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MySQL 5.1 Reference Manual :: 20 MySQL Cluster :: 20.14 Known Limitations of MySQL Cluster :: 20.14.10 Limitations Relating to Multiple Cluster Nodes
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20.14.10. Limitations Relating to Multiple 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.)

  • DDL operations.  DDL operations (such as CREATE TABLE or ALTER TABLE) are not safe from data node failures. If a data node fails while trying to peform one of these, the data dictionary is locked and no further DDL statements can be executed without restarting the cluster.

Multiple management nodes.  When using multiple management servers:

  • You must give nodes explicit IDs in connectstrings because automatic allocation of node IDs does not work across multiple management servers.

  • You must take extreme care to have the same configurations for all management servers. No special checks for this are performed by the cluster.

Multiple data node processes.  While it is possible to run multiple cluster processes concurrently on a single host, it is not always advisable to do so for reasons of performance and high availability, as well as other considerations. In particular, in MySQL 5.1 and MySQL Cluster NDB 6.x, we do not support for production use any MySQL Cluster deployment in which more than one ndbd process is run on a single physical machine.

Note

We may support multiple data nodes per host in a future MySQL release, following additional testing. However, in current versions of MySQL Cluster, such configurations can be considered experimental only.

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 20.3.4.7, “Cluster TCP/IP Connections”, for more information.