Flashback Technology

Dear All,
I have oracle 11g R2 32 bit version on windows 2003 R2 server. This is my testing database. My db size is 152gb and it is in archivelog mode with Flashback off.
I want to enable flashback in my testing enviornment.
Can any one clear my below doubts ...
1. What is the advantage and disadvantage of enabling Flashback ?
2. What are the verious criteria to define Flashback recover area size ?
2. What should be the flashback retention time ?
3. How Flashback technology really works in details ?
Thanks and Regards,
Vikash Chauradia (junior DBA)

1.) RMAN supports binary compression of backup sets, where the backup set contents are compressed before being written to disk using a compression algorithm tuned for compression of datafiles and archived log files. But with Image copy no compression is done.
•A backup set never contains empty blocks. As RMAN passes through the datafiles, it simply skips blocks that have never been used. But image copy contains empty blocks. This means that backups of datafiles as backup sets are generally smaller than image copy backups and take less time to write.
•Incremental backups can't be performed with Image copy but incremental backups can be taken over backup sets.
•RMAN can take backup of backup sets directly to tape, if you have installed the RMAN drivers for your tape library.But RMAN can't take backup of image copies directly to tape.
•Both Image copy and backup sets can be restored from RMAN. From Operating System Backup sets can't be generated or restored.
•RMAN will check the contents for corruption for both Image copy and backupsets but native operating-system file copy utilities cannot check corruption while taking backup of Image copy.
2.) it is not advisable to use the flashback area for backup restoration. The backup size is not fixed for each day. it's depend on the production of that particular days. In my case some day the backup of 25GB and very next day it goes to 55GB and also in increase the no. of archives also increases which again leads to increase in size of backup (if specifying archive in backup)
Hope this may help you :)
--neeraj

Similar Messages

Using Flashback Technology in Application

Hi all,
Can I use flashback in application, especially DBMS_FLASHBACK.TRANSACTION_BACKOUT. I import some information (from files) in my database and after that I want to revert that transaction(delete imported data). I did some test I took xid of the transaction from v$transaction and then executed DBMS_FLASHBACK.TRANSACTION_BACKOUT with that XID for parameter. Everything is fine but that time there was only one transaction, when there are many transaction how can I get the exact XID. I can use dbms_transaction.local_transaction_id to get information for transaction which is running. And when i tried to use flashback that way a deadlock occur and db killed the other transaction.
Thanks!

Is your problem that you cannot identify which single transaction to backout? If so, you can use flashback queries (projecting pseudo-columns such as VERSIONS_STARTTIME, VERSIONS_ENDTIME, and VERSIONS_XID) to find it. But be quick, or you'll get an ora-1555.

Problem with SPACE_RECLAIMABLE in Oracle Flashback

Hi All,
I have oracle 11.2.0.3 version running. I have some queries.
Recently I am learning about flashback technology.
What my issue is that the SPACE_RECLAIMABLE column always shows 0 although there is enough space in the flashback area.
Snapshot is as below.
SQL> select * from v$recovery_file_dest;
NAME SPACE_LIMIT SPACE_USED SPACE_RECLAIMABLE NUMBER_OF_FILES
C:\app\mudassar\fast_recovery_area 4353687552 104857600 0 2
I am not able to understand why? Where is the issue?
As per my understanding this should show the space that is free..
Please guide me on same.

822922 wrote:
Hi All,
I have oracle 11.2.0.3 version running. I have some queries.
Recently I am learning about flashback technology.
What my issue is that the SPACE_RECLAIMABLE column always shows 0 although there is enough space in the flashback area.
Snapshot is as below.
SQL> select * from v$recovery_file_dest;
NAME SPACE_LIMIT SPACE_USED SPACE_RECLAIMABLE NUMBER_OF_FILES
C:\app\mudassar\fast_recovery_area 4353687552 104857600 0 2
I am not able to understand why? Where is the issue?
As per my understanding this should show the space that is free..
Please guide me on same.http://docs.oracle.com/cd/E11882_01/server.112/e25513/dynviews_2125.htm#REFRN30304
{code}
SPACE_RECLAIMABLE NUMBER Total amount of disk space (in bytes) that can be created by deleting obsolete, redundant, and other low priority files from the fast recovery area
{code}
and probably
http://docs.oracle.com/cd/E11882_01/backup.112/e10642/rcmmaint.htm#BRADV89614
It does not show the space that is free, it shows the space that COULD BE freed if you removed files (see the list of possible files above) from the FRA.
Cheers,

Flashback table after shrink

Situation:
we deleted all rows from table, then alter table <> shrink space, that worked without any errors.
Now we decided to flasback that table to a timestamp before delete happend and of course before shrink too.
Flashback table <> to timestamp....... ended without any errors messages.
BUT only a few rows are now in table. Timestamp definitly has been correctly set to a point before delete happend:
WHAT MISTAKE DID WE MAKE??????
I NEED not to know how to get those rows back i only want to know if anyone has a clue why flashback didn't work correctly.
Tanks to all
Joachim Kreimes

There are two table Flashback technologies in Oracle:cFlashback to SCN or Timestamp is Flashback Table using Undo. Flashback to before drop uses the Recyclebin.
The following DDL operations change the structure of a table, so that you cannot subsequently use the TO SCN or TO TIMESTAMP clause to flash the table back to a time preceding the operation: upgrading, moving, or truncating a table; adding a constraint to a table, adding a table to a cluster; modifying or dropping a column; adding, dropping, merging, splitting, coalescing, or truncating a partition or subpartition (with the exception of adding a range partition).

Flashback VERSIONS_XID

Hi,
I found the following question and do not understand the answer:
You want to use the Flashback Transaction Query to identify the SQL needed to reverse a transaction in the HR. EMPLOYEES table. Where can you find out the value of the transaction ID column XID to use when you query FLASHBACK_TRANSACTION_QUERY?
a) from the VERSIONS_XID column of HR.EMPLOYEES
b) from LogMiner
c) from XID column of HR.EMPLOYEES
d) from the VERSIONS_XID column of FLASHBACK_VERSION_QUERY
Answer A
Every table has the pseudo-column VERSIONS_XID that you can query for a transaction ID of a past transaction with the AS OF clause.
D is incorrect because there is no such column VERSIONS_XID of the FLASHBACK_VERSION_QUERY; you need to have the XID or SCN before querying FLASHBACK_VERSION_QUERY and retreive the SQL to reverse the transaction.
I think the answer is D and not A. A is a flashback query that does not show the VERSIONS_XID column. Flashback version query using VERSIONS BETWEEN shows the VERSION_XID column. Can somebody confirm this or explain please?
Thanks.

Dude wrote:
Aman wrote:
D is anyways incorrect since there is no such table or view with the name flashback_version_query.Are you saying this because of the underlines in the name: I suggest that this is a typo and FLASHBACK_VERSION_QUERY should read FLASHBACK VERSION QUERY.No, I am saying because there is no such view at all, underlines being there or not there has nothing to do with it. Please see,
SQL> desc flashback_version_query
ERROR:
ORA-04043: object flashback_version_query does not exist
SQL> desc flashback_versions_query
ERROR:
ORA-04043: object flashback_versions_query does not exist
SQL> desc flashback_transaction_query
Name
XID
START_SCN
START_TIMESTAMP
COMMIT_SCN
COMMIT_TIMESTAMP
LOGON_USER
UNDO_CHANGE#
OPERATION
TABLE_NAME
TABLE_OWNER
ROW_ID
UNDO_SQL
SQL> select * from V$version;
BANNER
Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - Production
PL/SQL Release 11.2.0.1.0 - Production
CORE    11.2.0.1.0      Production
TNS for 32-bit Windows: Version 11.2.0.1.0 - Production
NLSRTL Version 11.2.0.1.0 - Production
SQL>This should be sufficient to prove that there is no such view with the name Flashback_version_query . Its a term NOT a view's name by itself. Please see,
http://download.oracle.com/docs/cd/E11882_01/server.112/e17157/unplanned.htm#sthref167
Whereas, the flashback_transaction_query is a documented view.
http://download.oracle.com/docs/cd/E11882_01/server.112/e17110/statviews_5120.htm#REFRN29086
I hope the above mentioned points must remove the confusion between the two. If not, we need to sort this out before going further. PLease confirm this. If you do agree to it, let's continue.
>
That's possible from the pseudo column versions_xid which appears if one uses the Version Query. So the correct answer is A. Nope , that's a psedo column in the query and since the view with the name flasback_version_query( without underlines too) is NOT there, we are talking about two different things. The pseudo column versions_xid is an actual column BUT with the name XID in the FLashback_transaction_query . BIG DIFFERENCE!! . So not the same but if you are still thinking that they are, please read the above mentioned point which you must agree before we discuss this current point.
Than D must be correct, getting the VERSIONS_XID column of FLASHBACK VERSION QUERY. Answer A does not say anything about using flashback.
It doesn't need to. That's why it's a trick question.
a) from the VERSIONS_XID column of HR.EMPLOYEES
d) from the VERSIONS_XID column of FLASHBACK_VERSION_QUERY
I think the given explanation why A is correct, saying that every table provides Version XID using AS OF clause is incorrect, because it is normal flashback query.
are you sure about this statement Dude since it's incorrect! PLease see,
SQL> select * from V$version;
BANNER
Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - Production
PL/SQL Release 11.2.0.1.0 - Production
CORE    11.2.0.1.0      Production
TNS for 32-bit Windows: Version 11.2.0.1.0 - Production
NLSRTL Version 11.2.0.1.0 - Production
SQL> conn aman/aman
ERROR:
ORA-28002: the password will expire within 7 days
Connected.
SQL> create table test_test as select * from scott.emp;
Table created.
SQL> select current_scn from V$database;
CURRENT_SCN
    2628878
SQL> select current_scn from V$database;
CURRENT_SCN
    2628881
SQL> select versions_xid from test_test as of scn 2628878;
select versions_xid from test_test as of scn 2628878
ERROR at line 1:
ORA-00904: "VERSIONS_XID": invalid identifier
SQL> select versions_xid from test_test versions between scn minvalue and maxvalue;'
2
SQL> select versions_xid from test_test versions between scn minvalue and maxvalue;
VERSIONS_XID
14 rows selected.
SQL>Saw the difference? There is no versions_xid column returned with the vanilla Flashback query . When added Flashback version query, then only its becoming visible. So your assumption is incorrect completely.
Flashback version query is using VERSIONS BETWEEN. Anyway, answer A does not say anything about using Flashback technology at all.
PhoenixBai wrote:
You don`t read careful enough. I have told you where that '00200030000002D' come from, from the first sql I listed:Yes, sorry, but then again, VERSIONS BETWEEN is flashback version query. Answer A does not mention any Flashback operation.It doesn't need to as I said already. That's what the trick in the question. There won't be any fun if it would be a straight-forward question.
Sorry for being persistent, but I cannot see why A is right and D is wrong.
IF you are still going to be persistent, I am sorry to say that you have got one question of yours wrong and it would be purely your fault :) .
HTH
Aman....

Flashback version and transaction

Hi
Does flashback versions and flashback transactions query use the undo data.How long can we use flashback versions query..

Sekar_BLUE4EVER wrote:
Hi
Does flashback versions and flashback transactions query use the undo data.How long can we use flashback versions query..Yes they both use UNDO data. You need to specify UNDO_RETENTION
Check the following link:
http://www.databasejournal.com/features/oracle/article.php/3819031/Is-Your-UNDO-Tablespace-Prepared-for-Oracles-Flashback-Technology.htm
Kamran Agayev A.
Oracle ACE
My Oracle Video Tutorials - http://kamranagayev.wordpress.com/oracle-video-tutorials/

Oracle's Flashback Technolgy

Hi,
Can any one kindly explain how the Oracle's Flashback Technology works? I mean OFT depends on Automatic Undo Managemet but how exactly it works? Whats the architecture?
Any good link or book name that explains the OFT in detail will be very helpfull.
Actually this was a Interview Question which i failed to answer. I just said that its dependent on Automatic Undo Management.. but they needed a more detailed answer.
Kindly explain.
Thanks in Advance.
SID

A lot of times, what is asked in the interview and what is expected by the interviewer, these are far away from what is there. If someone failed you saying that undo is used for Flashback, I would actually have asked what else he/she wants to know beyond this? And I won't suggest that you should spend time and energy thinking that you knwo somewhat lesser just because some one said to you that he is not happy from your answer. You should have asked what's the answer he is looking for then?
In 10g, except for Flashback database, rest of the entire stuff is based on the Undo data only. That's it! In 11g, there are changes to this but that needs to be told that the person who is asking is willing to know about 11g's enhancements.
HTH
Aman....

Flashback transaction

HI,
I have deleted one row from a table and corresponding query from flashback_transaction_query gives following output:
SQL> select start_timestamp,operation,commit_timestamp from flashback_transaction_query where xid=hextoraw('07000E0023020000');
START_TIMESTAMP OPERATION COMMIT_TIMESTAMP
20-feb-2006 13:07:37 DELETE 20-feb-2006 13:07:49
20-feb-2006 13:07:37 BEGIN 20-feb-2006 13:07:49
It also shows operation BEGIN in specified interval. Whats its significance as only delete operation takes place.
Neeraj

There are multiple demos of Flashback technology demonstrating what they do in Morgan's Library at www.psoug.org.
The impact of undo_retention is important in 10g though it is certainly no guarantee. In 11g use Flashback Archive to create a more-or-less permanent storage facility for undo information and then undo retention is meaningless with regard to Flashback Tx.

Flashback table not responding

hi,
i am using oracle 10g R2 on linux X86. i have flashback feature set to true. one of my table was accidently truncated.
now i want it back.other tables are brought back with flashback technology.
but this one is generating error that "the table definition has been changed" i dont made any changes to table definition.
what might be the issue? even though i have backup,but still would like to know,and recover it with the help of flashback.
flashback retention target has been set to 900. and table was droped much before that.
plz help
thanks and regards
VD

Vikrant,
Why would I mind explaining?
Anyways, see below a small code.
SQL> create table aman_t (a number);
Table created.
SQL> desc dba_extents;
Name                                      Null?    Type
OWNER                                              VARCHAR2(30)
SEGMENT_NAME                                       VARCHAR2(81)
PARTITION_NAME                                     VARCHAR2(30)
SEGMENT_TYPE                                       VARCHAR2(18)
TABLESPACE_NAME                                    VARCHAR2(30)
EXTENT_ID                                          NUMBER
FILE_ID                                            NUMBER
BLOCK_ID                                           NUMBER
BYTES                                              NUMBER
BLOCKS                                             NUMBER
RELATIVE_FNO                                       NUMBER
SQL> select segment_name,extent_id,blocks from dba_extents where segment_name='AMAN_T';
SEGMENT_NAME
EXTENT_ID     BLOCKS
AMAN_T
         0          8
SQL> begin
2 for i in 1..10000 loop
3 insert into aman_t values(i);
4 end loop;
5 commit;
6 end;
7 /
PL/SQL procedure successfully completed.
SQL> select segment_name,extent_id,blocks from dba_extents where segment_name='AMAN_T';
SEGMENT_NAME
EXTENT_ID     BLOCKS
AMAN_T
         0          8
AMAN_T
         1          8
AMAN_T
         2          8
SQL> commit;
Commit complete.
SQL> exec dbms_stats.gather_table_stats(user,'AMAN_T');
PL/SQL procedure successfully completed.
SQL> select segment_name,extent_id,blocks from dba_extents where segment_name='AMAN_T';
SEGMENT_NAME
EXTENT_ID     BLOCKS
AMAN_T
         0          8
AMAN_T
         1          8
AMAN_T
         2          8
SQL> delete from aman_t;
10000 rows deleted.
SQL> exec dbms_stats.gather_table_stats(user,'AMAN_T');
PL/SQL procedure successfully completed.
SQL> select segment_name,extent_id,blocks from dba_extents where segment_name='AMAN_T';
SEGMENT_NAME
EXTENT_ID     BLOCKS
AMAN_T
         0          8
AMAN_T
         1          8
AMAN_T
         2          8
SQL> truncate table aman_t;
Table truncated.
SQL> exec dbms_stats.gather_table_stats(user,'AMAN_T');
PL/SQL procedure successfully completed.
SQL> select segment_name,extent_id,blocks from dba_extents where segment_name='AMAN_T';
SEGMENT_NAME
EXTENT_ID     BLOCKS
AMAN_T
         0          8
SQL>You should be able to see that when I issued a delete command, the number of allocated extents are the same.Which does mean that though the blocks are empty but the HWM is still pointing towards those blocks.I gathered stats just to ensure that you won't come back and say that aafter gathering them,things would be different.
When I gave truncate, you can see that oracle came back to the initially allocated first extent only. This is table definition change and this did happen with my last demo and with your original scenerio as well.
Now just to confuse you a little more, even gathering of stats would be called as definition change. See below,
SQL> drop table aman_t purge;
Table dropped.
SQL> create table amna_t( a char);
Table created.
SQL> exec dbms_stats.gather_table_stats(user,'AMNA_T');
PL/SQL procedure successfully completed.
SQL> alter table amna_t enable row movement;
Table altered.
SQL> flashback table amna_T to timestamp(sysdate - 1/24/60);
flashback table amna_T to timestamp(sysdate - 1/24/60)
ERROR at line 1:
ORA-01466: unable to read data - table definition has changed
SQL>So I hope you should be clear now that you can't get back the data with Flashback as this relies over the Undo data and can only get back the logical changes , not the structural changes over the object.
HTH
Aman....

Flashback after rman reccovery???

Hi all,
I have a scenario,
I have taken a rman backup yesterday at 7:30PM. but one of my developer have deleted data from a table by 5:30 PM. We dont have the backup of the table before it was deleted.
Now we recovered the database with the backup taken yesterday and found out that the data was missing in the table.
The database is in archive log mode.
My question is:
1. Can the data from the particular table can be recovered.
2. Will flashback works with this recovered database..
Please help!!!!!!!!11

The table was truncated or deleted? If it was deleted then what is your undo retention? You can use flashback technology but it is depended on you UNDO TS size and undo retention.
Talip Hakan Ozturk
http://taliphakanozturken.wordpress.com/

Flashback Functionality

DB:11.2.0.3
I want to test the flashback functionality. I have a table of size 1.5 GB and my flashback area is of size 1GB. If i drop the table can i restore it from flashback.

user13549752 wrote:
DB:11.2.0.3
I want to test the flashback functionality. I have a table of size 1.5 GB and my flashback area is of size 1GB. If i drop the table can i restore it from flashback.Flashback is a concept actually and it has got many things under it which are applicable to different levels of issues. The table drop is covered with Recyclebin concept under Flashback technology. I believe you should spend some time reading about Flashback from docs at http://tahiti.oracle.com .
Aman....

Flashback compatibility

Hi guys,
having EBS rel. 12, the flashback technologies rdbms is compatibile/certified with it?
Can i use flashback area and flashback feature for restore database object (tables, rows, etc..) in ebs?? or there is some misleading from application layer to DB ?
I've not found any documents that explain flashback on EBS.
thanks very much!
Andrew

Use of the Flashback database feature is supported with the E-Business Suite. The base Oracle database documentation applies to E-Business Suite, so there's no Apps-specific documentation for using this feature.
Maximum Availability Architectures & the E-Business Suite
http://blogs.oracle.com/schan/discuss/msgReader$911

EMERGENCY: Need to flashback table, how to find SCN for a time before update happened?

Hi all,
I've got a new database 11G, I've not used flashback before, but my retention time is a day...I have a time that the developer did a massive update to a table to corrupt it.
How do I find the SCN for that time so I can attempt to flashback that table?
Thank you,
cayenne

Thank you..I also found this works:
SQL> select timestamp_to_scn(to_timestamp('20140103152000','YYYYMMDDHH24MISS')) scn from dual;
       SCN
98344246
Well that might NOT work all of the time. But that is just what Oracle does when you give it a timestamp to flashback to: it converts the timestamp to an SCN and then restores data based on that SCN.
See Flashback Table in the SQL Language doc
http://docs.oracle.com/cd/B28359_01/server.111/b28286/statements_9012.htm
TO TIMESTAMP Clause
Specify a timestamp value corresponding to the point in time to which you want to return the table. The expr must evaluate to a valid timestamp in the past. The table will be flashed back to a time within approximately 3 seconds of the specified timestamp.
That 'approximately 3 seconds' accuracy is due to that conversion to SCN - Oracle uses its internal table.
SCN is accurate if you know it but you usually don't.
Read, and heed, these warnings in the advanced app dev guide
http://docs.oracle.com/cd/B28359_01/appdev.111/b28424/adfns_flashback.htm
Guidelines for Oracle Flashback Query
If a possible 3-second error (maximum) is important to Oracle Flashback Query in your application, use an SCN instead of a timestamp. See General Guidelines for Oracle Flashback Technology.
General Guidelines for Oracle Flashback Table
To query past data at a precise time, use an SCN. If you use a timestamp, the actual time queried might be up to 3 seconds earlier than the time you specify. Oracle Database uses SCNs internally and maps them to timestamps at a granularity of 3 seconds.
     For example, suppose that the SCN values 1000 and 1005 are mapped to the timestamps 8:41 AM and 8:46 AM, respectively. A query for a time between      8:41:00 and 8:45:59 AM is mapped to SCN 1000; an Oracle Flashback Query for 8:46 AM is mapped to SCN 1005.
     Due to this time-to-SCN mapping, if you specify a time that is slightly after a DDL operation (such as a table creation) Oracle Database might use an SCN      that is just before the DDL operation, causing error ORA-1466.

Worth to use Flashback and useful?

I'm new in oracle system design and very confused.
In newer version of Oracle, flashback technology was introduced. If my user won't call DBA to rollback some data suddenly, what is the purpose of it?
Even if a user want to flashback some data, there may be many data dependence or data integrity problems.
Also, if the db_recovery_file_dest_size is not enough within db_flashback_retention_target somehow, there may be error "ORA-38700: Limit of %s flashback database logs has been exceeded" which affects the daily operation.
Unless the size of UNDO and REDO Logs are enough, it is not worth to maintain the flashback feature, isn't it?
Thanks in advance!

Anothony,
Flashback and Flashback database are two different things , made to recover from two different kind of erros. Its indeed correct to say that Flashback is related to Undo and there should be a sufficient size for the Undo to be available. But assume a situation where a logical change, for example, all teh salaries have been made to zero, will your user would wait for 4 days to come to know about it? I guess not. The default size of Undo retention, on which Flashback is based primarily , is for 900 seconds(15 minutes). If you need more bigger time frame than that, you can always go for a larget sized Undo space.
The retention target that you have mentioned for Flashback, is NOT for the statndard Falshback but for the Flashback Database technology, a completely diffetent thing to recover or rewind the entire database which have undergone massive logical corruptions. The default for this is False that means the database is not in the Flashback mode by default. And this setting doesn't rely upon the setting of teh undo retention as a completely different process writes the records to the Flb files of the Flashback log and maintains it for the retention period that you would specify in the target parameter. This is again set to a high and almost suffificient value, 1 day, which should be enough for a db. Redo logs won't take part in the Flashback technology.
The only feaure that you would enable explicitly is Flashback Database, rest all is by default maintained by Oracle implicitly. I don't see any good in going back to RBS in the current era. And if you are using AUM, than you are going to have Flashback technology already on for you. Yeah, you use it or not, that depends on you and on your users.
HTH
Aman....

Estimate of Flashback logs to expect for my database

Hi all,
Please I need to know (roughly) the size of flahback logs to expect for my database.
My database is about 500G in size, grows at about 1% per month and I hope to keep flashback logs for 48 hrs.
If you currently use the flashback technology, let me know your database size, how many hours of flashback logs you keep and the size of your logs. If I get 2 or 3 responses, then I'll be able to make an intelligent guess for what my database flahback log size might be.
Regards
baffy

The value of the DB_FLASHBACK_RETENTION_TARGET parameter (1440
minutes in our example) determines how much flashback data the database should
retain in the form of flashback database logs in the flash recovery area. In order to
estimate the space you need to add to your flash recovery area for accommodating
the flashback database logs, first run the database for a while with the flashback
database feature turned on. Then run the following query:
SQL> select estimated_flashback_size, retention_target,
flashback_size from v$flashback_database_log;
ESTIMATED_FLASHBACK_SIZE RETENTION_TARGET FLASHBACK_SIZE
126418944 1440 152600576

Flashback Technology

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