Data Recovery Advisor - Oracle 11G R2

Backup and Recovery

Advice on data recovery, parallel backup of the same file, virtual catalogs for security, duplicate database from backup, undrop a tablespace, and secure backup to the cloud are just a few of the new gems available from RMAN in Oracle Database 11g.

Reference:- www.oracle.com

Data Recovery Advisor

Consider the error shown below:

SQL> conn scott/tiger
Connected.
SQL> create table t (col1 number);
create table t (col1 number)
*
ERROR at line 1:
ORA-01116: error in opening database file 4
ORA-01110: data file 4: '/home/oracle/oradata/PRODB3/users01.dbf'
ORA-27041: unable to open file
Linux Error: 2: No such file or directory
Additional information: 3

Does it look familiar? Regardless of your experience as a DBA, you probably have seen this message more than once. This error occurs because the datafile in question is not available—it could be corrupt or perhaps someone removed the file while the database was running. In any case, you need to take some proactive action before the problem has a more widespread impact.

In Oracle Database 11g, the new Data Recovery Advisor makes this operation much easier. The advisor comes in two flavors: command line mode and as a screen in Oracle Enterprise Manager Database Control. Each flavor has its advantages for a given specific situation. For instance, the former option comes in handy when you want to automate the identification of such files via shell scripting and schedule recovery through a utility such as cron or at. The latter route is helpful for novice DBAs who might want the assurance of a GUI that guides them through the process. I'll describe both here.

Command Line Option

The command line option is executed through RMAN. First, start the RMAN process and connect to the target.

 
$ rman target=/
 
Recovery Manager: Release 11.1.0.5.0 - Beta on Sun Jul 15 19:43:45 2007
 
Copyright (c) 1982, 2007, Oracle.  All rights reserved.
 
connected to target database: PRODB3 (DBID=3132722606)

Assuming that some error has occurred, you want to find out what happened. The list failure command tells you that in a jiffy. 

RMAN> list failure;

If there is no error, this command will come back with the message:

no failures found that match specification

If there is an error, a more explanatory message will follow:

using target database control file instead of recovery catalog
List of Database Failures
=========================
 
Failure ID Priority Status    Time Detected Summary
----------      --------     ---------     -------------       -------
142        HIGH     OPEN      15-JUL-07     One or more non-system datafiles are missing

This message shows that some datafiles are missing. As the datafiles belong to a tablespace other than SYSTEM, the database stays up with that tablespace being offline. This error is fairly critical, so the priority is set to HIGH. Each failure gets a Failure ID, which makes it easier to identify and address individual failures. For instance you can issue the following command to get the details of Failure 142.

RMAN> list failure 142 detail;

This command will show you the exact cause of the error.

Now comes the fun part: How do you rectify the error? Seasoned DBAs will probably ace this without further help but novice DBAs (and even experienced but tired ones) will welcome some guidance here. They can turn to Data Recovery Advisor for assistance:

RMAN> advise failure;

It responds with a detailed explanation of the error and how to correct it:

List of Database Failures
=========================
 
Failure ID Priority Status    Time Detected Summary
----------      --------     ---------     -------------       -------
142        HIGH     OPEN      15-JUL-07     One or more non-system datafiles are missing
 
analyzing automatic repair options; this may take some time
using channel ORA_DISK_1
analyzing automatic repair options complete
 
Mandatory Manual Actions
========================
no manual actions available
 
Optional Manual Actions
=======================
1. If file /home/oracle/oradata/PRODB3/users01.dbf was unintentionally renamed or moved, restore it
 
Automated Repair Options
========================
Option Repair Description
------ ------------------
1      Restore and recover datafile 4  
  Strategy: The repair includes complete media recovery with no data loss
  Repair script: /home/oracle/app/diag/rdbms/prodb3/PRODB3/hm/reco_3162589478.hm

This output has several important parts. First, the advisor analyzes the error. In this case, it's pretty obvious: the datafile is missing. Next, it suggests a strategy. In this case, this is fairly simple as well: restore and recover the file. (Please note that I have deliberately chosen a simple example to focus the attention on the usage of the tool, not to discuss the many cases where the database could fail and how they can be recovered. The dynamic performance view V$IR_MANUAL_CHECKLIST also shows this information.)

However, the most useful task Data Recovery Advisor does is shown in the very last line: it generates a script that can be used to repair the datafile or resolve the issue. The script does all the work; you don't have to write a single line of code.

Sometimes the advisor doesn't have all the information it needs. For instance, in this case, it does not know if someone moved the file to a different location or renamed it. In that case, it advises to move the file back to the original location and name (under Optional Manual Actions).

OK, so the script is prepared for you. Are you ready to execute it? I don't know about you, but I would verify what the script actually does first. So, I issue the following command to "preview" the actions the repair task will execute:

RMAN> repair failure preview;
 
Strategy: The repair includes complete media recovery with no data loss
Repair script: /home/oracle/app/diag/rdbms/prodb3/PRODB3/hm/reco_741461097.hm
 
contents of repair script:
   # restore and recover datafile
   sql 'alter database datafile 4 offline';
   restore datafile 4;
   recover datafile 4;
   sql 'alter database datafile 4 online';

This is good; the repair seems to be doing the same thing I would have done myself using RMAN. Now I can execute the actual repair by issuing:

RMAN> repair failure;
 
Strategy: The repair includes complete media recovery with no data loss
Repair script: /home/oracle/app/diag/rdbms/prodb3/PRODB3/hm/reco_3162589478.hm
 
contents of repair script:
   # restore and recover datafile
   sql 'alter database datafile 4 offline';
   restore datafile 4;
   recover datafile 4;
   sql 'alter database datafile 4 online';
 
Do you really want to execute the above repair (enter YES or NO)?

Assuming I'm OK, I answer YES and the action goes on:

executing repair script
 
sql statement: alter database datafile 4 offline
 
Starting restore at 15-JUL-07
using channel ORA_DISK_1
 
channel ORA_DISK_1: restoring datafile 00004
input datafile copy RECID=5 STAMP=628025835 file name=/home/oracle/flasharea/PRODB3/datafile/o1_mf_users_39ocxbv3_.dbf
destination for restore of datafile 00004: /home/oracle/oradata/PRODB3/users01.dbf
channel ORA_DISK_1: copied datafile copy of datafile 00004
output file name=/home/oracle/oradata/PRODB3/users01.dbf RECID=0 STAMP=0
Finished restore at 15-JUL-07
 
Starting recover at 15-JUL-07
using channel ORA_DISK_1
 
starting media recovery
 
archived log for thread 1 with sequence 51 is already on disk as file /home/oracle/flasharea/PRODB3/archivelog/2007_07_15/o1_mf_1_51_39ocxxdw_.arc
...  
                              
and so on ...
name=/home/oracle/flasharea/PRODB3/archivelog/2007_07_15/o1_mf_1_55_39ocy9ox_.arc thread=1 sequence=55
media recovery complete, elapsed time: 00:00:01
Finished recover at 15-JUL-07
 
sql statement: alter database datafile 4 online
repair failure complete
 
RMAN>
                            

Note how RMAN prompts you before attempting to repair. In a scripting case, you may not want to do that; rather, you would want to just go ahead and repair it without an additional prompt. In such a case, just use repair failure noprompt at the RMAN prompt.

 

Proactive Health Checks

It helps you sleep better at night knowing that the database is healthy and has no bad blocks. But how can you ensure that? Bad blocks show themselves only when they are accessed so you want to identify them early and hopefully repair them using simple commands before the users get an error.

The tool dbverify can do the job but it might be a little inconvenient to use because it requires writing a script file contaning all datafiles and a lot of parameters. The output also needs scanning and interpretation. In Oracle Database 11g, a new command in RMAN,VALIDATE DATABASE, makes this operation trivial by checking database blocks for physical corruption. If corruption is detected, it logs into the Automatic Diagnostic Repository. RMAN then produces an output that is partially shown below:

RMAN> validate database;
 
Starting validate at 09-SEP-07
using target database control file instead of recovery catalog
allocated channel: ORA_DISK_1
channel ORA_DISK_1: SID=110 device type=DISK
channel ORA_DISK_1: starting validation of datafile
channel ORA_DISK_1: specifying datafile(s) for validation
input datafile file number=00002 name=/home/oracle/oradata/ODEL11/sysaux01.dbf
input datafile file number=00001 name=/home/oracle/oradata/ODEL11/system01.dbf
input datafile file number=00003 name=/home/oracle/oradata/ODEL11/undotbs01.dbf
input datafile file number=00004 name=/home/oracle/oradata/ODEL11/users01.dbf
channel ORA_DISK_1: validation complete, elapsed time: 00:02:18
List of Datafiles
=================
File Status Marked Corrupt Empty Blocks Blocks Examined High SCN
----   ------    --------------        ------------       ---------------        ----------
1    OK     0              12852        94720           5420717   
  File Name: /home/oracle/oradata/ODEL11/system01.dbf
  Block Type Blocks Failing Blocks Processed
  ---------- --------------          ----------------
  Data       0              65435           
  Index      0              11898           
  Other      0              4535            
 
File Status Marked Corrupt Empty Blocks Blocks Examined High SCN
----   ------    --------------        ------------ -     --------------         ----------
2    OK     0              30753        115848          5420730   
  File Name: /home/oracle/oradata/ODEL11/sysaux01.dbf
  Block Type Blocks Failing Blocks Processed
  ---------- --------------          ----------------
  Data       0              28042           
  Index      0              26924           
  Other      0              30129           
 
File Status Marked Corrupt Empty Blocks Blocks Examined High SCN
----   ------    --------------        ------------       ---------------        ----------
3    OK     0              5368         25600           5420730   
  File Name: /home/oracle/oradata/ODEL11/undotbs01.dbf
  Block Type Blocks Failing Blocks Processed
  ---------- --------------      ----------------
  Data       0              0               
  Index      0              0               
  Other      0              20232           
 
File Status Marked Corrupt Empty Blocks Blocks Examined High SCN
---- ------ -------------- ------------ --------------- ----------
4    OK     0              2569         12256           4910970   

...  
                              
<snipped> ...
                            

Otherwise, in case of a failure you will see on parts of the above output:

List of Datafiles
=================
File Status Marked Corrupt Empty Blocks Blocks Examined High SCN
----   ------    --------------        ------------       ---------------        ----------
7    FAILED 0              0            128             5556154   
  File Name: /home/oracle/oradata/ODEL11/test01.dbf
  Block Type Blocks Failing Blocks Processed
  ---------- --------------        ----------------
  Data       0              108             
  Index      0              0               
  Other      10             20              

You can also validate a specific tablespace:

RMAN> validate tablespace users;

Or, datafile:

RMAN> validate datafile 1;

Or, even a block in a datafile:

RMAN> validate datafile 4 block 56;

The VALIDATE command extends much beyond datafiles however. You can validate spfile, controlfilecopy, recovery files, Flash Recovery Area, and so on.