In this section, we list limits found in MySQL Cluster that either differ from limits found in, or that are not found in, standard MySQL.
Memory usage and recovery.
Memory comsumed when data is inserted into an
NDB table is not automatically
recovered when deleted, as it is with other storage engines.
Instead, the following rules hold true:
DELETE statement on an
NDB table makes the memory
formerly used by the deleted rows available for re-use by
inserts on the same table only. However, this memory can be
made available for general re-use by performing a rolling
restart of the cluster. See
Section 188.8.131.52, “Performing a Rolling Restart of a MySQL Cluster”.
Limits imposed by the cluster's configuration. A number of hard limits exist which are configurable, but available main memory in the cluster sets limits. See the complete list of configuration parameters in Section 15.3.2, “MySQL Cluster Configuration Files”. Most configuration parameters can be upgraded online. These hard limits include:
Database memory size and index memory size
DataMemory is allocated as 32KB
pages. As each
DataMemory page is
used, it is assigned to a specific table; once
allocated, this memory cannot be freed except by
dropping the table.
See Section 184.108.40.206, “Defining MySQL Cluster Data Nodes”, for
further information about
The maximum number of operations that can be performed
per transaction is set using the configuration
Different limits related to tables and indexes. For
example, the maximum number of ordered indexes in the
cluster is determined by
MaxNoOfOrderedIndexes, and the
maximum number of ordered inexes per table is 16.
All Cluster table rows are of fixed length. This means
(for example) that if a table has one or more
VARCHAR fields containing
only relatively small values, more memory and disk space
is required when using the
NDB storage engine than would
be the case for the same table and data using the
MyISAM engine. (In other words, in the
case of a
the column requires the same amount of storage as a
CHAR column of the same
Node and data object maximums. The following limits apply to numbers of cluster nodes and metadata objects:
The maximum number of data nodes is 48.
A data node must have a node ID in the range of 1‐49, inclusive. (Management and API nodes may use any integer in the range of 1‐63 inclusive as a node ID.)
The total maximum number of nodes in a MySQL Cluster is 63. This number includes all SQL nodes (MySQL Servers), API nodes (applications accessing the cluster other than MySQL servers), data nodes, and management servers.
The maximum number of metadata objects is limited to
1600, including database tables, system tables, indexes