Re: Undo Generation

On 6/28/07, DBA Deepak <oracle.tutorials@xxxxxxxxx> wrote:

Very simplified comments inline:


SQL> delete myemp;

14 rows deleted.

SQL> select used_ublk,used_urec from v$session s,v$transaction t where
s.taddr=t.addr and s.username='SCOTT';

 USED_UBLK  USED_UREC
---------- ----------
         2         14



Entire rows written to undo.

SQL> update myemp set sal=sal*1.1;


14 rows updated.

 USED_UBLK  USED_UREC
---------- ----------
         1          9



only updated column  (with rowid and overhead ) written to undo

SQL> insert into myemp select * from emp;


14 rows created.

 USED_UBLK  USED_UREC
---------- ----------
         1          1



Only rowid (with overhead) written to undo.


--
Jared Still
Certifiable Oracle DBA and Part Time Perl Evangelist

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