This section provides general information about the behavior of and current limitations in adding MySQL Cluster nodes online.
Redistribution of Data.
The ability to add new nodes online includes a means to
NDBCLUSTER table data
and indexes so that they are distributed across all data
nodes, including the new ones, by means of the
ONLINE TABLE ... REORGANIZE PARTITION statement.
Table reorganization of both in-memory and Disk Data tables is
supported. This redistribution does not currently include
unique indexes (only ordered indexes are redistributed). Prior
to MySQL Cluster NDB 7.2.14,
data is also not redistributed using this method (Bug
The redistribution for
tables already existing before the new data nodes were added is
not automatic, but can be accomplished using simple SQL
statements in mysql or another MySQL client
application. However, all data and indexes added to tables
created after a new node group has been added are distributed
automatically among all cluster data nodes, including those
added as part of the new node group.
Partial starts. It is possible to add a new node group without all of the new data nodes being started. It is also possible to add a new node group to a degraded cluster—that is, a cluster that is only partially started, or where one or more data nodes are not running. In the latter case, the cluster must have enough nodes running to be viable before the new node group can be added.
Effects on ongoing operations.
Normal DML operations using MySQL Cluster data are not
prevented by the creation or addition of a new node group, or
by table reorganization. However, it is not possible to
perform DDL concurrently with table reorganization—that
is, no other DDL statements can be issued while an
ALTER TABLE ...
REORGANIZE PARTITION statement is executing. In
addition, during the execution of
ALTER TABLE ...
REORGANIZE PARTITION (or the execution of any other
DDL statement), it is not possible to restart cluster data
Failure handling. Failures of data nodes during node group creation and table reorganization are handled as hown in the following table:
|Failure occurs during:||Failure occurs in:|
|“Old” data nodes||“New” data nodes||System|
|Node group creation||
Dropping node groups.
The ndb_mgm client supports a
NODEGROUP command, but it is possible to drop a node
group only when no data nodes in the node group contain any
data. Since there is currently no way to “empty”
a specific data node or node group, this command works only
the following two cases:
TRUNCATE TABLE does not work
for this purpose because the data nodes continue to store
the table definitions.
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