Regarding Controlfile.......

Question

Below is Oracle Documentation from Physical Storage Structures
The control file contains the following types of records:
Circular reuse recordsThese records contain noncritical information that is eligible to be overwritten if needed. When all available record slots are full, the database either expands the control file to make room for a new record or overwrites the oldest record. Examples include records about archived redo log files and RMAN backups.
Question:
How to find out the circular reuse records from view v$controlfile_record_section?

Answer 1

TSharma wrote:
You can generate a controlfile dump with the higher dump level. The higher he dump level  more circular reuse records you will see at the end of the dump file.
For example:
Alter session set events 'immediate trace name controlf level 3';
Alter session set events 'immediate trace name controlf level 4';
Alter session set events 'immediate trace name controlf level 15';
Interesting point about levels up to 15.
Level 10 actually gives you a raw dump of the file - so there's a funny jump from 9 to 11 which I hadn't noticed.
The OP won't get any extra information from the dumps that isn't available in the v$controlfile_record_section, though - since any section which hasn't used any records won't give a clue about whether or not it would recycle:
Extract from the view:
TYPE                         RECORD_SIZE RECORDS_TOTAL RECORDS_USED FIRST_INDEX LAST_INDEX LAST_RECID
LOG HISTORY                           56         10888        10888        2545       2544     157246
OFFLINE RANGE                        200          1021            0           0          0          0
ARCHIVED LOG                         584         21480        21480        3203       3202      67642
BACKUP SET                            40         32672        32672       15883      15882     717917
BACKUP PIECE                         736         32128        32128        2155       2154     727763
BACKUP DATAFILE                      200         29288        29288       22862      22861     836798
BACKUP REDOLOG                        76         21488        21488         146        145     146154
DATAFILE COPY                        736         63936        63936       52286      52285     468871
BACKUP CORRUPTION                     44          1113            0           0          0          0
COPY CORRUPTION                       40          1021            0           0          0          0
DELETED OBJECT                        20        418048       418048      116058     116057    2210380
PROXY COPY                           928          1006            0           0          0          0
BACKUP SPFILE                        124          1812         1812        1438       1437      23634
It's a fairly safe bet that the sections where FIRST_INDEX is greater than LAST_INDEX are sections where a limited size array is being reused. But what can you deduce about OFFLINE RANGE ?
Comparing this with the dump, the circular ranges which have been used show things like:
LOG FILE HISTORY RECORDS
(size = 56, compat size = 56, section max = 292, section in-use = 292,
  last-recid= 311, old-recno = 20, last-recno = 19)
(extent = 1, blkno = 95, numrecs = 292)
Earliest record:
RECID #20 Recno 20 Record timestamp  01/23/12 09:22:58 Thread=1 Seq#=20 Link-Recid=19 kccic-Recid=1
  Low scn: 0x0000.0009914b 01/23/12 09:22:45 Next scn: 0x0000.00099d0d
Latest record:
RECID #311 Recno 19 Record timestamp  06/24/13 08:00:24 Thread=1 Seq#=311 Link-Recid=310 kccic-Recid=1
  Low scn: 0x0b86.404a1635 06/14/13 16:06:45 Next scn: 0x0b86.404a8554
(Different control file, by the way).
Again this doesn't show us anything about the circular reuse ranges if they haven't bee used.
Regards
Jonathan Lewis