Using Key Ranges with an NDB › NDB Key Structure

NDB Key Structure

The VSAM key in an NDB is divided into the following parts:

• A type prefix, two bytes long
• For some records, a field code, two bytes long
• Key data, either the rest of the key, or four bytes shorter
• For some keys, a suffix, four bytes long

The following shows the key structures in ascending order:

• Control record (always first record in data set)

  Rectype: X'0000'

  Rest of key: All binary 0

• Transaction control record (always second record in data set)

  Rectype: X'0010'

  Rest of key: All binary 0

• Transaction journal records

  Rectype: X'0011'

  Sequence number: 2 bytes, binary (X'0001' to nnnn)

  Rest of key: All binary 0

• Field information records (2 types)
  • First (Basic Field Information):

    Rectype: X'0020'

    Field code: 2 bytes binary

    Rest of key: All binary 0

  • Second (Contains Key Statistics):

    Rectype: X'0021'

    Field code: 2 bytes binary

    Rest of key: All binary 0

• Key records

  Rectype: X'0030'

  Field code: 2 bytes binary

  Field value: (keylen - 8 bytes, see Storage of Values)

  Suffix: 4 bytes, binary

• RID to sequence key records (present only if NDB defined with a sequence key)

  Rectype: X'0032'

  RID: 4 bytes, binary

  Rest of key: All binary 0

• Data records. There are 2 formats, depending on whether the NDB has a sequence key, or not:
  • For databases defined without a sequence key, the format is:

    Rectype: x'0040'

    RID: 4 bytes, binary

    Reserved: (keylen - 10) bytes long

    Sequence number: 4 bytes binary (usually 0, used to handle large data records)

  • For databases defined with a sequence key, the format is:

    Rectype: x'0040'

    field code: 2 bytes, binary; always x'0001'

    Seq key value: (keylen - 8 bytes, see Storage of Values)

    Sequence number: 4 bytes binary (usually 0, used to handle large data records)