cluster mycluster;

The long create cluster command can be divided into a shorter (and more manageable) version of itself, plus several add process commands. This set of commands performs the same task as the previous set, creating mycluster with exactly the same processes and hosts as before, and then starting it:

create cluster --processhosts=ndb_mgmd@host1 mycluster;
add process --processhosts=ndbd@host1,ndbd@host2 mycluster;
add process --processhosts=mysqld@host3,mysqld@host4 mycluster;
start cluster mycluster;

Notice that a process that is added to a cluster that was created using create cluster --import and before the import takes place is added with status import, which means it cannot be started or stopped using start process or stop process before an import has taken place.

Configuring a New Process when Adding it

A newly added process inherits its configuration attribute settings from those in effect for its process type on the parent cluster, or assume the default settings for that process type if none apply. Existing attribute settings in the cluster must have process-level scope to be inherited by new processes added later; instance-level settings set for existing process instances prior to adding any new ones do not apply to any of the added processes. (See Configuration attributes, for more information about the scope of attribute settings.)

Inherited attribute settings can be overridden when adding processes; to do this, use the add process command's --set option. This option takes as its argument an attribute assignment list similar in format to that used with the get and set commands. Suppose that the current ndbd process-level setting in the cluster named mycluster for the DataDir attribute is /home/users/ndb/cluster-data, but you wish to add two new ndbd processes that use /tmp/cluster/data instead. You can do this using the following command:

mcm> add process --set=ndbd:DataDir=/tmp/cluster/data
   > --processhosts=mysqld@tonfisk,mysqld@flundra
   > mycluster;

When setting attributes this way, which involves specifying paths for processes running on Windows, you must replace any backslashes (\) used with forward slashes (/), just as with the set command. See Setting Attributes Containing Paths on Windows, for more information.

After a process has been added using add process, you can also use the set command to modify its configuration attribute settings (or specify additional ones) as you would with any other cluster process being managed with MySQL Cluster Manager.