Notes on ‘Expert Oracle’ — No.9.6: Redo&Undo — Undo Log

1. Amount of Undo Log

    Delete > Update > Insert

    Operations on Indexed Columns > Operations on Non-indexed

2. What can cause "Snap Too Old"  exception?  => The undo segment is too small

3. How to make the undo segment not so small?

   a. Enlarge it, of course

      i.Enlarge UNDO_RETENTION, which should be larger than longest transaction

     ii.Set it by DBA manually 

   b. Query Tuning

   c. Do the block-cleanout by your self