A2Z of Oracle Database Recovery

Sumit Singh Chadha — Mon, 03 Nov 2008 20:14:49 +0000

Let us look at the following recovery scenario’s :-

1. Loss of INACTIVE ONLINE Redo Log Group – COMPLETE RECOVERY.

a. CASE I – During Database Startup we notice that REDO LOG is missing and Error Came.

b. CASE II – If the INACTIVE REDO log is lost during Database Open.

2. Loss of Current Online Redo Log Group – INCOMPLETE RECOVERY

3. Loss of CONTROL FILE

4. Loss of UNDO Datafile/SYSTEM Datafile.

5. Loss of Datafile ( NON SYSTEM and NON UNDO Datafile )

——————————————————————————————————

1. Loss of INACTIVE ONLINE Redo Log Group – COMPLETE RECOVERY.

· CASE I – During Database Startup we notice that REDO LOG is missing and Error Came.

SQL> startup

ORACLE instance started.

Total System Global Area 135338868 bytes

Fixed Size 453492 bytes

Variable Size 109051904 bytes

Database Buffers 25165824 bytes

Redo Buffers 667648 bytes

Database mounted.

ORA-00313: open failed for members of log group 3 of thread 1

ORA-00312: online log 3 thread 1: ‘C:ORACLEORADATATEST1REDO03.LOG’

Database in Mounted Stage.

Now check the status of above mentioned redo log. It must be INACTIVE .. according to our scenario.

SQL> select l.status,lf.member from v$log l,v$logfile lf where l.group#=lf.group#;

STATUS MEMBER

————————————-

CURRENT C:ORACLEORADATATEST1REDO01.LOG

INACTIVE C:ORACLEORADATATEST1REDO02.LOG

INACTIVE C:ORACLEORADATATEST1REDO03.LOG

NOTE: Assumption is that there is least 3 redo log group in order to do the following.

SQL> alter database drop logfile group 3;

Database altered.

SQL> alter database open;

Database altered.

SQL> select group#, thread#,bytes, members from v$log;

GROUP# THREAD# BYTES MEMBERS

———- ———- ———- ———-

1 1 10485760 1

2 1 10485760 1

SQL> select member from v$logfile;

MEMBER

——————————————————————————–

C:ORACLEORADATATEST1REDO01.LOG

C:ORACLEORADATATEST1REDO02.LOG

SQL> alter database add logfile group 3 (‘C:ORACLEoradataTEST1REDO03.log’) size 10M;

Database altered.

SQL> select member from v$logfile;

MEMBER

——————————————————————————–

C:ORACLEORADATATEST1REDO01.LOG

C:ORACLEORADATATEST1REDO02.LOG

C:ORACLEORADATATEST1REDO03.LOG

SQL>

· CASE II – If the INACTIVE REDO log is lost during Database Open.

Database will automatically SHUTDOWN the very moment when the log switch happens onto that datafile which is lost. Then During STARTUP you will face the same error as seen in above CASE 1 of Scenario 1 … hence follow the same steps.

2. Loss of Current Online Redo Log Group – INCOMPLETE RECOVERY

SQL> startup

ORACLE instance started.

Total System Global Area 135338868 bytes

Fixed Size 453492 bytes

Variable Size 109051904 bytes

Database Buffers 25165824 bytes

Redo Buffers 667648 bytes

Database mounted.

ORA-00313: open failed for members of log group 1 of thread 1

ORA-00312: online log 1 thread 1: ‘C:ORACLEORADATATEST1REDO01.LOG’

Database is in Mounted Stage.

SQL> alter database drop logfile group 1;

alter database drop logfile group 1

ERROR at line 1:

ORA-01623: log 1 is current log for thread 1 – cannot drop

ORA-00312: online log 1 thread 1: ‘C:ORACLEORADATATEST1REDO01.LOG’

SQL> select group#, status, sequence# from v$log;

GROUP# STATUS SEQUENCE#

———- —————- ———-

1 CURRENT 47

2 INACTIVE 45

3 INACTIVE 46

SQL> recover automatic database until cancel; ————– Incomplete Recovery and Apply Archives If Needed.

Media recovery complete.

SQL> alter database open resetlogs;

Database altered.

SQL> select l.status,lf.member from v$log l,v$logfile lf where l.group#=lf.group#;

STATUS MEMBER

——————————————————————————–

CURRENT C:ORACLEORADATATEST1REDO01.LOG ———————-automatically created.

INACTIVE C:ORACLEORADATATEST1REDO02.LOG

INACTIVE C:ORACLEORADATATEST1REDO03.LOG

SQL>

A2Z of Items to be monitored in an Oracle Server

Sumit Singh Chadha — Mon, 03 Nov 2008 18:07:58 +0000

1. CPU Usage

2. I/O Contention

3. Free Memory Availaibility

4. Logs – alert.log,listener.log

5. Tablespace used space

6. Objects reaching MaxExtents

7. Users with DBA and SYSDBA priviliges

8. Disk Space Availaibility ( df –k )

9. Archive Mount Points Space Usage

10. ORACLE_HOME mount point usage

11. All mount points monitoring

12. Listener availaibility

13. OS Process consuming MAX CPU/IO

14. Connectivity using sqlplus – to check for maximum processes reached

15. DB Availaibility ( smon , pmon )

16. Dump files ( cdump , udump )

17. Memory Hit Ratios ( Shared Pool , DB Buffer Cache )

18. Backup logs ( exp , hot , cold , RMAN )

19. Standby DB ( running behind by how many logs ? )

20. Invalid Objects

21. Index Usage

22. Indexes which needs rebuild ( CF,BLEVEL and indexes which are bigger than theor parents table)

23. DB Audit – Basic

24. Locked Users

25. DB Size

26. Temporary Tablespace Usage

27. Undo Tablespace Usage

28. Datafile File I/O

29. A WEB PAGE – to display connectivity errors for all databases.

30. redo log sizing advisor in Oracle10g

31. Chained-Rows in tables increases I/O on datafiles , decrease chained rows by rebuilding objects or by modifying PCTFREE,PCTUSED parameter

32. Identifying files on which maximum I/O is occuring and then identifying objects present in them , and move them in tablespaces which have less I/O

33. OEMAgent Monitoring

34. Instance Availability

35. SMON,PMON processes

36. Capacity Planning

A2Z of Oracle Redo Logs

Sumit Singh Chadha — Mon, 03 Nov 2008 17:56:52 +0000

In this article we shall learn the following :-

1. What are redo logs?

2. What are redo logs used for ?

3. How to manage redo logs ?

4. How to determine the optimized size of redo logs ?

5. How does redo log size affect database performance ?