126.96.36.199 Adding NDB Cluster Data Nodes Online: General Issues
This section provides general information about the behavior of and current limitations in adding NDB Cluster nodes online.
Redistribution of Data. The ability to add new nodes online includes a means to reorganize
NDBCLUSTER table data and indexes so that they are distributed across all data nodes, including the new ones, by means of the
ALTER 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).
The redistribution for
NDBCLUSTER 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 NDB 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 nodes.
Failure handling. Failures of data nodes during node group creation and table reorganization are handled as shown in the following table:
Table 21.279 Data node failure handling during node group creation and table reorganization
|Failure during||Failure in “Old” data node||Failure in “New” data node||System Failure|
|Node group creation||
Dropping node groups. The ndb_mgm client supports a
DROP 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 TABLEdoes not work for this purpose because the data nodes continue to store the table definitions.