Log Records

Its fields are

• LSN : It is the address of the first byte of the log record. It is a monotonically increasing value.
• Type : It indicates whether this is a
  • compensation record
  • regular update record
  • commit protocol-related record or
  • nontransaction-related record
• TransID : It identifies the transaction.
• PrevLSN : It is the LSN of the preceding log record written by the same transaction.
• PageID : Present only in records of type 'update' or 'compensate'. It identifies the page to which the updates of this record were applied. It consists of an objectID and a page number within that object. ARIES can deal with a log record that contains updates for multiple pages.
• UndoNxtLSN : Present only in CLR's.It is the LSN of the next log record of this transaction that is to be processed during rollback.
• Data : This is the redo and/or undo data that describes the update that was performed. CLR's contain only redo information, since they are never undone.