17.1.6.10. Limitations Relating to Multiple MySQL Cluster Nodes

Multiple SQL nodes. The following are issues relating to the use of multiple MySQL servers as MySQL Cluster SQL nodes, and are specific to the NDBCLUSTER storage engine:

No distributed table locks. A LOCK TABLES works only for the SQL node on which the lock is issued; no other SQL node in the cluster "sees" this lock. This is also true for a lock issued by any statement that locks tables as part of its operations. (See next item for an example.)
ALTER TABLE operations. ALTER TABLE is not fully locking when running multiple MySQL servers (SQL nodes). (As discussed in the previous item, MySQL Cluster does not support distributed table locks.)

Multiple management nodes. When using multiple management servers:

You must give nodes explicit IDs in connect strings because automatic allocation of node IDs does not work across multiple management servers.
When a management server starts, it first checks for any other management server in the same MySQL Cluster, and upon successful connection to the other management server uses its configuration data. This means that the management server --reload and --initial startup options are ignored unless the management server is the only one running. It also means that, when performing a rolling restart of a MySQL Cluster with multiple management nodes, the management server reads its own configuration file if (and only if) it is the only management server running in this MySQL Cluster. See Section 17.5.5, "Performing a Rolling Restart of a MySQL Cluster", for more information.

Multiple network addresses. Multiple network addresses per data node are not supported. Use of these is liable to cause problems: In the event of a data node failure, an SQL node waits for confirmation that the data node went down but never receives it because another route to that data node remains open. This can effectively make the cluster inoperable.

Note

It is possible to use multiple network hardware interfaces (such as Ethernet cards) for a single data node, but these must be bound to the same address. This also means that it not possible to use more than one [tcp] section per connection in the config.ini file. See Section 17.3.2.8, "MySQL Cluster TCP/IP Connections", for more information.