17-25. Flashback Versions Query Considerations
The VERSIONS clause cannot be used to query
- External tables
- Temporary tables
- Fixed tables
- Views
The VERSIONS clause cannot span DDL commands
The VERSIONS clause in a SELECT statement cannot produce versions of rows across the DDL statements that change the structure of the corresponding tables. This means that the query stops producing rows after it reaches a time in the past when the table structure was changed.
What if I want to flashback version query after a DDL? is it possible?
Segment shrink operations are filtered out
Certain maintenance operations, such as a segment shrink, may move table rows across blocks. In this case, the version query filters out such phantom versions because the row data remains the same.
17-8. Flashback Database Considerations
From: Administration Workshop II 6-24
When the Flashback Database operatino completes, open the database:
- In read-only mode to verify that the correct target time or SCN was used with
select DBMS_FLASHBACK.GET_SYSTEM_CHANGE_NUMBER() from dual - With a
RESETLOGSoperation to allow for DML
17-7. Flashback Database: Reducing Restore Time
With Flashback Database, the time to recover a database is now proportional to the number of changes that need to be backed out (and not to the size of the database) because you do not have to restore data files.
The Oracle database periodically logs “before images” of data blocks in the Flashback Database logs. Block images can be reused to quickly back out the data file changes to any time at which flashback logs are captured just before the desired target time. Then, changes from the redo log files are applied to fill in the gap (since we only have periodic images so the gaps are filled with redo log).
Flashback Database can be applied to NOLOGGING operations such as direct load inserts (Administration Workshop II 6-29).
An alternative to FLASHBACK DATABASE is to create a Guaranteed Restore Point (Administration Workshop II 6-29). The latter does not require flashback logging to be enabled in your database and can return your database to its state at the specified SCN:
SQL> CREATE RESTORE POINT before_load 2> GUARANTEE FLASHBACK DATABASE;
8-23. Lock Modes
Need more info on these locking modes (though we often don’t use it since they are automatically obtained):
- ROW SHARE
- ROW EXCLUSIVE
- SHARE
- SHARE ROW EXCLUSIVE
- EXCLUSIVE
Explicación extensa de Oracle: http://youngcow.net/doc/oracle10g/server.102/b14220/consist.htm
Intento de explicación (cualquier cosa): http://mioracle.blogspot.com/2008/03/bloqueo-base-de-datos.html
