2.3.15 The Ndb_cluster_connection Class

2.3.15.1 Ndb_cluster_connection Methods

Abstract

This class represents a connection to a cluster of data nodes.

Parent class.  None

Child classes.  None

Description.  An NDB application program should begin with the creation of a single Ndb_cluster_connection object, and typically makes use of a single Ndb_cluster_connection. The application connects to a cluster management server when this object's connect() method is called. By using the wait_until_ready() method it is possible to wait for the connection to reach one or more data nodes.

Application-level partitioning.  There is no restriction against instantiating multiple Ndb_cluster_connection objects representing connections to different management servers in a single application, nor against using these for creating multiple instances of the Ndb class. Such Ndb_cluster_connection objects (and the Ndb instances based on them) are not required even to connect to the same cluster.

For example, it is entirely possible to perform application-level partitioning of data in such a manner that data meeting one set of criteria are handed off to one cluster using an Ndb object that makes use of an Ndb_cluster_connection object representing a connection to that cluster, while data not meeting those criteria (or perhaps a different set of criteria) can be sent to a different cluster through a different instance of Ndb that makes use of an Ndb_cluster_connection pointing to the second cluster.

It is possible to extend this scenario to develop a single application that accesses an arbitrary number of clusters. However, in doing so, the following conditions and requirements must be kept in mind:

Therefore, it is imperative in designing and implementing any application that accesses multiple clusters in a single session, that a separate set of Ndb_cluster_connection and Ndb objects be instantiated for connecting to each cluster management server, and that no confusion arises as to which of these is used to access which MySQL Cluster.

It is also important to keep in mind that no direct sharing of data or data nodes between different clusters is possible. A data node can belong to one and only one cluster, and any movement of data between clusters must be accomplished on the application level.

For examples demonstrating how connections to two different clusters can be made and used in a single application, see Section 2.4.2, “Using Synchronous Transactions and Multiple Clusters”, and Section 3.5.2, “MGM API Event Handling with Multiple Clusters”.

Methods.  The following table lists the public methods of this class and the purpose or use of each method:

MethodPurpose / Use
Ndb_cluster_connection()Constructor; creates a connection to a cluster of data nodes.
connect()Connects to a cluster management server.
get_auto_reconnect()

Gets the auto-reconnection setting for API nodes using this Ndb_cluster_connection.

get_latest_error()

Whether or not the most recent attempt to connect succeeded.

get_latest_error_msg()

If the most recent attempt to connect failed, provides the reason.

get_next_ndb_object()

Used to iterate through multiple Ndb objects.

lock_ndb_objects()

Disables the creation of new Ndb objects.

set_auto_reconnect()

Enables or disables auto-reconnection of API nodes using this Ndb_cluster_connection.

set_name()Provides a name for the connection
set_optimized_node_selection()Used to control node-selection behavior.
set_timeout()Sets a connection timeout
unlock_ndb_objects()

Enables the creation of new Ndb objects.

wait_until_ready()Waits until a connection with one or more data nodes is successful.

For detailed descriptions, signatures, and examples of use for each of these methods, see Section 2.3.15.1, “Ndb_cluster_connection Methods”.

Class diagram.  This diagram shows all the available methods of the Ndb_cluster_connection class:

Public methods of the Ndb_cluster_connection class.