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.
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
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.)
If any of the management servers are running on the same host, you must give nodes explicit IDs in connection strings because automatic allocation of node IDs does not work across multiple management servers on the same host. This is not required if every management server resides on a different host.
In MySQL Cluster NDB 7.0.7 and earlier, you must take extreme care to have the same configurations for all management servers; no special checks for consistency are performed.
Beginning with MySQL Cluster NDB 7.0.8, a management server
when first starting 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
--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
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.
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 220.127.116.11, “MySQL Cluster TCP/IP Connections”, for more