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 consumed 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:
DELETEstatement on an
NDBtable 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 17.5.5, “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 17.3.3, “MySQL Cluster Configuration Files”. Most configuration parameters can be upgraded online. These hard limits include:
Database memory size and index memory size (
DataMemoryis allocated as 32KB pages. As each
DataMemorypage is used, it is assigned to a specific table; once allocated, this memory cannot be freed except by dropping the table.
See Section 126.96.36.199, “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 parameters
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.
Memory usage. All Cluster table rows are of fixed length. This means (for example) that if a table has one or more
VARCHARfields containing only relatively small values, more memory and disk space is required when using the
NDBstorage engine than would be the case for the same table and data using the
MyISAMengine. (In other words, in the case of a
VARCHARcolumn, the column requires the same amount of storage as a
CHARcolumn of the same size.)
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 to 48, 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 in MySQL 5.0 Cluster is 20320. This limit is hard-coded.