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  1. Derby
  2. DERBY-96

partial log record writes that occur because of out-of order writes need to be handled by recovery.



    • Improvement
    • Status: Closed
    • Major
    • Resolution: Fixed
    • Store
    • None


      Incomplete log record write that occurs because of
      an out of order partial writes gets recognized as complete during
      recovery if the first sector and last sector happens to get written.
      Current system recognizes incompletely written log records by checking
      the length of the record that is stored in the beginning and end.
      Format the log records are written to disk is:


      length LOG RECORD length


      This mechanism works fine if sectors are written in sequential manner or
      log record size is less than 2 sectors. I believe on SCSI types disks
      order is not necessarily sequential, SCSI disk drives may sometimes do a
      reordering of the sectors to optimize the performance. If a log record
      that spans multiple disk sectors is being written to SCISI type of
      devices, it is possible that first and last sector written before the
      crash; If this occurs recovery system will incorrectly interpret the
      log records was completely written and replay the record. This could
      lead to recovery errors or data corruption.

      This problem also will not occur if a disk drive has write cache with a
      battery backup which will make sure I/O request will complete.




            tsuresh Suresh Thalamati
            tsuresh Suresh Thalamati
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