Mysql Cluster Nodes, Node Groups, Replicas, And Partitions - Oracle 5.0 Reference Manual

• Global Checkpoint (GCP).
are synchronized and the redo-log is flushed to disk.

17.1.2. MySQL Cluster Nodes, Node Groups, Replicas, and Partitions

This section discusses the manner in which MySQL Cluster divides and duplicates data for storage.
Central to an understanding of this topic are the following concepts, listed here with brief definitions:
• (Data) Node.
below) assigned to the node group of which the node is a member.
Each data node should be located on a separate computer. While it is also possible to host multiple
processes on a single computer, such a configuration is not supported.
ndbd
It is common for the terms "node" and "data node" to be used interchangeably when referring to
an process; where mentioned, management (MGM) nodes
ndbd
nodes (mysqld
• Node Group.
replicas (see next item).
The number of node groups in a MySQL Cluster is not directly configurable; it is function of the
number of data nodes and of the number of replicas
shown here:
[number_of_node_groups] =
Thus, a MySQL Cluster with 4 data nodes has 4 node groups if
config.ini
is set to 4. Replicas are discussed later in this section; for more information about NoOfReplicas,
see Section 17.3.2.5, "Defining MySQL Cluster Data
• Partition.
as nodes participating in the cluster. Each node is responsible for keeping at least one copy of any
partitions assigned to it (that is, at least one replica) available to the cluster.
A replica belongs entirely to a single node; a node can (and usually does) store several replicas.
• Replica.
sometimes known as a partition replica. The number of replicas is equal to the number of nodes per
node group.
The following diagram illustrates a MySQL Cluster with four data nodes, arranged in two node groups
of two nodes each; nodes 1 and 2 belong to node group 0, and nodes 3 and 4 belong to node group
1. Note that only data (ndbd) nodes are shown here; although a working cluster requires an
process for cluster management and at least one SQL node to access the data stored by the cluster,
these have been omitted in the figure for clarity.
MySQL Cluster Nodes, Node Groups, Replicas, and Partitions
A GCP occurs every few seconds, when transactions for all nodes
An process, which stores a replica —that is, a copy of the partition (see
ndbd
processes) are specified as such in this discussion.
A node group consists of one or more nodes, and stores partitions, or sets of
number_of_data_nodes
file, 2 node groups if
Note
All node groups in a MySQL Cluster must have the same number of data
nodes.
This is a portion of the data stored by the cluster. There are as many cluster partitions
This is a copy of a cluster partition. Each node in a node group stores a replica. Also
(NoOfReplicas
/ NoOfReplicas
is set to 2, and 1 node group if
NoOfReplicas
Nodes".
1518
(ndb_mgmd processes) and SQL
configuration parameter), as
is set to 1 in the
NoOfReplicas
NoOfReplicas
ndb_mgm