=====Overview=====
In order to fix that, we have to:

  - Mount the database (if it is down, although shouldn't be)
  - Clear the logfile groups
  - Open the database normally

====Mount====
Now, firstly, to mount the database we have to have: 

  * Parameter file(pfile or SPFILE)
  * Control file (Binary, NOT SQL commands)

If we have these two files, we can mount ANY database regardless if we have or don't have: datafiles, redo log files or whatever. S

<sxh bash>
SQL> startup mount;
ORACLE instance started.

Total System Global Area 1.0689E+10 bytes
Fixed Size                  2237776 bytes
Variable Size            8220838576 bytes
Database Buffers         2449473536 bytes
Redo Buffers               16924672 bytes
Database mounted.
</sxh>

====Clear log files====
Once we have the database mounted, we can check if all the files are correct and the header isn't corrupted:


<sxh bash>
NAME                                                         STATUS   FILE# CONTROL_FILE_SCN     DATAFILE_SCN DATAFILE_STATUS
------------------------------------------------------------ -------- ----- ---------------- ---------------- ----------------
/dbLFALP/system01.dbf                                        SYSTEM       1   14894573171135   14894573171135 Startup   Normal
/dbLFALP/sysaux01.dbf                                        ONLINE       2   14894573171135   14894573171135 Startup   Normal
/dbLFALP/tb_crew_large-02.dbf                                ONLINE       3   14894573171135   14894573171135 Startup   Normal
/dbLFALP/users01.dbf                                         ONLINE       4   14894573171135   14894573171135 Startup   Normal
/dbLFALP/ix_crew_large-01.dbf                                ONLINE       5   14894573171135   14894573171135 Startup   Normal
/dbLFALP/ix_crew_medium-01.dbf                               ONLINE       6   14894573171135   14894573171135 Startup   Normal
/dbLFALP/ix_crew_small-01.dbf                                ONLINE       7   14894573171135   14894573171135 Startup   Normal
/dbLFALP/ix_crl_large-01.dbf                                 ONLINE       8   14894573171135   14894573171135 Startup   Normal
/dbLFALP/ix_crl_medium-01.dbf                                ONLINE       9   14894573171135   14894573171135 Startup   Normal
/dbLFALP/ix_crl_small-01.dbf                                 ONLINE      10   14894573171135   14894573171135 Startup   Normal
/dbLFALP/ix_mpp_large-01.dbf                                 ONLINE      11   14894573171135   14894573171135 Startup   Normal

NAME                                                         STATUS   FILE# CONTROL_FILE_SCN     DATAFILE_SCN DATAFILE_STATUS
------------------------------------------------------------ -------- ----- ---------------- ---------------- ----------------
/dbLFALP/ix_mpp_medium-01.dbf                                ONLINE      12   14894573171135   14894573171135 Startup   Normal
/dbLFALP/ix_mpp_small-01.dbf                                 ONLINE      13   14894573171135   14894573171135 Startup   Normal
/dbLFALP/ix_ops_large-01.dbf                                 ONLINE      14   14894573171135   14894573171135 Startup   Normal
/dbLFALP/ix_ops_medium-01.dbf                                ONLINE      15   14894573171135   14894573171135 Startup   Normal
/dbLFALP/i00-01.dbf                                          ONLINE      16   14894573171135   14894573171135 Startup   Normal
/dbLFALP/tb_base-01.dbf                                      ONLINE      17   14894573171135   14894573171135 Startup   Normal
/dbLFALP/tb_crew_large-01.dbf                                ONLINE      18   14894573171135   14894573171135 Startup   Normal
/dbLFALP/tb_crew_medium-01.dbf                               ONLINE      19   14894573171135   14894573171135 Startup   Normal
/dbLFALP/tb_crew_small-01.dbf                                ONLINE      20   14894573171135   14894573171135 Startup   Normal
/dbLFALP/tb_crl_large-01.dbf                                 ONLINE      21   14894573171135   14894573171135 Startup   Normal
/dbLFALP/tb_crl_medium-01.dbf                                ONLINE      22   14894573171135   14894573171135 Startup   Normal

NAME                                                         STATUS   FILE# CONTROL_FILE_SCN     DATAFILE_SCN DATAFILE_STATUS
------------------------------------------------------------ -------- ----- ---------------- ---------------- ----------------
/dbLFALP/tb_crl_small-01.dbf                                 ONLINE      23   14894573171135   14894573171135 Startup   Normal
/dbLFALP/tb_mpp_large-01.dbf                                 ONLINE      24   14894573171135   14894573171135 Startup   Normal
/dbLFALP/tb_mpp_medium-01.dbf                                ONLINE      25   14894573171135   14894573171135 Startup   Normal
/dbLFALP/tb_mpp_small-01.dbf                                 ONLINE      26   14894573171135   14894573171135 Startup   Normal
/dbLFALP/tb_ops_large-01.dbf                                 ONLINE      27   14894573171135   14894573171135 Startup   Normal
/dbLFALP/tb_ops_medium-01.dbf                                ONLINE      28   14894573171135   14894573171135 Startup   Normal
/dbLFALP/tb_ops_small-01.dbf                                 ONLINE      29   14894573171135   14894573171135 Startup   Normal
/dbLFALP/tools-01.dbf                                        ONLINE      30   14894573171135   14894573171135 Startup   Normal
/dbLFALP/t00-01.dbf                                          ONLINE      31   14894573171135   14894573171135 Startup   Normal
/dbLFALP/ix_ops_small-01.dbf                                 ONLINE      32   14894573171135   14894573171135 Startup   Normal
/dbLFALP/undo_01.dbf                                         ONLINE      33   14894573171135   14894573171135 Startup   Normal
</sxh>


So once they have been fixed, we can proceed with the clearing:



<sxh bash>
SQL> alter database clear logfile group 1;

Database altered.

SQL> alter database clear logfile group 3;

Database altered.

SQL> alter database open;

Database altered.

</sxh>

Monitor the alert log, just to be sure that all is fine. Once the database opens, please switch couple times to guarantee consistency and that all mechanisms are working.

<sxh bash>

SQL> alter system switch logfile;

System altered.

SQL> /

System altered.

SQL> /

System altered.
</sxh>