Oracle data storage: ROWIDs

About Rowids

• ROWIDs uniquely identifiy a row in the database. (although there are some exceptions).
• ROWID may refer to a datatype and a pseudocolumn. In its different forms it is a representation of the physical location of a row within the database.
• The ROWID for a row can change as the result of dumping and reloading the database.
• For this reason ROWID values should not be used across transaction lines.
• You cannot set the value of a ROWID pseudocolumn.
• ROWID is not physically stored in the database.It is inferred from the file and block address of the data.

ROWIDs are used in the construction of indexes. In addition to this,

• Rowids are the fastest means of accessing particular rows.
• Rowids provide the ability to see how a table is organized.
• Rowids are unique identifiers for rows in a given table.

Types of ROWIDs: Physical Rowid, Logical Rowid and Foreign Rowid

Physical ROWIDs:

• Store the addresses of rows in heap-organized tables, clustered tables, and table and index partitions.
• Provide the fastest access to a row.
• Contain the physical address of a row and allow its retrieval in a single block access.
• Rowid corresponds to the physical address of a row's row piece (or the initial row piece if the row is chained in multiple row pieces).
• In case of clustered tables, rows in different tables that are in the same data block can have the same rowid.
• Physical rowids have two formats: restricted and extended.

• In a logical rowid, a physical guess identifies the block in which a row was stored at the time the guess is made, and the database uses the guess to search the block directly.
• However, as new rows are inserted, guesses can become stale.
• Guess staleness can be monitored with DBMS_STATS (index statistics capture the percentage of rows with valid guesses).
• Statistic stored in the DBA_INDEXES (PCT_DIRECT_ACCESS column).
• To refresh guess information:
• Rebuild secondary indexes (resource intensive).
• ALTER INDEX...UPDATE BLOCK REFERENCES

Logical ROWIDs:

• Strore the addresses of rows in index-organized tables (IOTs).
• Used in index-organized tables (IOT), these are based on the table's primary key.
• Logical rowids change when the IOT's primary key is updated.
• This is because table data is stored in the index leaves and thus do not have a permanent physical address.
• Indexes that use logical rowids include a physical guess, which identifies the block location of the row in the IOT at the time the guess was made.
• Since logical rowids do not indicate the exact physical location of a row, they cannot be used to see how a table is organized.

Restricted x Extended ROWIDs

Restricted ROWIDs:

• Provided for backward compatibility with applications developed with Oracle 7 and earlier
• Until Oracle 7, ROWIDs used 8 bytes
• The old format is known as Restricted rowid format.
• Restricted ROWID format stores (block number, Row number, file number)

Restricted Rowid (8 bytes) Block# (bytes 1-4).Row#(bytes 5-6).File#(bytes 7-8)

Extended ROWIDs

• Starting with Oracle 8 Rowid's format changed.
• Extended rowid: four-piece format.
• Uses a base 64 encodig (A-Z,a-z,0-9,+,/)
• It is now 10 bytes long and includes the ID of the Object to which the row belongs.
• Until Oracle 7 file numbers were unique within a database.
• With the new format, ROWIDs stores the relative file number (the file number within the tablespace in which the object is stored).
• Until Oracle 7, the 2-byte representation of file numbers limited the maximum number of files a database could have to 65533.
• This limit now is for the number of files each tablespace can have.
• An extended rowid includes a data object number. This rowid type uses a base 64 encoding of the physical address for each row.

AAAC9E: The data object number identifies the segment. Note: A data object number is assigned to every database segment (table, index, etc). HOWEVER, Schema objects in the same segment (such as a table cluster) have the SAME Object ID. AAE: The data file number: Tablespace-relative. Identifies the file that contains the row. AAAABX: The data block number Identifies the block that contains the row. Relative to the datafile. AAA: The row number: identifies the row in the block. ObjID(bytes 1-4) . RelativeFN(byte 5 + 4bits) . Block#(4bits + byte 7) . Row#(bytes 9-10)

ROWID Pseudocolumn

• Every Oracle table has a pseudocolumn named ROWID. Its value, however, is not actually stored in the table.
• You can select from pseudocolumns, but you cannot insert, update, or delete their values.
• Values of the ROWID pseudocolumn are strings representing ,in hexadecimal format, the address of each row.
• You can parse the value returned from rowid to understand the physical storage of rows in the database.

(a) Query the extended rowid

SQL> select rowid, last_name from hr.employees where employee_id=100;

ROWID               LAST_NAME
------------------  -----------
AAAR5VAAFAAAADPAAA  King

(b) To see the old rowid format (restricted rowid), you can use the DBMS_ROWID package:

SQL> select dbms_rowid.rowid_to_restricted(rowid,1) old_rowid
  2  from hr.employees
  3* where employee_id = 100


OLD_ROWID
------------------
000000CF.0000.0005

Restriced rowid format:
000000CF: data block that contains the row.
Block numbers are relative to the datafile, not tablespace.
0000: row numbers start with 0.
0005: data file that contains the row.

• With the restricted format, to find out the segment (table, index) a rowid belonged to it was necessary to compare ROWID's block and file numbers with entries in the DBA_EXTENTS view.
• With extended format, you can use DBMS_ROWID as below:

SQL> select first_name, dbms_rowid.rowid_object(rowid) "ObjectID",
  2                     dbms_rowid.rowid_relative_fno(rowid) "File#",
  3                     dbms_rowid.rowid_block_number(rowid) "Block#",
  4                     dbms_rowid.rowid_row_number(rowid)   "Row#"
  5  from hr.employees
  6  where employee_id = 100;

FIRST_NAME        ObjectID      File#     Block#     Row#
-------------------- ---------- ---------- ---------- ----------
Steven     73301   5   207        0

Now query DBA_OBJECTS to find out what database object the row belongs to

SQL> select owner, object_name, object_type, data_object_id, object_id
  2  from dba_objects
  3* where data_object_id =  73301;

OWNER       OBJECT_NAME     OBJECT_TYPE    DATA_OBJECT_ID  OBJECT_ID
----------- --------------- -------------- --------------- ----------
HR          EMPLOYEES       TABLE          73301           73933

When does a ROWID change?

• If row movement is enabled: ROWID can change because of partition key updates, Flashback Table operations, shrink table operations, and so on.
• If row movement is disabled: ROWID can change if the row is exported and imported using Oracle Database utilities

Can you use ROWIDs as a table's primary key?

• No. Oracle won't let you create a PK constraint on a rowid column.
• In addition, besides not being always unique (rows in clustered tables may share a rowid), a row's rowid can change (i.e., after and export/import or partition movement operation).

Can I store ROWIDs in a table column?

• Yes. You can create table column using the ROWID data type.
• However, ROWID values should not be used across transaction lines.
• Storing a rowid with the intent of using it latter (i.e. as an audit trail record), may lead to errors and incorrect information, since rowids may change as the result of:
  
  • Export/import operation
  • ALTER TABLE...MOVE
  • ALTER TABLE...SHRINK SPACE
  • FLASHBACK TABLE...
  • Partition operation (split, combination)
  • Data update that results in row being moved to another partition

Using Log Miner (II) - Example

Example 1: Find all modifications in the last archived redo log Mining and source db are the same Using Online catalog as dictionary Steps: (the various steps are part of a script file logmnr_sql.sh) Configure supplemental logs and NLS_DATE_FORMAT (optional) Get user credentials (UserA, UserB, System) UserA creates table UserA.EMP UserA updates rows on table UserA.EMP UserB updates rows on table UserA.EMP User System: (a) archives current redo log; (b) Add list of log files for mining; (c) starts log miner; (d) query log miner information; and (e) Ends log miner section

(Initial configuration): Enable supplemental logging and set data format

SQL> alter database add supplemental log data;
SQL> alter session set nls_date_format = 'dd-mon-yyyy hh24:mi:ss';

(1) Get user credentials (UserA, UserB, System)

#!/bin/bash
# logmnr_sql.sh

LOGFILE=logminer.log

###############################################################
# Get users credentials
##############################################################

usersystem=system
echo "Enter password for system"
read -s passwds
usera=usera
echo "Enter password for usera"
read -s passwda
userb=userb
echo "Enter password for userb"
read -s passwdb
sid=${ORACLE_SID}
(cont..)

(2) UserA creates table UserA.EMP

(cont..)
###############################################################
# Log in as userA. Recreate EMP table
##############################################################

sqlplus -s /nolog << EndOfSQL >> ${LOGFILE}
connect ${usera}/${passwda} 
whenever sqlerror exit sql.sqlcode;

prompt "Connected: UserA - recreating EMP.."

drop table emp;
create table emp as
  select employee_id as empno,
         first_name || ' ' || last_name as ename,
         department_id as deptno,
         salary as salary
  from hr.employees;
grant select, update on emp to userb;

exit;
EndOfSQL

ERRORCODE=$?

#check the return code from SQL Plus
if [ $ERRORCODE != 0 ]
then
 echo ********************************
 echo "ERROR: SQL*Plus failed with error code: $ERRORCODE"
else
 echo ********************************
 echo "SQL*Plus completed successfully. Error code: $ERRORCODE"
fi
(cont..)

(3) UserA updates some rows on table UserA.EMP

(cont..)
###############################################################
# Log in as usera. update data on table EMP
##############################################################

sqlplus -s /nolog << EndOfSQL >> ${LOGFILE}
connect ${usera}/${passwda} 
whenever sqlerror exit sql.sqlcode;

prompt "Connected: UserA - Updating rows..."

set serveroutput on  
begin
  update emp set salary = salary*1.05 where deptno = 50;
  commit;
  dbms_output.put_line('salaries on dept 50 updated..');  
  declare
   cursor c_emp is
     select empno, ename, deptno, salary from emp
     where deptno = 30
     for update;
  begin
   for c_reg in c_emp loop
     update emp
      set ename = initcap(c_reg.ename)
      where current of c_emp;
     update emp
      set salary = c_reg.salary *1.10
      where current of c_emp;
   end loop;
   commit;
   dbms_output.put_line('names and salaries on dept 30 updated..');  
  end;
end;
/

exit;
EndOfSQL

ERRORCODE=$?

# Check the return code from SQL Plus
if [ $ERRORCODE != 0 ]
then
 echo ********************************
 echo "ERROR: SQL*Plus failed with error code: $ERRORCODE"
else
 echo ********************************
 echo "SQL*Plus completed successfully. Error code: $ERRORCODE"
fi
(cont..)

(4) UserB updates rows on table UserA.EMP

###############################################################
# Log in as userB. update data on table EMP
##############################################################

sqlplus -s /nolog << EndOfSQL >> ${LOGFILE}
connect ${userb}/${passwdb} 
whenever sqlerror exit sql.sqlcode;

prompt "Connected: USERB"

set serveroutput on  
begin
  update usera.emp set salary = salary*1.05 where deptno = 60;
  dbms_output.put_line('SQL%ROWCOUNT: ['|| SQL%ROWCOUNT || '] rows returned');
  commit;
  dbms_output.put_line('salaries on dept 60 updated..');  
  declare
   cursor c_emp2 is
     select empno, ename, deptno, salary from usera.emp
     where deptno = 90
     for update;
  begin
   for c_reg in c_emp2 loop
     update usera.emp
      set ename = initcap(c_reg.ename)
      where current of c_emp2;
     update usera.emp
      set salary = c_reg.salary *1.10
      where current of c_emp2;
   end loop;
   commit;
   dbms_output.put_line('names and salaries on dept 30 updated..');  
  end;
end;
/
exit;
EndOfSQL

ERRORCODE=$?

# Check the return code from SQL Plus
if [ $ERRORCODE != 0 ]
then
 echo ********************************
 echo "ERROR: SQL*Plus failed with error code: $ERRORCODE"
else
 echo ********************************
 echo "SQL*Plus completed successfully. Error code: $ERRORCODE"
fi
(cont..)

(5) Log in as SYSTEM: (a) archives current redo log; (b) Add list of log files for mining; (c) starts log miner; (d) query log miner information; and (e) Ends log miner section

###############################################################
# Log in as SYSTEM. Run Log Miner 
##############################################################
echo "Configuring Log Miner section..."

sqlplus -s /nolog << EndOfSQL >> ${LOGFILE}
connect ${usersystem}/${passwds} 
whenever sqlerror exit sql.sqlcode;

prompt "Connected: SYSTEM"


prompt " (a) Switching current log file.."
alter system archive log current;

prompt "Most recently archived log file is"
set linesize 150
select name, first_change# from v\$archived_log
 where first_time = (select max(first_time) 
                       from v\$archived_log);

prompt "(b) Configuring the list of redo log files to be mined.."

declare
  v_logname varchar2(200);
begin
  select name into v_logname
   from v\$archived_log
   where first_time = (select max(first_time) 
                         from v\$archived_log);
 dbms_logmnr.add_logfile(LOGFILENAME => v_logname, OPTIONS => dbms_logmnr.new);
end;
/

prompt "List of log files added to log miner: "
select   to_char(low_time, 'dd-mon-yy hh24:mi:ss') lowtime,
         to_char(high_time, 'dd-mon-yy hh24:mi:ss') hightime,
         type, filesize/1024/1024 Mb, filename 
from v\$logmnr_logs;

prompt "(c) Starting log miner using online catalog.."
execute dbms_logmnr.start_logmnr(options => dbms_logmnr.dict_from_online_catalog);

prompt "(d) Querying log miner results"

set linesize 150
set pagesize 80
column usr format a10
column osusr format a10
column machine_name format a10
column xid format a12
col operation format a15
col table_name format a10
col sql_redo format a30
col sql_undo format a30

select username as usr,
       os_username as osusr,
       (xidusn ||'.'|| xidslt ||'.'||xidsqn) as xid,
       operation, 
       table_name,
       sql_redo, 
       sql_undo
  from v\$logmnr_contents
  where username in ('USERA', 'USERB');

USR     OSUSR    XID        OPERATION       TABLE_NAME  SQL_REDO                       SQL_UNDO
------  -------- ---------- --------------- ----------  ------------------------------ ------------------------------
USERA   jdoe     10.12.988  START                       set transaction read write;
USERA   jdoe     1.7.928    DDL              EMP        ALTER TABLE "USERA"."EMP" RENA
                                                        ME TO "BIN$sKOUXNE/r7TgQAB/AQE
                                                        yrA==$0" ;
...
USERA   jdoe     1.7.928    DDL              EMP        drop table emp AS "BIN$sKOUXNE
                                                        /r7TgQAB/AQEyrA==$0" ;
...
USERA   jdoe     4.32.983   DDL              EMP       create table emp as
                                                        select employee_id as empno,
                                                        first_name || ' ' ||
                                                        last_name as ename,
                                                        department_id as deptno,
                                                        salary as salary
                                                        from hr.employees;
..
USERA   jdoe     4.23.984   START                       set transaction read write;
USERA   jdoe     4.32.983   DIRECT INSERT    EMP        insert into "USERA"."EMP"("EMP delete from "USERA"."EMP" wher
                                                        NO","ENAME","DEPTNO","SALARY") e "EMPNO" = '198' and "ENAME"
                                                        values ('198','Donald OConnel  = 'Donald OConnell' and "DEPTN
                                                        l','50','2600');               O" = '50' and "SALARY" = '2600
                                                                                       ' and ROWID = 'AAASdlAAEAAAAMb
                                                                                       AAA';

...
USERA   jdoe     4.32.983   DIRECT INSERT   EMP         insert into "USERA"."EMP"("EMP delete from "USERA"."EMP" wher
                                                        NO","ENAME","DEPTNO","SALARY") e "EMPNO" = '197' and "ENAME"
                                                        values ('197','Kevin Feeney',  = 'Kevin Feeney' and "DEPTNO"
                                                        '50','3000');                  = '50' and "SALARY" = '3000' a
                                                                                       nd ROWID = 'AAASdlAAEAAAAMbABq
                                                                                       ';
...
USERA   jdoe     10.31.988  DDL             EMP         grant select, update on emp to
                                                        userb;
...
USERA   jdoe     10.31.988  UPDATE          OBJ$        update "SYS"."OBJ$" set "OBJ#" update "SYS"."OBJ$" set "OBJ#"
                                                        = '75621', "DATAOBJ#" = '7562  = '75621', "DATAOBJ#" = '7562
                                                        1', "TYPE#" = '2', "CTIME" = T 1', "TYPE#" = '2', "CTIME" = T
                                                        O_DATE('22-NOV-10', 'DD-MON-RR O_DATE('22-NOV-10', 'DD-MON-RR
                                                        '), "MTIME" = TO_DATE('22-NOV- '), "MTIME" = TO_DATE('22-NOV-
                                                        10', 'DD-MON-RR'), "STIME" = T 10', 'DD-MON-RR'), "STIME" = T
                                                        O_DATE('22-NOV-10', 'DD-MON-RR O_DATE('22-NOV-10', 'DD-MON-RR
                                                        '), "STATUS" = '1', "FLAGS" =  '), "STATUS" = '1', "FLAGS" =
                                                        '0', "OID$" = NULL, "SPARE1" = '0', "OID$" = NULL, "SPARE1" =
                                                        '6', "SPARE2" = '1' where "OB  '6', "SPARE2" = '1' where "OB
                                                        J#" = '75621' and "DATAOBJ#" = J#" = '75621' and "DATAOBJ#" =
                                                        '75621' and "OWNER#" = '92' a  '75621' and "OWNER#" = '92' a
                                                        nd "TYPE#" = '2' and "CTIME" = nd "TYPE#" = '2' and "CTIME" =
                                                        TO_DATE('22-NOV-10', 'DD-MON-  TO_DATE('22-NOV-10', 'DD-MON-
                                                        RR') and "MTIME" = TO_DATE('22 RR') and "MTIME" = TO_DATE('22
                                                        -NOV-10', 'DD-MON-RR') and "ST -NOV-10', 'DD-MON-RR') and "ST
                                                        IME" = TO_DATE('22-NOV-10', 'D IME" = TO_DATE('22-NOV-10', 'D
                                                        D-MON-RR') and "STATUS" = '1'  D-MON-RR') and "STATUS" = '1'
                                                        and "FLAGS" = '0' and "OID$" I and "FLAGS" = '0' and "OID$" I
                                                        S NULL and "SPARE1" = '6' and  S NULL and "SPARE1" = '6' and
                                                        "SPARE2" = '1' and ROWID = 'AA "SPARE2" = '1' and ROWID = 'AA
                                                        AAASAABAAAU6JAAi';             AAASAABAAAU6JAAi';
..
USERA   jdoe     10.31.988    COMMIT                    commit;
USERA   jdoe     7.26.985     START                     set transaction read write;
...
USERA   jdoe     3.23.1299    START                     set transaction read write;
USERA   jdoe     3.23.1299    UPDATE    EMP          update "USERA"."EMP" set "SALA update "USERA"."EMP" set "SALA
                                                        RY" = '2730' where "EMPNO" = ' RY" = '2600' where "EMPNO" = '
                                                        198' and "ENAME" = 'Donald OCo 198' and "ENAME" = 'Donald OCo
                                                        nnell' and "DEPTNO" = '50' and nnell' and "DEPTNO" = '50' and
                                                        "SALARY" = '2600' and ROWID =  "SALARY" = '2730' and ROWID =
                                                        'AAASdlAAEAAAAMbAAA';          'AAASdlAAEAAAAMbAAA';
...
USERA   jdoe     3.23.1299    UPDATE    EMP          update "USERA"."EMP" set "SALA update "USERA"."EMP" set "SALA
                                                        RY" = '2250' where "EMPNO" = ' RY" = '3000' where "EMPNO" = '
                                                        197' and "ENAME" = 'Kevin Feen 197' and "ENAME" = 'Kevin Feen
                                                        ey' and "DEPTNO" = '50' and "S ey' and "DEPTNO" = '50' and "S
                                                        ALARY" = '3000' and ROWID = 'A ALARY" = '2250' and ROWID = 'A
                                                        AASdlAAEAAAAMbABq';            AASdlAAEAAAAMbABq';

USERA   jdoe     3.23.1299   COMMIT                     commit;
USERA   jdoe     1.12.927    START                      set transaction read write;
USERA   jdoe     1.12.92     SELECT_FOR_UPDATE EMP      select * from "USERA"."EMP" wh
                                                     ere ROWID = 'AAASdlAAEAAAAMbAA
                                                        X' for update;
...
USERA   jdoe     1.12.927    UPDATE       EMP           update "USERA"."EMP" set "ENAM update "USERA"."EMP" set "ENAM
                                                        E" = 'Den Raphaely' where "EMP E" = 'Den Raphaely' where "EMP
                                                        NO" = '114' and "ENAME" = 'Den NO" = '114' and "ENAME" = 'Den
                                                        Raphaely' and "DEPTNO" = '30'  Raphaely' and "DEPTNO" = '30'
                                                        and "SALARY" = '11000' and RO  and "SALARY" = '11000' and RO
                                                        WID = 'AAASdlAAEAAAAMbAAX';    WID = 'AAASdlAAEAAAAMbAAX';
...
USERA   jdoe     1.12.927    UPDATE       EMP           update "USERA"."EMP" set "SALA update "USERA"."EMP" set "SALA
                                                        RY" = '2750' where "EMPNO" = ' RY" = '2500' where "EMPNO" = '
                                                        119' and "ENAME" = 'Karen Colm 119' and "ENAME" = 'Karen Colm
                                                        enares' and "DEPTNO" = '30' an enares' and "DEPTNO" = '30' an
                                                        d "SALARY" = '2500' and ROWID  d "SALARY" = '2750' and ROWID
                                                        = 'AAASdlAAEAAAAMbAAc';        = 'AAASdlAAEAAAAMbAAc';

USERB   jdoe     1.12.927    COMMIT                     commit;
...
USERB   jdoe     8.21.1521   START                      set transaction read write;
USERB   jdoe     6.16.1306   UPDATE       EMP           update "USERA"."EMP" set "SALA update "USERA"."EMP" set "SALA
                                                        RY" = '9450' where "EMPNO" = ' RY" = '9000' where "EMPNO" = '
                                                        103' and "ENAME" = 'Alexander  103' and "ENAME" = 'Alexander
                                                        Hunold' and "DEPTNO" = '60' an Hunold' and "DEPTNO" = '60' an
                                                        d "SALARY" = '9000' and ROWID  d "SALARY" = '9450' and ROWID
                                                        = 'AAASdlAAEAAAAMbAAM';        = 'AAASdlAAEAAAAMbAAM';
...
USERB   jdoe     6.16.1306    COMMIT                    commit;
USERB   jdoe     4.5.983      START                     set transaction read write;
USERB   jdoe     4.5.983      SELECT_FOR_UPDA EMP       select * from "USERA"."EMP" wh
                                           TE           ere ROWID = 'AAASdlAAEAAAAMbAA
...
USERB   jdoe     4.5.983      UPDATE     EMP         update "USERA"."EMP" set "ENAM update "USERA"."EMP" set "ENAM
                                                        E" = 'Steven King' where "EMPN E" = 'Steven King' where "EMPN
                                                        O" = '100' and "ENAME" = 'Stev O" = '100' and "ENAME" = 'Stev
                                                        en King' and "DEPTNO" = '90' a en King' and "DEPTNO" = '90' a
                                                        nd "SALARY" = '24000' and ROWI nd "SALARY" = '24000' and ROWI
                                                        D = 'AAASdlAAEAAAAMbAAJ';      D = 'AAASdlAAEAAAAMbAAJ';
...
USERB   jdoe     4.5.983      COMMIT                    commit;
...
188 rows selected.

(e) End the Log Miner Section

prompt "(e) Ending log miner section.."
execute dbms_logmnr.end_logmnr();
exit;
EndOfSQL


ERRORCODE=$?

# Check the return code from SQL Plus
if [ $ERRORCODE != 0 ]
then
 echo ********************************
 echo "ERROR: SQL*Plus failed with error code: $ERRORCODE"
else
 echo ********************************
 echo "SQL*Plus completed successfully. Error code: $ERRORCODE"
fi

Using the Log Miner (I)

Using the LogMiner

• First appeared in Oracle 8i
• Log Miner allows for analysis of online and archived redo log files.
• LogMiner provides a well-defined, easy-to-use, and comprehensive relational interface to redo log files

Enhancements in Oracle 11g

• LogMiner was integrated with OEM
• Also integrated with the new flashback transaction feature
• Can be used from command line or through OEM

Possible uses:

• Find out when a logical error happened and who did it.
• This information in turn can be used to determine when to initiate time-based or change-based recovery (V$LOGMNR_CONTENTS)
• Determine what actions are needed to perform fine-grained recovery at the transaction level (flashback transaction)
• Support for trend analysis (find out which databases get most DMLs)
• Support on post-facto auditing.
• Useful to find out who has updated a given table (or set of tables).
• Explore what happens when a DML/DDL is issued against the database

Configuring the Log Miner

Four objects are used in a LogMiner configuration:

1. The Source database
2. The Mining database
3. The LogMiner dictionary - used to translate internal object identifiers to object names and external data formats.
4. Redo log files that will be analyzed

Managing LogMiner operation:

• Use SYS.DBMS_LOGMNR and SYS.DBMS_LOGMNR_D packages to (a) select redo log files for analysis, (b) begin and (c) end log miner section.
• Use V$LOGMNR_CONTENTS view to query the contents of redo logs.
• You must be connected as SYS or have EXECUTE_CATALOG_ROLE role

DBMS_LOGMNR package subprograms:

SQL> dbms_logmnr.add_logfile(LOGFILENAME => logname, OPTIONS => dbms_logmnr.new);
-- Add redo log file to a list of redo logs for LogMiner to process.

OPTIONS:
• new -- implicit call to dbms_logmnr.end_logmnr and start a new log miner session. Creates a new list and add the redo log.
• addfile -- Adds the redo log to the existing list

SQL> dbms_logmnr.remove_logfile(LOGFILENAME => logname);
-- Remove redo from list

SQL>  dbms_logmnr.start_logmnr(OPTIONS => dbms_logmnr.dict_from_online_catalog);
-- Initialized the LogMiner

OPTIONS:
• committed_data_only
• Return committed statements only. (none rolled back or in progress)
• Group statements of a committed transaction.
• Transactions returned in order.
• skip_corruption
• skips corruptions in the redo log (redo log block corruption)
• ddl_dict_tracking
• Used when dictionary is in a flat file. Updates dict references as DDL are processed
• dict_from_online_catalog
• directs log miner to use the online dictionary of the database when translating object names
• dict_from_redo_logs
• no_sql_delimiter
• Useful if you want to use the reconstructed statements directly in a open cursor
• no_rowid_in_stmt
• print_pretty_sql
• continuous_mine
• Instructs log miner to add redo log files, as needed, until find the data on the specified SCN or timestamp
• string_literals_in_stmt

SQL> dbms_logmnr.end_logmnr();
-- Finishes a LogMiner session

Requirements to use LogMiner

1. Source and Mining databases
• Both must run on the same platform
• mining db can be the same or separate from source db
• mining db must be same or later release of the source db
• mining db must use same characterset (or superset) of source db
2. LogMiner dictionary
• Must be produced from the source db
• Used to translate redo log information into a meaningful format
• Used to display table and column names instead of their internal IDs.
• Without a dictionary, LogMiner also display all values in hexadecimal format.
3. Redo Logs
• must be produced by the same source db
• associated with the same database RESETLOGS SCN
• Must be from oracle 8.0 or later (mostly 9i or later)
4. Supplemental Logging
• must be enabled before redo logs are generated
• Enable with: ALTER DATABASE ADD SUPPLEMENTAL LOG DATA;
• Logs the extra information necessary to reconstruct the SQL statement as well
  as one to revert the original action.
• Without supplemental logging instance and media recovery is possible, but log mining,
  or reconstruction of the original SQL statement, is not possible.

SQL> select supplemental_log_data_min,supplemental_log_data_pk, 
     supplemental_log_data_fk, supplemental_log_data_all
     from v$database;

SUPPLEMENTAL_LOG_DATA_MIN SUPPLEMENTAL_LOG_DATA_PK SUPPLEMENTAL_LOG_DATA_FK SUPPLEMENTAL_LOG_DATA_ALL 
------------------------- ------------------------ ------------------------ ------------------------- 
YES                       YES                      YES                      NO                       

About the LogMiner dictionary Used to translate the information in the redo log files into object names and display the data in alpha numeric, instead of hexadecimal format.

(a) You can use the online catalog of the source database

• For this, the source database must be online and available
• To use the online catalog: SQL> execute dbms_logmnr.start_logmnr( options => dbms_logmnr.dict_from_online_catalog);

(b) Can be extracted from source database into the redo log files

• Used when the source database is not available
• In order to extract dictionary information, the source database must be (1) open, (2) in archivelog mode, (3) with enabled archiving.
• To extract dictionary: SQL> execute dbms_logmnr_d.build( options => dbms_logmnr_d.store_in_redo_logs);
• The dictionary information is stored in the archived redo logs. To find out which:
• SQL> select name from v$archived_log where dictionary_begin = 'YES';
• SQL> select name from v$archived_log where dictionary_end = 'YES';

(c) Can be extracted from source db to flat file

• Available for backward compatibility only. no trasactional consistency.

Example 1: Find all modifications in the last archived redo log Mining and source db are the same Using Online catalog as dictionary