MySQL Cluster Core Concepts

NDBCLUSTER
(also known as NDB
) is an in-memory
storage engine offering high-availability and data-persistence
features.

The NDBCLUSTER
storage engine can be
configured with a range of failover and load-balancing options,
but it is easiest to start with the storage engine at the cluster
level. MySQL Cluster's NDB
storage
engine contains a complete set of data, dependent only on other
data within the cluster itself.

The “Cluster
” portion of MySQL Cluster is configured
independently of the MySQL servers. In a MySQL Cluster, each part
of the cluster is considered to be a node
.

Note
In many contexts, the term “node
” is used to
indicate a computer, but when discussing MySQL Cluster it means
a process
. It is possible to run multiple
nodes on a single computer; for a computer on which one or more
cluster nodes are being run we use the term cluster
host
.

There are three types of cluster nodes, and in a minimal MySQL
Cluster configuration, there will be at least three nodes, one of
each of these types:

Management node
(MGM node): The role of
this type of node is to manage the other nodes within the
MySQL Cluster, performing such functions as providing
configuration data, starting and stopping nodes, running
backup, and so forth. Because this node type manages the
configuration of the other nodes, a node of this type should
be started first, before any other node. An MGM node is
started with the command ndb_mgmd
.

Data node
: This type of node stores
cluster data. There are as many data nodes as there are
replicas, times the number of fragments (see
Section 1.2, “MySQL Cluster Nodes, Nod