Flashback technologies

There are three distinct Flashback technologies available:

  • Flashback Database
    • Like pressing the rewind button on the entire database
    • Requires archivelog mode and the use of ALTER DATABASE OPEN RESETLOGS
    • Basic Steps:
      • shutdown;
      • mount;
      • flashback statement to a time, SCN or log switch sequence number;
      • open with resetlogs;
  • Flashback Query
    • Lets you query the database as it was in some point in the past, either for one select statement or by taking your whole session temporarily back in time.
    • Relies entirely on the use of UNDO segments
      • Flashback Versions makes it possible to select all versions of a row over a period of time, to show a history of what has happened to the row, when it happened, who did it, etc.
      • Flashback Transaction uses the Flashback Versions Query to identify which transaction caused the problem and uses SQL statements to undo the mistakes.
      • Flashback Table allows you to reverse all changes made to a table while leaving other tables intact.
  • Flashback Drop
    • Applies only to dropped tables.
    • When a table is dropped it is actually renamed to a system-generated name and not dropped until later if the space is needed by Oracle.
    • A Flashback Drop simply restores the name back to the table.
    • Can ONLY be used for objects removed with the DROP command (not truncate).
    • All associated indexes and permissions will also be restored.

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