Variable-length column support.  The NDBCLUSTER storage engine now supports variable-length column types for in-memory tables.

Previously, for example, any Cluster table having one or more VARCHAR fields which contained only relatively small values, much more memory and disk space were required when using the NDBCLUSTER storage engine than would have been the case for the same table and data using the MyISAM engine. In other words, in the case of a VARCHAR column, such a column required the same amount of storage as a CHAR column of the same size. In MySQL 5.1, this is no longer the case for in-memory tables, where storage requirements for variable-length column types such as VARCHAR and BINARY are comparable to those for these column types when used in MyISAM tables (see Section 10.5, “Data Type Storage Requirements”).

Replication with MySQL Cluster.  It is now possible to use MySQL replication with Cluster databases. For details, see Section 17.6, “MySQL Cluster Replication”.

Circular Replication.  Circular replication is also supported with MySQL Cluster, beginning with MySQL 5.1.18. See Section 17.6.10, “MySQL Cluster Replication — Multi-Master and Circular Replication”.

auto_increment_increment and auto_increment_offset.  The auto_increment_increment and auto_increment_offset server system variables are supported for Cluster replication beginning with MySQL 5.1.20, MySQL Cluster NDB 6.2.5, and MySQL Cluster 6.3.2.

Database autodiscovery and online schema changes.  Autodiscovery of databases is now supported for multiple MySQL servers accessing the same MySQL Cluster. Formerly, autodiscovery in MySQL Cluster 5.1 and MySQL Cluster NDB 6.x releases required that a given mysqld was already running and connected to the cluster at the time that the database was created on a different mysqld — in other words, when a mysqld process connected to the cluster after a database named db_name was created, it was necessary to issue a CREATE DATABASE db_name or CREATE SCHEMA db_name statement on the “new” MySQL server when it first accesseed that MySQL Cluster. Beginning with MySQL Cluster NDB 6.2.16 and MySQL Cluster NDB 6.3.18, such a CREATE statement is no longer required. (Bug#39612)

This also means that online schema changes in NDB tables are now possible. That is, the result of operations such as ALTER TABLE and CREATE INDEX performed on one SQL node in the cluster are now visible to the cluster's other SQL nodes without any additional action being taken.

Backup and restore between architectures.  Beginning with MySQL 5.1.10, it is possible to perform a Cluster backup and restore between different architectures. Previously — for example — you could not back up a cluster running on a big-endian platform and then restore from that backup to a cluster running on a little-endian system. (Bug#19255)

Character set directory.  Beginning with MySQL 5.1.10, it is possible to install MySQL with Cluster support to a nondefault location and change the search path for font description files using either the --basedir or --character-sets-dir options. (Previously, ndbd in MySQL 5.1 searched only the default path — typically /usr/local/mysql/share/mysql/charsets — for character sets.)

Multiple management servers.  In MySQL 5.1 (including all MySQL Cluster NDB 6.x versions), it is no longer necessary, when running multiple management servers, to restart all the cluster's data nodes to enable the management nodes to see one another.

Also, when using multiple management servers and starting concurrently several API nodes (possibly including one or more SQL nodes) whose connectstrings listed the management servers in different order, it was possible for 2 API nodes to be assigned the same node ID. This issue is resolved in MySQL Cluster NDB 6.2.17, 6.3.23, and 6.4.3. (Bug#42973)

Multiple data node processes per host.  Beginning with MySQL Cluster NDB 6.2.0, you can use multiple data node processes on a single host. (In MySQL Cluster NDB 6.1, MySQL 5.1, and earlier release series, we did not support production MySQL Cluster deployments in which more than one ndbd process was run on a single physical machine.)

In addition, MySQL Cluster NDB 7.0 introduces support for multi-threaded data nodes (ndbmtd). See Section 17.1.4.5, “MySQL Cluster Development in MySQL Cluster NDB 7.0”, and Section 17.4.3, “ndbmtd — The MySQL Cluster Data Node Daemon (Multi-Threaded)”, for more information.

Identifiers.  Formerly (in MySQL 5.0 and earlier), database names, table names and attribute names could not be as long for NDB tables as tables using other storage engines, because attribute names were truncated internally. In MySQL 5.1 and later, names of MySQL Cluster databases, tables, and table columns follow the same rules regarding length as they do for any other storage engine.

Length of CREATE TABLE statements.  CREATE TABLE statements may be no more than 4096 characters in length. This limitation affects MySQL 5.1.6, 5.1.7, and 5.1.8 only. (See Bug#17813)

IGNORE and REPLACE functionality.  In MySQL 5.1.7 and earlier, INSERT IGNORE, UPDATE IGNORE, and REPLACE were supported only for primary keys, but not for unique keys. It was possible to work around this issue by removing the constraint, then dropping the unique index, performing any inserts, and then adding the unique index again.

This limitation was removed for INSERT IGNORE and REPLACE in MySQL 5.1.8. (See Bug#17431.)

AUTO_INCREMENT columns.  In MySQL 5.1.10 and earlier versions, the maximum number of tables having AUTO_INCREMENT columns — including those belonging to hidden primary keys — was 2048.

This limitation was lifted in MySQL 5.1.11.

Maximum number of cluster nodes.  Prior to MySQL Cluster NDB 6.1.1, the total maximum number of nodes in a MySQL Cluster was 63, including all SQL nodes (MySQL Servers), API nodes (applications accessing the cluster other than MySQL servers), data nodes, and management servers.

Starting with MySQL Cluster NDB 6.1.1, the total maximum number of nodes in a MySQL Cluster is 255, including all SQL nodes (MySQL Servers), API nodes (applications accessing the cluster other than MySQL servers), data nodes, and management servers. The total number of data nodes and management nodes beginning with this version is 63, of which up to 48 can be data nodes.

Recovery of memory from deleted rows.  Beginning with MySQL Cluster NDB 6.3.7, memory can be reclaimed from an NDB table for reuse with any NDB table by employing OPTIMIZE TABLE, subject to the following limitations:

You can regulate the effects of OPTIMIZE on performance by adjusting the value of the global system variable ndb_optimization_delay, which sets the number of milliseconds to wait between batches of rows being processed by OPTIMIZE. The default value is 10 milliseconds. It is possible to set a lower value (to a minimum of 0), but not recommended. The maximum is 100000 milliseconds (that is, 100 seconds).

Implicit Rollbacks.  Prior to MySQL Cluster NDB 6.2.17 and MySQL Cluster NDB 6.3.19, MySQL Cluster did not automtically roll back a transaction that was aborted by a duplicate key or similar error, and subsequent statements raised ERROR 1296 (HY000): Got error 4350 'Transaction already aborted' from NDBCLUSTER. In such cases, it was necessary to issue an explicit ROLLBACK statement first, and then to retry the entire transaction.

Beginning with MySQL Cluster NDB 6.2.17 and MySQL Cluster NDB 6.3.19, this limitation has been removed; now, an error which causes a transaction to be aborted generates an implicit rollback of the entire transaction. This is logged with the warning Storage engine NDB does not support rollback for this statement. Transaction rolled back and must be restarted. A statement subsequent to this starts a new transaction. (Bug#32656)

Number of tables.  Previously, the maximum number of NDBCLUSTER tables in a single MySQL Cluster was 1792, but this is no longer the case in MySQL 5.1 and later MySQL Cluster releases. However, the number of tables is still included in the total maximum number of NDBCLUSTER database objects (20320). (See Section 17.1.5.5, “Limits Associated with Database Objects in MySQL Cluster”.)

DDL operations.  Beginning with MySQL Cluster NDB 6.4.0, DDL operations (such as CREATE TABLE or ALTER TABLE) are protected from data node failures. Previously, if a data node failed while trying to perform one of these, the data dictionary became locked and no further DDL statements could be executed without restarting the cluster (Bug#36718).

Adding and dropping of data nodes.  In MySQL Cluster NDB 6.3 and previous versions of MySQL Cluster, the online adding or dropping of data nodes was not possible; such operations required a complete shutdown and restart of the entire cluster. In MySQL Cluster NDB 7.0 (beginning with MySQL Cluster NDB 6.4.0) and later MySQL Cluster release series, it is possible to add new data nodes to a running MySQL Cluster by performing a rolling restart, so that the cluster and the data stored in it remain available to applications.

When planning to increase the number of data nodes in the cluster online in MySQL Cluster NDB 7.0 or MySQL Cluster NDB 7.1, you should be aware of and take into account the following issues:

For more information, see Section 17.5.11, “Adding MySQL Cluster Data Nodes Online”.

Native support for default column values.  Starting with MySQL Cluster NDB 7.1.0, default values for table columns are stored by NDBCLUSTER, rather than by the MySQL server as was previously the case. Because less data must be sent from an SQL node to the data nodes, inserts on tables having column value defaults can be performed more efficiently than before.

Tables created using previous MySQL Cluster releases can still be used in MySQL Cluster 7.1.0 and later, although they do not support native default values and continue to use defaults supplied by the MySQL server until they are upgraded. This can be done by means of an offline ALTER TABLE statement.