8.3.1 NDB Protocol Overview

MySQL Cluster data and API nodes communicate with one another by passing messages to one another. The sending of a message from one node and its reception by another node is referred to as a signal; the NDB Protocol is the set of rules governing the format of these messages and the manner in which they are passed.

An NDB message is typically either a request or a response. A request indicates that an API node wants to perform an operation involving cluster data (such as retrieval, insertion, updating, or deletion) or transactions (commit, roll back, or to fetch or relase a transaction record). A request is, when necessary, accompanied by key or index information. The response sent by a data node to this request indicates whether or not the request succeeded and, where appropriate, is accompanied by one or more data messages.

Request types.  A request is represented as a REQ message. Requests can be divided into those handling data and those handling transactions:

Response types.  A response indicates either the success or the failure of the request to which it is sent in reply:

For more information about these message types and their relationship to one another, see Section 8.3.2, “NDB Protocol Messages”.