Redo log — As we know, a logging mechanism of database changes.
Dumping a redo log:
Dumping a redo log is useful in cases of block corruption, either datafile corruption or log file corruption.
Its crucial information and also help full to retrieve the changes made in at the time.
Command: ALTER SYSTEM DUMP LOGFILE ‘FILE_NAME’;
Full command:
ALTER SYSTEM DUMP LOGFILE ‘FileName’
SCN MIN MinimumSCN
SCN MAX MaximumSCN
TIME MIN MinimumTime
TIME MAX MaximumTime
LAYER Layer
OPCODE Opcode
DBA MIN FileNumber . BlockNumber
DBA MAX FileNumber . BlockNumber
RBA MIN LogFileSequenceNumber . BlockNumber
RBA MAX LogFileSequenceNumber . BlockNumber;
Analyzing the dump:
Dump information starts from Redo log header, it contains DB ID, File size, Current SCN, start SCN etc..
After the header information, here comes the actual part.
It contains Redo change vectors, like INSERT/DELETE/UPDATE.
The file shows before image and after image as well.
Each change vector in the log file shows the type of the block,
type of operation, Obj#, scn, and many more.
For Eg:
CHANGE #1 TYP:0 CLS: 1 AFN:4 DBA:0x01001d38 OBJ:53102 SCN:0x0000.00197e86 SEQ:193 OP:10.14
index redo (kdxima): restored block before image, count=2
trans layer b.i.
KTB Redo
op: 0x05 ver: 0x01
op: R itc: 2
kdxima — Index redo, like that you will have a hint to show the kind of operation.
OP — opcode based on this we will know what kind of operation.
You can get all the information required to analyze the block corruptions
and redo corruptions.