Flashback - The Time Machine..
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Flashback technologies in Oracle allow users to view and recover data from the past. Flashback query allows querying past data by specifying a timestamp. Flashback table recovers an entire table to a time in the past without rolling back transactions. Flashback database recovers the entire database to a past time point using undo data and requires enabling flashback mode and setting up a flash recovery area.
Flashback - The Time Machine..
- 1. FLASHBACK – THE TIME MACHINE BY – NAVNEET UPNEJA
- 2. AGENDA • About Flashback • Flashback Technologies • Demo • Questions
- 3. FLASHBACK • Access to past much like a time machine. • Useful in case of User Errors or Logical Errors. • Can rollback Transaction with Database still remains Online. • Can be helpful to see the history of changes to data. • Can recover Table or database to point in time in the past. • New buffer in SGA: Flashback Buffer • New Background process: RVWR
- 4. FLASHBACK TECHNOLOGIES • Flashback Query • Flashback Table • Flashback Versions Query • Flashback Transaction Query • Flashback Transaction • DBMS_FLASHBACK • Flashback Drop • Flashback Database
- 5. FLASHBACK QUERY • Query data in the past. • Depends upon the data availability in Undo segments. • Can be used to recover lost data or undo some transaction. • Is used by using DzSELECT AS OFdz • Takes around 6 sec to record the flashback record. • SELECT * FROM FL_QUERY AS OF TIMESTAMP TO_TIMESTAMP('×tamp','DD-MON-YY HH24.MI.SS');
- 6. FLASHBACK VERSION QUERY • Retrieve different versions of rows during a given interval. • DzVersions Betweendz clause of Select statement is used. • Pseudocolumns are used: • Versions_startscn • Versions_starttime • Versions_endscn • Versions_endtime • Versions_xid • Versions_operation • Scripts used: fl_version_upd.sql fl_version.sql
- 7. FLASHBACK TRANSACTION QUERY • Retrieve Metadata and historical data for transaction/transactions. • flashback_transaction_query view is used to see the past transaction data. SELECT xid, operation, start_scn, commit_scn, logon_user, undo_sql FROM flashback_transaction_query WHERE xid in (select versions_xid from fl_query versions BETWEEN TIMESTAMP TO_TIMESTAMP('29-MAY-14 16.40.54', 'DD-MON-YY HH24.MI.SS') AND TO_TIMESTAMP('29-MAY-14 16.49.56', 'DD-MON-YY HH24.MI.SS'));
- 8. FLASHBACK TABLE • Will flashback a table to some time in past. • Use undo to flashback the table. • This is not a rollback, it’s a separate transaction. • Flashback table keep the constraints intact. • Enable Row movement on tables before Flashback table.
- 9. DBMS_FLASHBACK • Package used to rollback transaction/s. • Subprograms: • Enable_At_time • Transaction_backout • Disable • Must have DzFlashback any tabledz privilege. Example: exec dbms_flashback.transaction_backout(numtxns=>1,xids=>sys.xid_ array('030020006D070000'),options=>dbms_flashback.cascade);
- 10. FLASHBACK DROP • Getting back the dropped table. • Table is recreated (Re-named) from recycle bin. • Depends upon the availability of dropped table in recycle bin. • Cannot recover a table from dropped schema. Flashback table drop_table to before drop;
- 11. FLASHBACK DATABASE • Flashback Database to time in the past. • Needs Resetlogs to open the database. • Similar to point in time recovery but takes less time and less complex. • Db_recovery_file_dest=/data3/oracle/fast_recovery_area/ • Db_flashback_retention_target=1440; • Db_recovery_file_Dest=10G; • Alter database Flashback on; • Flashback database to timestamp to_timestamp('30-may-2014 14:51:09','dd-mon-yyyy hh24:mi:ss'); • Alter database open resetlogs;
- 12. • Restore Points • create restore point BEFORE_UPGRADE; • create restore point BEFORE_UPGRADE guarantee flashback database; • drop restore point BEFORE_UPGRADE;
- 13. SUMMARY • Flashback Query – no setup required – Just undo • Flashback Table – no setup required – Just undo • Flashback Drop – Recyclebin – on by default. • Flashback Versions - no setup required – Just undo • Flashback Database – Requires a flash recovery area / feature to be switched on. • Flashback Transaction – may require supplimental data • Flashback Data Archives – needs flashback tablespace