Mysql Cluster Core Concepts - Oracle 5.0 Reference Manual

17.1.1. MySQL Cluster Core Concepts

NDBCLUSTER
persistence features.
The
NDBCLUSTER
options, but it is easiest to start with the storage engine at the cluster level. MySQL Cluster's
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.
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
Replicas, and
data nodes. One replica is sufficient for data storage, but provides no redundancy; therefore, it is
recommended to have 2 (or more) replicas to provide redundancy, and thus high availability. A data
node is started with the command
Node Daemon").
MySQL Cluster tables in MySQL 5.0 are stored completely in memory rather than on disk (this is
why we refer to MySQL cluster as an in-memory database). In MySQL 5.1, MySQL Cluster NDB 6.X,
and later, some MySQL Cluster data can be stored on disk, but we do not expect to backport this
functionality to MySQL 5.0; see
• SQL node: This is a node that accesses the cluster data. In the case of MySQL Cluster, an SQL
node is a traditional MySQL server that uses the
process started with the
mysqld
which are explained elsewhere in this chapter, possibly with additional MySQL server options as
well.
An SQL node is actually just a specialized type of API node, which designates any application which
accesses Cluster data. Another example of an API node is the
to restore a cluster backup. It is possible to write such applications using the NDB API. For basic
information about the NDB API, see
MySQL Cluster Core Concepts
(also known as NDB) is an in-memory storage engine offering high-availability and data-
storage engine can be configured with a range of failover and load-balancing
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.
However, MySQL 5.0 does not support the use of multiple data nodes on a
single computer in a production setting. See
Relating to Multiple MySQL Cluster
Partitions"). For example, with two replicas, each having two fragments, you need four
MySQL Cluster Disk Data
--ndbcluster
Important
It is not realistic to expect to employ a three-node setup in a production
environment. Such a configuration provides no redundancy; to benefit from
Nodes".
Section 17.1.2, "MySQL Cluster Nodes, Node Groups,
(see Section 17.4.1,
ndbd
NDBCLUSTER
[1610]
Getting Started with the NDB
1516
Section 17.1.5.9, "Limitations
"ndbd — The MySQL Cluster Data
Tables, for more information.
storage engine. An SQL node is a
and
--ndb-connectstring
utility that is used
ndb_restore
API.
NDB
options,