MySQL Cluster Tutorial - cdn.oreillystatic.com

• The management node(s) can continue to act as arbitrators (avoiding a split-brain
scenario). For this reason, it is still important to run those processes on separate hosts
from the data nodes;
• Some reporting information (for example, memory usage) is not yet available in the
Cluster Manager and can still be performed using the ndb_mgm tool.
When using MySQL Cluster Manager, the 'angel' processes are no longer needed (or
created) for the data nodes, as it becomes the responsibility of the agents to detect the
failure of the data nodes and recreate them as required. Additionally, the agents extend
this functionality to include the management nodes and MySQL Server nodes.
It should be noted that there is no angel process for the agents themselves and so for the
highest levels of availability, the administrator may choose to use a process monitor to
detect the failure of an agent and automatically restart it. When an agent is unavailable,
the MySQL Cluster database continues to operate in a fault-tolerant manner but
management changes cannot be made until it is restarted. When the agent process is
restarted, it re-establishes communication with the other agents and has access to all
current configuration data, ensuring that the management function is restored.
When using MySQL Cluster Manager, the 'angel' processes are no longer needed (or
created) for the data nodes, as it becomes the responsibility of the agents to detect the
failure of the data nodes and recreate them as required. Additionally, the agents extend
this functionality to include the management nodes and MySQL Server nodes.
It should be noted that there is no angel process for the agents themselves and so for the
highest levels of availability, the administrator may choose to use a process monitor to
detect the failure of an agent and automatically restart it. When an agent is unavailable,
the MySQL Cluster database continues to operate in a fault-tolerant manner but
management changes cannot be made until it is restarted. When the agent process is
restarted, it re-establishes communication with the other agents and has access to all
current configuration data, ensuring that the management function is restored.
MySQL Cluster Manager Model & Terms
Before looking at how to install, configure and use MySQL Cluster Manager, it helps to
understand a number of components and the relationships between them (as viewed by
the MySQL Cluster Manager). Figure 3 illustrates a number of these entities and then there
is a brief description of each.
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