8.3.2 Message Naming Conventions and Structure

This section describes the NDB Protocol message types and their structures.

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:

Operation TypeRequest (REQ)Response/Success (CONF)Response/Failure (REF)
Primary Key Lookup (TCKEY)TCKEYREQTCKEYCONFTCKEYREF
Unique Key Lookup (TCINDX)TCINDXREQTCINDXCONFTCINDXREF
Table or Index Scan (SCANTAB)SCANTABREQSCANTABCONFSCANTABREF
Result Retrieval (SCAN_NEXT)SCAN_NEXTREQSCANTABCONFSCANTABREF
Transaction Record Acquisition (TCSEIZE)TCSEIZEREQTCSEIZECONFTCSEIZEREF
Transaction Record Release (TCRELEASE)TCRELEASEREQTCRELEASECONFTCRELEASEREF

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).