Oracle 5.0 Reference Manual page 1535

MySQL Cluster Overview
A MySQL Cluster consists of a set of computers, known as hosts, each running one or more
processes. These processes, known as nodes, may include MySQL servers (for access to NDB data),
data nodes (for storage of the data), one or more management servers, and possibly other specialized
data access programs. The relationship of these components in a MySQL Cluster is shown here:
All these programs work together to form a MySQL Cluster (see Section 17.4, "MySQL Cluster
Programs". When data is stored by the storage engine, the tables (and table data) are stored in
NDB
the data nodes. Such tables are directly accessible from all other MySQL servers (SQL nodes) in the
cluster. Thus, in a payroll application storing data in a cluster, if one application updates the salary of
an employee, all other MySQL servers that query this data can see this change immediately.
However, a MySQL server that is not connected to a MySQL Cluster cannot use the storage
NDB
engine and cannot access any MySQL Cluster data.
The data stored in the data nodes for MySQL Cluster can be mirrored; the cluster can handle failures
of individual data nodes with no other impact than that a small number of transactions are aborted due
to losing the transaction state. Because transactional applications are expected to handle transaction
failure, this should not be a source of problems.
Individual nodes can be stopped and restarted, and can then rejoin the system (cluster). Rolling
restarts (in which all nodes are restarted in turn) are used in making configuration changes and
software upgrades (see Section 17.5.5, "Performing a Rolling Restart of a MySQL Cluster"). For more
information about data nodes, how they are organized in a MySQL Cluster, and how they handle and
store MySQL Cluster data, see Section 17.1.2, "MySQL Cluster Nodes, Node Groups, Replicas, and
Partitions".
Backing up and restoring MySQL Cluster databases can be done using the NDB native functionality
found in the MySQL Cluster management client and the program included in the
ndb_restore
MySQL Cluster distribution. For more information, see Section 17.5.3, "Online Backup of MySQL
Cluster", and Section 17.4.14, "ndb_restore — Restore a MySQL Cluster Backup". You can also use
the standard MySQL functionality provided for this purpose in and the MySQL server. See
mysqldump
Section 4.5.4, "mysqldump — A Database Backup Program", for more information.
MySQL Cluster nodes can use a number of different transport mechanisms for inter-node
communications, including TCP/IP using standard 100 Mbps or faster Ethernet hardware. It is also
possible to use the high-speed Scalable Coherent Interface (SCI) protocol with MySQL Cluster,
although this is not required to use MySQL Cluster. SCI requires special hardware and software; see
Section 17.3.5, "Using High-Speed Interconnects with MySQL Cluster", for more about SCI and using it
with MySQL Cluster.
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