SQL Server 2008记录头第一个字节各部分含义

• Byte 0 is the TagA byte of the record metadata.
  • Bit 4 means the record has a NULL bitmap and bit 5 means the record has variable length columns. If 0x40 (bit 6) was also set, that would indicate that the record has a versioning tag. If 0x80 (bit 7) was also set, that would indicate that byte 1 has a value in it.

  • Bits 1-3 of byte 0 give the record type. The possible values are:
    • 0 = primary record. A data record in a heap that hasn't been forwarded or a data record at the leaf level of a clustered index.

    • 1 = forwarded record

    • 2 = forwarding record

    • 3 = index record

    • 4 = blob fragment

    • 5 = ghost index record

    • 6 = ghost data record

    • 7 = ghost version record. A special 15-byte record containing a single byte record header plus a 14-byte versioning tag that is used in some circumstances (like ghosting a versioned blob record)

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