This discussion is archived
8 Replies Latest reply: Aug 13, 2013 10:28 AM by KenTheTrog RSS

RMAN file order

KenTheTrog Newbie
Currently Being Moderated

In what order does rman backup and recover datafiles?

 

Is it by # of changes with the system ts df last?

 

Thanks!

-Ken

  • 1. Re: RMAN file order
    sb92075 Guru
    Currently Being Moderated

    KenTheTrog wrote:

     

    In what order does rman backup and recover datafiles?

     

    Is it by # of changes with the system ts df last?

     

    Thanks!

    -Ken

    Please explain  why the answer matters.

    How will you act differently after learning this minutiae?

  • 2. Re: RMAN file order
    Arun# Explorer
    Currently Being Moderated

    Use the following Query to find out yourself :-

     

    SELECT FILE#, INCREMENTAL_LEVEL, COMPLETION_TIME, BLOCKS, DATAFILE_BLOCKS

      FROM V$BACKUP_DATAFILE

      WHERE INCREMENTAL_LEVEL > 0

      ORDER BY COMPLETION_TIME;

  • 3. Re: RMAN file order
    KenTheTrog Newbie
    Currently Being Moderated

    Fair question, but if you don't know the answer, please refrain from replying.

     

    I'm monitoring a very large recovery and I'd just like to know.

  • 4. Re: RMAN file order
    KenTheTrog Newbie
    Currently Being Moderated

    Thanks for the SQL Arun, there doesn't seem to be an obvious pattern.

     

         FILE# INCREMENTAL_LEVEL COMPLETIO     BLOCKS DATAFILE_BLOCKS

    ---------- ----------------- --------- ---------- ---------------

            66                 0 10-AUG-13     164359          262144

            78                 0 10-AUG-13     392713          393216

            79                 0 10-AUG-13     301127          393216

            72                 0 10-AUG-13     129725          262144

            26                 0 10-AUG-13         89          131072

            58                 0 10-AUG-13         33          131072

            60                 0 10-AUG-13     257427          265344

            59                 0 10-AUG-13         58          131072

            71                 0 10-AUG-13     176978          262144

            81                 0 10-AUG-13         33          131072

            82                 0 10-AUG-13         45          131072

            85                 0 10-AUG-13         33          131072

            86                 0 10-AUG-13         45          131072

            87                 0 10-AUG-13         33          131072

            76                 0 10-AUG-13     162095          262144

     

    There must be some method for the way datafiles are queued up for channels.  Seems to me the restore just reverses the order since it just reads them back in from the backup pieces as they were layed out.

  • 5. Re: RMAN file order
    Arun# Explorer
    Currently Being Moderated

    Welcome Ken,

     

    As far as I know, RMAN allocate channels in numerical order. Read this document to get a clear picture.

     

    Regds,

     

    Arun

  • 6. Re: RMAN file order
    JohnWatson Guru
    Currently Being Moderated

    KenTheTrog wrote:

     

    In what order does rman backup and recover datafiles?

     

    As far I can remember, if you specify fileperset=1 the files are backed up in order of size descending. If you have filesperset > 1 it becomes more complicated as RMAN attempts to combine files of similar size in each backupset. Remember that files in a set are interleaved, so in effect backed up concurrently.

  • 7. Re: RMAN file order
    Alvaro Pro
    Currently Being Moderated

    For recovery purposes it also depends on how many channels you configured.

  • 8. Re: RMAN file order
    KenTheTrog Newbie
    Currently Being Moderated

    Question:

    Assuming a single channel and filesperset=1, what order does RMAN choose to backup datafiles?


    Answer:

    The order of files is random. The File Names are read from V$DATAFILE view and due to performance bug, the ORDER BY FILE# clause is removed, hence the query can return file# in random order.


Legend

  • Correct Answers - 10 points
  • Helpful Answers - 5 points