Parnassusdata Software Database Recovery Team

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HOW TO RECOVER A DATABASE HAVING ADDED A DATAFILE SINCE THE LAST BACKUP
-----------------------------------------------------------------------

This bulletin outlines the steps required in performing database recovery
having added a datafile to the database since the last backup was taken. 
Section A is applicable to Oracle release 7.x. Section B applies only to
Oracle releases 7.3.x and above.

PLEASE READ THROUGH ALL STEPS AND WARNINGS BEFORE ATTEMPTING TO USE THIS
BULLETIN.


A. Current controlfile, backup of datafile exists (Oracle release 7.x)
   ===================================================================

 A valid (either hot or cold) backup of the datafiles exists, except for the
 datafile created since the backup was taken. The current controlfile exists. 
 The database is in archivelog mode (see note (c) at bottom of page).

 1. Restore ONLY the datafiles (those that have been lost or damaged) from the 
    last hot or cold backup. The current online redo logs and control file(s) 
    must be intact.

 2. Mount the database

 3. Create a new datafile using the 'ALTER DATABASE CREATE DATAFILE' command.

    a. The datafile can be created with the same name as the original
       file. For example,

       SQLDBA> alter database create datafile
            2> '/dev1/oracle/dbs/testtbs.dbf';
       Statement processed.
 
    b. The datafile can be created with a different filename to the original. 
       This option might be chosen if the original file was lost due to disk 
       failure and the failed disk was still unavailable; the new file would 
       then be created on a different device. For example,

       SQLDBA> alter database create datafile
            2> '/dev1/oracle/dbs/testtbs.dbf'
            3> as
            4> '/dev2/oracle/dbs/testtbs.dbf';
       Statement processed.

       The above command creates a new datafile on the dev2 device. The file
       is created using information, stored in the control file, from the 
       original file. The command implicitly renames the filename in the 
       control file.
   
       NOTE: IT IS VERY IMPORTANT TO SPECIFY THE CORRECT FILENAME WHEN
             RECREATING THE LOST DATAFILE. IF YOU SPECIFY AN EXISTING
             ORACLE DATAFILE, THAT DATAFILE WILL BE INITIALISED AND WILL
             ITSELF REQUIRE RECOVERY.

 4. Recover the database.

    SQLDBA> recover database
    ORA-00279: Change 6677 generated at 06/03/97 15:20:24 needed for thread 1
    ORA-00289: Suggestion : /dev1/oracle/dbs/arch/arch000074.arc
    ORA-00280: Change 6677 for thread 1 is in sequence #74
    Specify log: {<RET>=suggested | filename | AUTO | CANCEL}
    
    At this point the recovery procedure will wait for the user to supply the
    information requested regarding the name and location of the archived log
    files. For example, entering AUTO directs Oracle to apply the suggested 
    redo log and any others that it requires to recover the datafiles.

    Applying suggested logfile...
    Log applied.
              :
              :
    <Application of further redo logs>
              :
              :
    Media recovery complete.

 5. Open the database

    SQLDBA> alter database open;
    Statement processed.



B. Old controlfile, no backup of datafile (Oracle release 7.3.x and above)
   =======================================================================

 A valid (either hot or cold) backup of the datafiles exists, except for the
 datafile created since the backup was taken. The controlfile is a backup from
 before the creation of the new datafile. The database is in archivelog mode 
 (see note (c) at bottom of page).

 NOTE : 'svrmgrl' has been replaced by SQL*Plus starting from Oracle8i
        So the 'SVRMGR>' prompt is than replaced by 'SQL>'

 1. Restore the datafiles (those that have been lost or damaged) from the 
    last hot or cold backup. Also restore the old copy of the controlfile.
    The current online redo logs must be intact.

 2. Mount the database

 3. Start media recovery, specifying backup controlfile

    SVRMGR> recover database using backup controlfile
    ORA-00279: Change 6677 generated at 06/03/97 15:20:24 needed for thread 1
    ORA-00289: Suggestion : /dev1/oracle/dbs/arch/arch000074.arc
    ORA-00280: Change 6677 for thread 1 is in sequence #74
    Specify log: {<RET>=suggested | filename | AUTO | CANCEL}

    At this point, apply the archived logs as requested. Eventually Oracle
    will encounter redo to be applied to the non-existent datafile. The 
    recovery session will exit with the following message, and will return
    the user to the Server Manager prompt:

    ORA-00283: Recovery session canceled due to errors
    ORA-01244: unnamed datafile(s) added to controlfile by media recovery
    ORA-01110: data file 5: '/dev1/oracle/dbs/testtbs.dbf'
 
 4. Recreate the missing datafile. To do this, select the relevant filename 
    from v$datafile:

    SVRMGR> select name from v$datafile where file#=5;
    NAME
    -------------------------------------------------------
    UNNAMED0005

    Now recreate the file:

    SVRMGR> alter database create datafile
         2> 'UNNAMED0005'
         3> as
         4> '/dev1/oracle/dbs/testtbs.dbf';



 5. Restart recovery

    SVRMGR> recover database using backup controlfile
    ORA-00279: Change 6747 generated at 09/24/97 16:57:18 needed for thread 1
    ORA-00289: Suggestion : /dev1/oracle/dbs/arch/arch000079.arc
    ORA-00280: Change 6747 for thread 1 is in sequence #79
    Specify log: {<RET>=suggested | filename | AUTO | CANCEL}

    Apply archived logs as requested. Prior to Oracle8, recovery must apply
    the complete log which was current at the time of the datafile creation
    (in the above example, this would be log sequence 79). A recovery to a
    point in time before the end of this log would result in errors:

    ORA-01196: file 1 is inconsistent due to a failed media recovery session
    ORA-01110: data file 1: '/dev1/oracle/dbs/systbs.dbf'

    If this happens, re-recover the database and ensure that the complete log
    is applied (plus any further redo if required). This limitation does
    not exist from Oracle 8.0+.

    Eventually, Oracle will request the archived log corresponding to the 
    current online log. It does this because the (backup) controlfile has no 
    knowledge of the current log sequence. If an attempt is made to apply the 
    suggested log, the recovery session will exit with the following message:

    ORA-00308: cannot open archived log '/dev1/oracle/dbs/arch/arch000084.arc'
    ORA-07360: sfifi: stat error, unable to obtain information about file.
    SVR4 Error: 2: No such file or directory

    At this stage, simply restart the recovery session and apply the current
    online log. The best way to do this is to try applying the online redo 
    logs one by one until Oracle completes media recovery:

    SVRMGR> recover database using backup controlfile
    ORA-00279: Change 6763 generated at 09/24/97 16:57:59 needed for thread 1
    ORA-00289: Suggestion : /dev1/oracle/dbs/arch/arch000084.arc
    ORA-00280: Change 6763 for thread 1 is in sequence #84
    Specify log: {<RET>=suggested | filename | AUTO | CANCEL}
    /dev1/oracle/dbs/log2.dbf
    Log applied.
    Media recovery complete.

 6. Open the database

    SVRMGR> alter database open resetlogs;

    The resetlogs option must be chosen to resynchronize the controlfile. 

    
NOTES:
======

a) These techniques can be used whether the database was closed either 
   cleanly or uncleanly (aborted).

b) If the database is recovered using an incomplete recovery technique (either
   time-based, cancel-based, or change-based), and is recovered to a point in
   time before the datafile was originally created, any references to that
   datafile will be removed from the database when the database is opened.

   Oracle handles this situation as follows:

   - The 'alter database create datafile....' command creates a reference in 
     the controlfile for the datafile.
   - Incomplete recovery terminates before applying redo that would create a
     corresponding row for the datafile in the file$ dictionary table.
   - When the database is opened, Oracle detects an inconsistency between file$
     and the controlfile and resolves in favour of file$, deleting the entry
     from the controlfile. 

c) It may be possible to recover the datafile using this technique even if the
   database is not in archivelog mode. However, this relies on the required 
   redo being available in the online redo logs.