1 2 Previous Next 15 Replies Latest reply: May 5, 2012 12:20 AM by JuanM RSS

    db file sequential read instead db file scatered  read in FTS

    JuanM
      Hi gurus!

      I hope you all are ok.

      I need some help understanding this.

      1. I have a 3 gb table called MYTABLE.
      2. I have this pl sql code.
      Cursor mycur is
      Select * from mytable;
      
      ...code
      Update mytable set col1=1;
      
      Open mycur;
      
      Loop
      Fetch mycur ....
      Exit when ...
      End loop;
      Close mycur;
      Commit;
      3. The execution plan shows FULL SCAN on table mytable.
      4. Longops show Table scan mytable.
      5. But, session wait events show me db file sequential read instead db file scatered read when a full table scan is performed.
      6. In p1 parameter shows file# 52, file# 53, file# 54. All these files are UNDOTBS files.

      I don't undertand why is reading UNDOTBS?
      What i am misunderstanding?

      Thanks in advance!

      Johnxjean
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