3.2 NDB Protocol Messages

This section describes the NDB Protocol message types, their function, and their structure.

Naming Conventions.  Message names are constructed according to a simple pattern which should be readily apparent from the discussion of request and response types in the previous section. These are shown in the following matrix:

Table 3.1 NDB Protocol messages, with REQ, CONF, and REF message names

Operation Type	Request (REQ)	Response: Success (CONF)	Response: Failure (REF)
Primary Key Lookup (TCKEY)	TCKEYREQ	TCKEYCONF	TCKEYREF
Unique Key Lookup (TCINDX)	TCINDXREQ	TCINDXCONF	TCINDXREF
Table or Index Scan (SCANTAB)	SCANTABREQ	SCANTABCONF	SCANTABREF
Result Retrieval (SCAN_NEXT)	SCAN_NEXTREQ	SCANTABCONF	SCANTABREF
Transaction Record Acquisition (TCSEIZE)	TCSEIZEREQ	TCSEIZECONF	TCSEIZEREF
Transaction Record Release (TCRELEASE)	TCRELEASEREQ	TCRELEASECONF	TCRELEASEREF

CONF and REF are shorthand for “confirmed” and “refused”, respectively.

Three additional types of messages are used in some instances of inter-node communication. These message types are listed here:

1. A KEYINFO message contains information about the key used in a TCKEYREQ or TCINDXREQ message. It is employed when the key data does not fit within the request message. KEYINFO messages are also sent for index scan operations in which bounds are employed.

2. An ATTRINFO message contains nonkey attribute values which does not fit within a TCKEYREQ, TCINDXREQ, or SCANTABREQ message. It is used for:

   • Supplying attribute values for inserts and updates

   • Designating which attributes are to be read for read operations

   • Specifying optional values to read for delete operations

3. A TRANSID_AI message contains data returned from a read operation; in other words, it is a result set (or part of one).