Contents of flashback and undo ?

When Flashback logs are generated would UNDO also be filed ?
Would the contents of Flashback logs and Undo Logs be the same ?
I believe undo information is stored in SGA and then the Undo Logs.

When Flashback logs are generated would UNDO also be filed ?
Its the other way around. Undo gets filled up and from there a background process, RVWR writes this content into the Flashback logs. Undo can't be retained for a very long period of time. Theoretically, there can be a very long duration but practically its impossible. That's why Oracle has given Flashback logs. The idea is that in the case, some thing terrible has gone wrong (logically) with lots of tables than rather than sitting and doing either, incomplete recovery of the database and/or Flashback for the tables one by one, which both are time consuming and error prone,its better to go with Flashback logs.
Would the contents of Flashback logs and Undo Logs be the same ?
In gernal , yes they are. But all that is contained in Undo does NOT go in the Flashback logs.
I believe undo information is stored in SGA and then the Undo Logs.
Undo is an old copy of the block change and its sent to the Undo Segment immediately when you do the block change. Undo is not required to be kept in the Buffer Cache as long as some one doesn't need to have a read consistent copy of that block which you have changed.
HTH
Aman....

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Flashback and UNDO

I have a database with UNDO parameter "log_archive_dest" defined in the init file. When I tried to define the flashback parameter "db_recovery_file_dest" after I mounted the DB in SQL if got a "ORA-16019: cannot use db_recovery_file_dest with LOG_ARCHIVE_DEST" error message. Does using flashback mean I cannot have auto UNDO enabled in the database at the same time?

you can use auto undo with flashback, db_recovery_file_dest will be used for archived log destination.

Flashback and transaction query very slow

Hello. I was wondering if anyone else has seen transaction queries be really slow and if there is anything I can do to speed it up? Here is my situation:
I have a database with about 50 tables. We need to allow the user to go back to a point in time and "undo" what they have done. I can't use flashback table because multiple users can be making changes to the same table (different records) and I can't undo what the other users have done. So I must use the finer granularity of undoing each transaction.
I have not had a problem with the queries, etc. I basically get a cursor to all the transactions in each of the tables and order them backwards (since all the business rules must be observed). However, getting this cursor takes forever. From that cursor, I can execute the undo_sql. In fact, I once had a cursor that did "union all" on each table and even if the user only modified 1 table, it took way too long. So now I do a quick count based on the ROWSCN (running 10g and tables have ROWDEPENDANCIES) being in the time needed to find out if this table has been touched. Based on that, I can create a cursor only for the tables that have been touched. This helps. But it is still slow especially compared to any other query I have. And if the user did touch a lot of tables, it is still way too slow.
Here is an example of part of a query that is used on each table:
select xid, commit_scn, logon_user, undo_change#, operation, table_name, undo_sql
from flashback_transaction_query
where operation IN ('INSERT', 'UPDATE', 'DELETE')
and xid IN (select versions_xid
              from TABLE1
              versions between SCN p_scn and current_scn
              where system_id = p_system_id)
and table_name = UPPER('TABLE1')Any help is greatly appreciated.
-Carmine

Anyone?
Thanks,
-Carmine

Rollback and UNDO

Hi,
I'm confuse about Rollback and Undo concepts, can some one explain it to me please?
Felipe :)

This is a copy of a previous post I made some time ago:
There might be confusion while undo and rollback segment terms are used interchangeably in db world. It is due to the compatibility issue of oracle.
Undo
Oracle Database must have a method of maintaining information that is used to roll back, or undo, changes to the database. Such information consists of records of the actions of transactions, primarily before they are committed. These records are collectively referred to as undo.
Undo records are used to:
* Roll back transactions when a ROLLBACK statement is issued
* Recover the database
* Provide read consistency
* Analyze data as of an earlier point in time by using Flashback Query
When a ROLLBACK statement is issued, undo records are used to undo changes that were made to the database by the uncommitted transaction. During database recovery, undo records are used to undo any uncommitted changes applied from the redo log to the datafiles. Undo records provide read consistency by maintaining the before image of the data for users who are accessing the data at the same time that another user is changing it.
Undo vs Rollback
Earlier releases of Oracle Database used rollback segments to store undo. Oracle9i introduced automatic undo management, which simplifies undo space management by eliminating the complexities associated with rollback segment management. Oracle strongly recommends (Oracle 9i and on words) to use undo tablespace (automatic undo management) to manage undo rather than rollback segments.
To see the undo management mode and other undo related information of database-
SQL> show parameter undo
NAME TYPE VALUE
undo_management string AUTO
undo_retention integer 900
undo_tablespace string UNDOTBS1
Since the advent of Oracle9i, less time-consuming and suggested way is—using Automatic Undo Management—in which Oracle Database creates and manages rollback segments (now called “undo segments”) in a special-purpose undo tablespace. Unlike with rollback segments, we don’t need to create or manage individual undo segments—Oracle Database does that for you when you create the undo tablespace. All transactions in an instance share a single undo tablespace. Any executing transaction can consume free space in the undo tablespace, and when the transaction completes, its undo space is freed (depending on how it’s been sized and a few other factors, like undo retention). Thus, space for undo segments is dynamically allocated, consumed, freed, and reused—all under the control of Oracle Database, rather than manual management by someone.
Switching Rollback to Undo
1. We have to create an Undo tablespace. Oracle provides a function (10g and up) that provides information on how to size new undo tablespace based on the configuration and usage of the rollback segments in the system.
DECLARE
utbsiz_in_MB NUMBER;
BEGIN
utbsiz_in_MB ;= DBMS_UNDO_ADV.RBU_MIGRATION;
end;
CREATE UNDO TABLESPACE UNDOTBS
DATAFILE ‘/oradata/dbf/undotbs_1.dbf’
SIZE 100M AUTOEXTEND ON NEXT 10M
MAXSIZE UNLIMITED RETENTION NOGUARANTEE;
Note: In undo tablespace creation, “SEGMENT SPACE MANAGEMENT AUTO” can not be set
2.Change system parameters
SQL> alter system set undo_retention=900 scope=both;
SQL> alter system set undo_tablespace=UNDOTBS scope=both;
SQL> alter system set undo_management=AUTO scope=spfile;
SQL> shutdown immediate
SQL> startup
UNDO_MANAGEMENT is a static parameter. So database needs to be restarted.
Reference: 10gR2 Administration Guide and Concepts
Regards,
Francisco Munoz Alvarez

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....

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Best regards,
Christoph

Contents of flashback and undo ?

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