data recovery advisor

8/7/2019 Data Recovery Advisor

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Data Recovery AdvisorConsider the error shown below:

SQL> conn scott/tigerConnected.SQL> create table t (col1 number);create table t (col1 number)

*ERROR at line 1:ORA-01116: error in opening database file 4ORA-01110: data file 4: '/home/oracle/oradata/PRODB3/users01.dbf'ORA-27041: unable to open fileLinux Error: 2: No such file or directoryAdditional information: 3Does it look familiar? Regardless of your experience as a DBA, you probably have seen this message more than once. This erroroccurs because the datafile in question is not availableit could be corrupt or perhaps someone removed the file while thedatabase 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 givenspecific situation. For instance, the former option comes in handy when you want to automate the identification of such files viashell scripting and schedule recovery through a utility such as cron or at. The latter route is helpful for novice DBAs who mightwant the assurance of a GUI that guides them through the process. I'll describe both here.

Command Line OptionThe 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 2007Copyright (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 ajiffy.

RMAN> list failure;If there is no error, this command will come back with the message:

no failures found that match specificationIf there is an error, a more explanatory message will follow:

using target database control file instead of recovery catalogList of Database Failures=========================Failure ID Priority Status Time Detected Summary---------- -------- --------- ------------- -------142 HIGH OPEN 15-JUL-07 One or more non-systemdatafiles are missingThis 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 thedetails 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=========================


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Failure ID Priority Status Time Detected Summary---------- -------- --------- ------------- -------142 HIGH OPEN 15-JUL-07 One or more non-systemdatafiles are missinganalyzing automatic repair options; this may take some timeusing channel ORA_DISK_1analyzing automatic repair options completeMandatory Manual Actions========================no manual actions availableOptional Manual Actions=======================1. If file /home/oracle/oradata/PRODB3/users01.dbf was unintentionallyrenamed or moved, restore itAutomated Repair Options

========================Option Repair Description------ ------------------1 Restore and recover datafile 4Strategy: The repair includes complete media recovery with no data

lossRepair script:

/home/oracle/app/diag/rdbms/prodb3/PRODB3/hm/reco_3162589478.hmThis output has several important parts. First, the advisor analyzes the error. In this case, it's pretty obvious: the datafile ismissing. Next, it suggests a strategy. In this case, this is fairly simple as well: restore and recover the file. (Please note that I havedeliberately chosen a simple example to focus the attention on the usage of the tool, not to discuss the many cases where thedatabase could fail and how they can be recovered. The dynamic performance view V$IR_MANUAL_CHECKLIST also shows thisinformation.)However, the most useful task Data Recovery Advisor does is shown in the very last line: it generates a script that can be used torepair 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 thefile to a different location or renamed it. In that case, it advises to move the file back to the original location and name (underOptional 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 scriptactually 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 lossRepair script:/home/oracle/app/diag/rdbms/prodb3/PRODB3/hm/reco_741461097.hmcontents 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 actualrepair by issuing:

RMAN> repair failure;Strategy: The repair includes complete media recovery with no data loss


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Repair script:/home/oracle/app/diag/rdbms/prodb3/PRODB3/hm/reco_3162589478.hmcontents of repair script:

# restore and recover datafilesql '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 scriptsql statement: alter database datafile 4 offlineStarting restore at 15-JUL-07using channel ORA_DISK_1channel ORA_DISK_1: restoring datafile 00004

input datafile copy RECID=5 STAMP=628025835 filename=/home/oracle/flasharea

/PRODB3/datafile/o1_mf_users_39ocxbv3_.dbfdestination for restore of datafile 00004:/home/oracle/oradata/PRODB3/users01.dbfchannel ORA_DISK_1: copied datafile copy of datafile 00004output file name=/home/oracle/oradata/PRODB3/users01.dbf RECID=0 STAMP=0Finished restore at 15-JUL-07Starting recover at 15-JUL-07using channel ORA_DISK_1

starting media recoveryarchived log for thread 1 with sequence 51 is already on disk asfile /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_39o

cy9ox_.arc thread=1 sequence=55media recovery complete, elapsed time: 00:00:01Finished recover at 15-JUL-07sql statement: alter database datafile 4 onlinerepair failure completeRMAN>


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Note how RMAN prompts you before attempting to repair. In a scripting case, you may not want to do that; rather, you would wantto 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 ChecksIt helps you sleep better at night knowing that the database is healthy and has no bad blocks. But how can you ensure that? Badblocks show themselves only when they are accessed so you want to identify them early and hopefully repair them using simplecommands 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 alldatafiles and a lot of parameters. The output also needs scanning and interpretation. In Oracle Database 11g, a new command inRMAN, VALIDATE DATABASE, makes this operation trivial by checking database blocks for physical corruption. If corruption isdetected, 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-07using target database control file instead of recovery catalogallocated channel: ORA_DISK_1channel ORA_DISK_1: SID=110 device type=DISKchannel ORA_DISK_1: starting validation of datafilechannel ORA_DISK_1: specifying datafile(s) for validationinput datafile file number=00002name=/home/oracle/oradata/ODEL11/sysaux01.dbf

input datafile file number=00001name=/home/oracle/oradata/ODEL11/system01.dbfinput datafile file number=00003name=/home/oracle/oradata/ODEL11/undotbs01.dbfinput datafile file number=00004name=/home/oracle/oradata/ODEL11/users01.dbfchannel ORA_DISK_1: validation complete, elapsed time: 00:02:18List of Datafiles=================File Status Marked Corrupt Empty Blocks Blocks Examined High SCN---- ------ -------------- ------------ --------------- ----------1 OK 0 12852 94720 5420717File Name: /home/oracle/oradata/ODEL11/system01.dbf

Block Type Blocks Failing Blocks Processed---------- -------------- ----------------Data 0 65435Index 0 11898Other 0 4535

File Status Marked Corrupt Empty Blocks Blocks Examined High SCN---- ------ -------------- ------------ --------------- ----------2 OK 0 30753 115848 5420730File Name: /home/oracle/oradata/ODEL11/sysaux01.dbfBlock Type Blocks Failing Blocks Processed---------- -------------- ----------------Data 0 28042Index 0 26924

Other 0 30129

File Status Marked Corrupt Empty Blocks Blocks Examined High SCN---- ------ -------------- ------------ --------------- ----------3 OK 0 5368 25600 5420730File Name: /home/oracle/oradata/ODEL11/undotbs01.dbfBlock Type Blocks Failing Blocks Processed---------- -------------- ----------------Data 0 0


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Index 0 0Other 0 20232

File Status Marked Corrupt Empty Blocks Blocks Examined High SCN---- ------ -------------- ------------ --------------- ----------4 OK 0 2569 12256 4910970

...

...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 5556154File Name: /home/oracle/oradata/ODEL11/test01.dbfBlock Type Blocks Failing Blocks Processed---------- -------------- ----------------

Data 0 108Index 0 0Other 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, FlashRecovery Area, and so on.

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