1. Julian Dyke Independent Consultant
Redo Internals
Julian Dyke
Independent Consultant
Web Version
© 2005 Julian Dyke
juliandyke.com

2. Agenda What is Redo? Redo Records Change Vectors Row Operations
Index Operations
Other Redo Operations
Direct Loads / NOLOGGING
Transaction Auditing
Supplemental Logging

3. What is Redo?
Redo logs contain a history of all changes made to the database
Redo log files are used by
Recovery (instance and media)
Log Miner
Oracle Streams
Every change made to the database is
written to the redo log buffer before it is written to the data block buffer
written to the redo log file before it is written to the data file
The redo log buffer is flushed to the redo log file when a COMMIT is issued
For each change, the server process
pins data block buffer(s) in exclusive mode
builds change vectors in PGA
constructs redo record in PGA
determines space required in log buffer
allocates space in log buffer
changes data block(s) in buffer cache

4. What is Redo? Redo log files
Include all changes made by DML statements
INSERT
UPDATE
DELETE
SELECT FOR UPDATE
Do not include DML statement text
Include all changes made to dictionary objects by DDL statements
Include DDL statement text (9.0.1 and above)
Include all changes made by recursive statements

5. Buffers and Writers Redo Log Buffer Redo Log File LGWR
Data File
Data Block Buffer
DBWR

6. Logging and Archiving Redo Log Files Archive Log Files Arch 1 LGWR
Group 1
Group 3
Group 2
ARCH
Arch 2
Arch 5
Arch 4
Arch 3
Arch 6
Redo Log Files
Archive Log Files

7. ... Redo Log Files Redo log uses operating system block size
usually 512 bytes
format dependent on
operating system
Oracle version
Each redo log consists of
header
redo records
Redo log is written sequentially
...
Block 0
Block 1
Block 2
Redo Record 1
File Header
Redo Header
Block 3
Redo Records 2 & 3
Block 4
Redo Records 3 & 4
Block M
Redo Record N

8. ..... Redo Records A redo record consists of redo record header
one or more change vectors
Each redo record contains undo and redo for an atomic change
Some changes do not require undo
Redo Record Header
Change #1
Change #2
Change #3
Change #N
.....

9. Redo Record Header Every redo record has a header Fields include
REDO RECORD - Thread:1 RBA: 0x cf.0010 LEN: 0x019c VLD: 0x01 SCN: 0x eb1279 SUBSCN: 1 05/08/ :44:12
Fields include
Thread
Thread Number
RBA
Redo Byte Address
LEN
Length of record in bytes
SCN
System Change Number
Date and Time of Change

10. Redo Byte Address (RBA)
Every redo record has a Redo Byte Address (RBA) e.g.
RBA: 0x cf.0010
RBA is 10 bytes in length
RBA identifies start of redo record
Fields are
Log sequence number (0x3666)
Block number within redo log (0xcf)
Byte number within block (0x10)

11. System Change Number (SCN)
Also called System Commit Number
Defines committed version of database
SCN is 6 bytes in length
SCN:0x0000.0ac67cc3
Contains
Wrap (2 bytes) e.g 0000
Base (4 bytes) e.g 0ac67cc3
Base is incremented for each new SCN
Saved in redo record header
RAC databases maintain a global SCN
Distributed transactions use highest SCN

12. Change Vector Describes a change to a single data block Can apply to
undo headers
undo blocks
data segment headers
data blocks
Is created in PGA before the data block buffer is modified
Consists of
header
array of change record lengths
array of change records

13. Change Vector For example 10 20 48 2 29 28 16 Change Record 1
Length Vector
Change Header

14. Change Vector Header Every change vector has a header e.g.
CHANGE #2 TYP:0 CLS: 1 AFN:5 DBA:0x0144d023 SCN:0x0000.0ac67cce SEQ: 4 OP:11.5
Fields include
CHANGE
Change number
TYP
Change type
CLS
Class
AFN
Absolute File Number
DBA
Relative Database Block Address
SCN
System Change Number
SEQ
Sequence Number (relative to SCN) OP
Operation Code

15. Block Classes Class in change header is equivalent to X$BH.CLASS
Description 1
Data Block 2
Sort Block 3
Deferred Undo Segment Blocks 4
Segment Header Block (Table) 5
Deferred Undo Segment Header Blocks 6
Free List Blocks 7
Extent Map Blocks 8
Space Management Bitmap Blocks 9
Space Management Index Blocks 10
Unused
11 + 2r
Segment Header for Undo Segment r
12 + 2r
Data Blocks for Undo Segment r
e.g. 11 is System Rollback Segment Header

16. Database Block Address (DBA)
Every database block has a Database Block Address (DBA) e.g.
DBA:0x0144d023
DBA is 4 bytes in length
Fields are
Upper 10 bits represent relative file number
Lower 22 bits represent block number
For example
DECLARE l_dba NUMBER := TO_NUMBER ('0144D023','XXXXXXXX'); l_file NUMBER := DBMS_UTILITY.DATA_BLOCK_ADDRESS_FILE (l_dba); l_block NUMBER := DBMS_UTILITY.DATA_BLOCK_ADDRESS_BLOCK (l_dba); BEGIN DBMS_OUTPUT.PUT_LINE ('File : '||l_file); DBMS_OUTPUT.PUT_LINE ('Block : '||l_block); END;

17. Operation Codes
Each change is represented by an operation in the redo log
There are over 150 different operations
Each operation has an layer code and a sub code e.g. 11.2
Layers include
Layer
Description 4
Block Cleanout 5
Transaction Management 10
Index Operations 11
Row Operations 13
Segment Management 14
Extent Management 17
Tablespace Management
Layer
Description 18
Block Image (Hot backups) 19
Direct Loader 20
Compatibility Segment 22
Locally Managed Tablespaces 23
Block Writes 24
DDL Statements

18. Transactions
The first DML statement in a session creates a transaction
Allocates an undo segment
Creates a 5.2 change to update transaction table in undo segment header
CHANGE #1 TYP:0 CLS:25 AFN:3 DBA:0x00c0012e SCN:0x0000.0ac86eb8 SEQ: 1 OP:5.2 ktudh redo: slt: 0x0010 sqn: 0x a flg: 0x0012 siz: 96 fbi: uba: 0x00c04d20.234b.0e pxid: 0x
A commit (or rollback) ends the transaction
A 5.4 change is created for a commit
CHANGE #1 TYP:0 CLS:25 AFN:3 DBA:0x00c0012e SCN:0x0000.0ac86ebf SEQ: 1 OP:5.4 ktucm redo: slt: 0x0010 sqn: 0x a srt: 0 sta: 9 flg: 0x0
Rollbacks apply all undo for the transaction followed by a commit

19. Transaction ID (XID) Every transaction has an XID
xid: 0x e b
XID is 8 bytes in length
Contains
Undo segment number (USN) of transaction (0x0004)
Undo segment header transaction table slot (0x00e)
Sequence number (wrap) (0x b)

20. Undo Block Address (UBA)
Address of change in undo block
uba: 0x00c01f
UBA is 7 bytes in length
Contains
DBA of undo block (0x00c01f17)
Sequence number (2758)
Record number in block (4)

21. Transactions Statements Redo Logs Undo Header Undo Block Data Block
UPDATE t1 SET c2 = 101 WHERE c1 = 1;
SLOT
STATUS
Undo Header
5.2 10
Undo Slot 0 c2 = 100 9
Undo Slot 0 c2 = 100
5.1
Undo Block
Redo Slot 0 c2 = 101
11.5
Undo Slot 1 c2 = 200
UPDATE t1 SET c2 = 201 WHERE c1 = 2;
Undo Slot 1 c2 = 200
5.1
Redo Slot 1 c2 = 201
11.5
Data Block
SLOT C1 C2 1
100 2
200
COMMIT;
Commit
5.4
101
201

22. Physiological Logging
Oracle normally uses physiological logging
Only changes made to each block are recorded
Statement
Undo
Redo
INSERT INTO t1 VALUES (1, 'ABC');
Delete row 1
Row 1 c1 := 1 c2 := 'ABC'
UPDATE t1 SET c2 = 'DEF' WHERE c1 = 1;
Row 1 c2 := 'ABC'
Row 1 c2 := 'DEF'
DELETE FROM t1 WHERE c1 = 1;
Row 1 c1 := 1 c2 := 'DEF'
SELECT c2 FROM t1 WHERE c1 = 1 FOR UPDATE;
Unlock row 1
Lock row 1
Note that INSERT statements generate minimal undo

23. Redo Record Example
This is an example of a redo log dump for a single row update
UPDATE t1 SET c2 = 20 WHERE c1 = 1;
The previous value of column c2 for this row was 10
The redo record starts with a header
REDO RECORD - Thread:1 RBA: 0x003e cc LEN: 0x00f8 VLD: 0x01 SCN: 0x0000.0ac73691 SUBSCN: 1 06/26/ :40:14
This redo record is 248 (0xF8) bytes in length

24. Redo Record Example (Continued)
Change 1 updates the undo block
CHANGE #1 TYP:0 CLS:26 AFN:3 DBA:0x00c04ab7 SCN:0x0000.0ac73690 SEQ: 2 OP:5.1 ktudb redo: siz: 104 spc: 1860 flg: 0x0022 seq: 0x233f rec: 0x xid: 0x b b ktubu redo: slt: 11 rci: 1 opc: 11.1 objn: objd: tsn: 4 Undo type: Regular undo Undo type: Last buffer split: No Tablespace Undo: No x KDO undo record: KTB Redo op: 0x02 ver: 0x01 op: C uba: 0x00c04ab7.233f.01 KDO Op code: URP row dependencies Disabled xtype: XA bdba: 0x0144d022 hdba: 0x0144d021 itli: 1 ispac: 0 maxfr: 1177 tabn: 0 slot: 2(0x2) flag: 0x2c lock: 0 ckix: 0 ncol: 2 nnew: 1 size: 0 col 1: [ 2] c1 0b

25. Redo Record Example (Continued)
Change 2 updates the data block
CHANGE #2 TYP:0 CLS: 1 AFN:5 DBA:0x0144d022 SCN:0x0000.0ac73690 SEQ: 1 OP:11.5 KTB Redo op: 0x02 ver: 0x01 op: C uba: 0x00c04ab7.233f.02 KDO Op code: URP row dependencies Disabled xtype: XA bdba: 0x0144d022 hdba: 0x0144d021 itli: 1 ispac: 0 maxfr: 1177 tabn: 0 slot: 2(0x2) flag: 0x2c lock: 1 ckix: 0 ncol: 2 nnew: 1 size: 0 col 1: [ 2] c1 15

26. Row Operations Row operations generate layer 11 redo Opcodes include
Mnemonic
Description
11.2
IRP
Insert Single Row
11.3
DRP
Delete Single Row
11.4
LKR
Lock Row
11.5
URP
Update Row
11.6
ORP
Chained Row
11.9
CKI
Cluster key index
11.10
SKL
Set cluster key pointers
11.11
QMI
Insert Multiple Rows
11.12
QMD
Delete Multiple Rows

27. Single Row Insert Statements Redo
COMMIT
5.4
REDO #3
UNDO #3
11.2
5.1
UNDO #2
REDO #2
REDO #1
UNDO #1
HEADER
5.2
-- Statement #1 INSERT INTO t1 VALUES (1);
-- Statement #2 INSERT INTO t1 VALUES (2);
-- Statement #3 INSERT INTO t1 VALUES (3);
COMMIT;

28. Multi Row Insert Statements Redo
HEADER
5.2
-- Statement #1 INSERT INTO t1 SELECT * FROM t2;
UNDO #1
5.1
REDO #1
11.11
COMMIT;
COMMIT
5.4

29. Single Row Update Statements Redo
-- Statement #1 UPDATE t1 SET c2 = c2 + 1 WHERE c1 = 1;
REDO #1
UNDO #1
HEADER
11.5
5.1
5.2
-- Statement #2 UPDATE t1 SET c2 = c2 + 1 WHERE c1 = 2;
UNDO #2
REDO #2
5.1
11.5
-- Statement #3 UPDATE t1 SET c2 = c2 + 1 WHERE c1 = 3;
REDO #3
UNDO #3
11.5
5.1
COMMIT;
COMMIT
5.4

30. Multi Row Update Statements Redo
COMMIT
5.4
REDO #3
UNDO #3
11.5
5.1
UNDO #2
REDO #2
REDO #1
UNDO #1
HEADER
5.2
-- T1 contains 3 rows UPDATE t1 SET c2 = c2 + 1;
COMMIT;

31. Single Row Delete Statements Redo
-- Statement #1 DELETE FROM t1 WHERE c1 = 1;
REDO #1
UNDO #1
HEADER
11.3
5.1
5.2
-- Statement #2 DELETE FROM t1 WHERE c1 = 2;
UNDO #2
REDO #2
5.1
11.3
-- Statement #3 DELETE FROM t1 WHERE c1 = 3;
REDO #3
UNDO #3
11.3
5.1
COMMIT;
COMMIT
5.4

32. Multi Row Delete Statements Redo -- T1 contains 3 rows DELETE FROM t1;
COMMIT
5.4
REDO #3
UNDO #3
11.3
5.1
UNDO #2
REDO #2
REDO #1
UNDO #1
HEADER
5.2
-- T1 contains 3 rows DELETE FROM t1;
COMMIT;

33. Single Row Select For Update
Statements
Redo
-- Statement #1 SELECT c2 FROM t1 WHERE c1 = 1 FOR UPDATE;
REDO #1
UNDO #1
HEADER
11.4
5.1
5.2
-- Statement #2 UPDATE t1 SET c2 = c2 + 1 WHERE c1 = 1;
UNDO #2
REDO #2
5.1
11.5
COMMIT;
COMMIT
5.4

34. Multi Row Select For Update
Statements
Redo
COMMIT
5.4
REDO #3
UNDO #3
11.4
5.1
UNDO #2
REDO #2
REDO #1
UNDO #1
HEADER
5.2
-- T1 contains 3 rows SELECT c2 FROM t1 FOR UPDATE;
COMMIT;

35. Rollback Statements Redo -- Statement #1 INSERT INTO t1 VALUES (1);
UNDO #1
HEADER
11.2
5.1
5.2
-- Statement #2 INSERT INTO t1 VALUES (2);
UNDO #2
REDO #2
5.1
11.2
REDO #3
UNDO #3
5.6
11.3
ROLLBACK;
REDO #4
UNDO #4
5.11
11.3
COMMIT
5.4

36. Global Temporary Tables
Statements
Redo
COMMIT
5.4
REDO #3
UNDO #3
11.2
5.1
UNDO #2
REDO #2
UNDO #1
HEADER
REDO #1
5.2
-- Statement #1 INSERT INTO t1 VALUES (1);
-- Statement #2 INSERT INTO t1 VALUES (2);
-- Statement #3 INSERT INTO t1 VALUES (3);
COMMIT;

37. Index Operations Index operations generate layer 10 redo
Opcodes include
Opcode
Description
10.2
Insert Leaf Row
10.3
Purge Leaf Row
10.4
Delete Leaf Row
10.5
Restore Leaf Log
10.6
Lock block
10.7
Clear block opcode on commit
10.8
Initialise header
10.9
Apply XAT do to ITL 1
10.10
Set leaf block next pointer
10.11
Set leaf block previous pointer
10.12
Initialize root block after split
Opcode
Description
10.13
Make leaf block empty
10.15
Insert branch row
10.16
Purge branch row
10.18
Update key data in row
10.19
Clear split flag
10.21
Undo branch operation
10.22
Undo leaf operation
10.24
Shrink ITL
10.30
Update nonkey value
10.31
Create/Load Index
10.34

38. Index Insert Statements Redo
-- Insert into table t1 INSERT INTO t1 VALUES (1,10);
REDO #1
UNDO #1
HEADER
11.2
5.1
5.2
UNDO #2
REDO #2
5.1
10.2
-- Insert into index i1
-- Insert into index i2
REDO #3
UNDO #3
10.2
5.1
This example is based on the following objects
CREATE TABLE t1 (c1 NUMBER);
CREATE INDEX i1 ON t1 (c1);
COMMIT;
COMMIT
5.4

39. Index Updates Statements Redo
-- Update table t1 UPDATE t1 SET c1 = 2 WHERE c1 = 1;
REDO #1
UNDO #1
HEADER
11.5
5.1
5.2
UNDO #2
REDO #2
5.1
10.4
-- Delete from index i1
REDO #3
UNDO #3
10.2
5.1
-- Insert into index i1
COMMIT;
COMMIT
5.4

40. Index Deletes Statements Redo
-- Delete from table t1 DELETE FROM t1 WHERE c1 = 1;
REDO #1
UNDO #1
HEADER
11.3
5.1
5.2
UNDO #2
REDO #2
5.1
10.4
-- Delete from index i1
REDO #3
UNDO #3
10.4
5.1
-- Delete from index i2
COMMIT;
COMMIT
5.4

41. Conditional Index Updates
Before 1 After 2
Before 1 After 1
Before 1 After NULL
Before NULL After 1
UPDATE t1 SET c1 = 2 WHERE c1 = 1;
UPDATE t1 SET c1 = 1 WHERE c1 = 1
UPDATE t1 SET c1 = NULL WHERE c1 = 1;
UPDATE t1 SET c1 = 1 WHERE c1 IS NULL
Update table row
UNDO #1
5.1
REDO #1
11.5
UNDO #1
5.1
REDO #1
11.5
UNDO #1
5.1
REDO #1
11.5
UNDO #1
5.1
REDO #1
11.5
Delete index row
UNDO #2
5.1
REDO #2
10.4
UNDO #2
5.1
REDO #2
10.4
Insert index row
UNDO #3
5.1
REDO #3
10.2
UNDO #3
5.1
REDO #3
10.2

42. Block Cleanout
Occurs when ITL on data block has not been updated when changes were committed
REDO RECORD - Thread:1 RBA: 0x ac LEN: 0x003c VLD: 0x01 SCN: 0x eb3219 SUBSCN: 1 05/08/ :53:41 CHANGE #1 TYP:2 CLS: 1 AFN:5 DBA:0x0142fca2 SCN:0x eb3201 SEQ: 1 OP:4.1 Block cleanout record, scn: 0x eb3219 ver: 0x01 opt: 0x02, entries follow... itli: 2 flg: 2 scn: 0x eb3201
Block Cleanout redo
Can be generated by SELECT statements
Opcode 4.1
requires 60 byte redo record for each block

43. Backups If hot backups are in use, when backup mode is enabled
ALTER TABLESPACE <tablespace_name> BEGIN BACKUP;
A block image is written to the redo log for each block that is modified (opcode 18.1)
REDO RECORD - Thread:1 RBA: 0x003e3b LEN: 0x0818 VLD: 0x01 SCN: 0x0000.0ac84345 SUBSCN: 1 06/27/ :06:06 CHANGE #1 TYP:3 CLS: 1 AFN:5 DBA:0x014343c2 SCN:0x0000.0ac8433d SEQ: 1 OP:18.1 Log block image redo entry
When backup mode is disabled
ALTER TABLESPACE <tablespace_name> END BACKUP;
an end backup marker is written to redo log (17.1)
REDO RECORD - Thread:1 RBA: 0x003e3b c.0010 LEN: 0x0038 VLD: 0x01 SCN: 0x0000.0ac84347 SUBSCN: 1 06/27/ :06:09 CHANGE #1 MEDIA RECOVERY MARKER SCN:0x SEQ: 0 OP:17.1 End backup marker - file:5 scn: 0x0000.0ac84341

44. Block Writes
In Oracle and above blocks written from buffer cache to disk by DBWR are recorded in redo logs
Supports fast recovery
REDO RECORD - Thread:1 RBA: 0x003e LEN: 0x2948 VLD: 0x02 SCN: 0x0000.0ac8289c SUBSCN: 1 06/27/ :19:44 CHANGE #1 MEDIA RECOVERY MARKER SCN:0x SEQ: 0 OP:23.1 Block Written - afn: 5 rdba: 0x014238ad(5,145581) scn: 0x0000.0ac82889 seq: 0x07 flg:0x04 Block Written - afn: 5 rdba: 0x014238ac(5,145580) scn: 0x0000.0ac82889 seq: 0x08 flg:0x04 Block Written - afn: 5 rdba: 0x014238ab(5,145579) scn: 0x0000.0ac82889 seq: 0x07 flg:0x04 Block Written - afn: 5 rdba: 0x014238aa(5,145578) scn: 0x0000.0ac82889 seq: 0x07 flg:0x04
Each block record is 32 bytes in length (OS dependent)

45. Direct Loads
If archiving is enabled then direct load blocks are written to redo
In Oracle 9.2 each block requires a 19.1 and 24.2 change
REDO RECORD - Thread:1 RBA: 0x003e LEN: 0x0848 VLD: 0x01 SCN: 0x0000.0ac83828 SUBSCN: 1 06/27/ :21:50 CHANGE #1 TYP:1 CLS: 1 AFN:5 DBA:0x0142b962 SCN:0x0000.0ac83826 SEQ: 1 OP:19.1 Direct Loader block redo entry Block header dump: 0x0e5c0000 Object id on Block? Y seg/obj: 0x4bd9 csc: 0x00.ac itc: 3 flg: - typ: 1 – DATA fsl: 0 fnx: 0x0 ver: 0x01 Itl Xid Uba Flag Lck Scn/Fsc# 0x01 0x x fsc 0x x02 0x x fsc 0x x03 0x x fsc 0x
-- Block dump follows
CHANGE #2 MEDIA RECOVERY MARKER SCN:0x SEQ: 0 OP:24.2

46. NOLOGGING Redo generation can be disabled for some operations using
UNRECOVERABLE (Oracle 7)
NOLOGGING (Oracle 8.0 and above)
Can be enabled for specific tables and indexes at
object level
statement level
The following redo log entry indicates a range of blocks which cannot be recovered
NOLOGGING at statement level overrides NOLOGGING at object level.
Other NOLOGGING operations include
ALTER TABLE MOVE PARTITION
ALTER TABLE SPLIT PARTITION
ALTER INDEX SPLIT PARTITION
ALTER INDEX REBUILD
ALTER INDEX REBUILD PARTITION
REDO RECORD - Thread:1 RBA: 0x e0 LEN: 0x0028 VLD: 0x01 SCN: 0x ebaeec SUBSCN: 1 05/09/ :16:07 CHANGE #1 INVLD AFN:5 DBA:0x0142ff03 BLKS:0x001f SCN:0x ebaeec SEQ: 1 OP:19.2 Direct Loader invalidate block range redo entry

47. NOLOGGING
These tests were performed on an ARCHIVELOG database using a row table
Operation
LOGGING
NOLOGGING
CREATE TABLE AS SELECT
39548
ALTER TABLE MOVE
45340
INSERT /*+ APPEND */
42452
CREATE MATERIALIZED VIEW
CREATE INDEX
24548
ALTER INDEX REBUILD
32192
ALTER INDEX REBUILD ONLINE
67840
SQL*Loader (Direct)
56712
Online Reorganization
Redo size in bytes
Median size from 3 runs

48. FORCE NOLOGGING Objects created using NOLOGGING cannot be recovered
Backup should be taken immediately affect using NOLOGGING
In Oracle 9.2 and above NOLOGGING can be disabled using
STARTUP MOUNT ALTER DATABASE FORCE LOGGING; or
ALTER TABLESPACE <tablespace_name> FORCE LOGGING;

49. Transaction Auditing Introduced in Oracle 8.1.5 to support Log Miner
Enabled by default
Each session includes 5.19 change vector
CHANGE #4 MEDIA RECOVERY MARKER SCN:0x SEQ: 0 OP:5.19 session number = 9 serial number = 5 current username = US01 login username = US01 client info = OS username = BMC.COM\jdyke Machine name = BMC.COM\JDYKE-ABI-EU OS terminal = JDYKE-ABI-EU OS process id = 1784:1724 OS program name = sqlplusw.exe transaction name =
Last change of first redo record in session
Record length is variable

50. Transaction Auditing
Each subsequent transaction includes 5.20 change vector
CHANGE #4 MEDIA RECOVERY MARKER SCN:0x SEQ: 0 OP:5.20 session number = 9 serial number = 5 transaction name =
Last change of second and subsequent redo records in session
Record length is variable
If LogMiner is not in use, transaction auditing can be disabled by setting initialisation parameter
TRANSACTION_AUDITING = FALSE;

51. Supplemental Logging
Introduced in Oracle to enable LogMiner to support
Chained rows
Cluster keys
Extended in Oracle 9.2 to support Oracle Streams
Used with logical standby databases
ROWIDs may differ therefore cannot be used
Allows updated rows to be identified logically
Can be specified at
Database level
Table level
Enabled by default in 9.0.1; disabled by default in 9.2.0

52. Supplemental Logging At database level can enable
minimal supplemental logging
ALTER DATABASE ADD SUPPLEMENTAL LOG DATA;
identification key supplemental logging
ALTER DATABASE ADD SUPPLEMENTAL LOG DATA (PRIMARY KEY) COLUMNS;
ALTER DATABASE ADD SUPPLEMENTAL LOG DATA (UNIQUE KEY) COLUMNS;
ALTER DATABASE ADD SUPPLEMENTAL LOG DATA (PRIMARY KEY, UNIQUE INDEX) COLUMNS;
Disabled using
ALTER DATABASE DROP SUPPLEMENTAL LOG DATA;
Oracle selects a subset of columns to include in the redo log
Not necessarily unique

53. Supplemental Logging At table level columns must be specified
If ALWAYS keyword is specified, all specified columns will be logged for every update
ALTER TABLE table1 ADD SUPPLEMENTAL LOG GROUP group1 (c2,c3) ALWAYS;
Otherwise specified columns are only logged if one of them is updated
ALTER TABLE table1 ADD SUPPLEMENTAL LOG GROUP group1 (c2,c3);
Disabled using
ALTER TABLE table1 DROP SUPPLEMENTAL LOG GROUP group1;
See data dictionary views
DBA_LOG_GROUPS
DBA_LOG_GROUP_COLUMNS

54. Supplemental Logging Additional columns are appended to undo data
CREATE TABLE t1 (c1 NUMBER,c2 NUMBER,c3 NUMBER); INSERT INTO t1 VALUES (100, 200, 300);
ALTER TABLE table1 ADD SUPPLEMENTAL LOG GROUP group1 (c1,c2,c3) ALWAYS;
Statements
Redo
-- Statement #1 UPDATE t1 SET c3 = 400 WHERE c1 = 100;
HEADER
5.2
REDO #1
11.5
c3 = 400
UNDO #1
5.1
c3 = 300
c2 = 200
c1 = 100
HEADER
5.2

55. Dumping Logfiles To dump the contents of a logfile use
ALTER SYSTEM DUMP LOGFILE 'pathname';
A range of data file blocks can be specified
ALTER SYSTEM DUMP LOGFILE 'pathname'; DBA MIN <fileno> . <blockno> DBA MAX <fileno> . <blockno>
A range of redo byte addresses can be specified
ALTER SYSTEM DUMP LOGFILE 'pathname'; RBA MIN <logfile> . <sequenceno> RBA MAX <logfile> . <sequenceno>
A layer and (optional) opcode can be specified
ALTER SYSTEM DUMP LOGFILE 'pathname'; LAYER <integer> OPCODE <integer>

56. Thank you for your interest
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