Re: online redefinition used too much undo segment?

Zhu Chao wrote:
> hi, all,
> I am testing online redefinition in oracle 9.2, and I found it used
> too much rbs segment. While redefine (start_redef_table), for my 2GB
> table, it used 1.4GB rollback segment.
>
> That makes the online def not much useful for real big tables.
>
> I traced the session, it mainly did the insert /*+append*/ to
> populate the interim table. How can an insert statement use so much
> space? table has 19M rows. Table is narrow and I think for wider table
> it should not use similar rbs segment as this table has. This is the
> small tbale we have. We have tables with 300M rows which we target to
> convert to heap table.
>
> Anyone have real life experience using that tool? on big/busy
> tables?
>
> Thx
>

it must be late on a Friday for you to not see this but, I think you answered your own question...

"it mainly did the insert /*+append*/ to populate the interim table. How can an insert statement use so much space? table has 19M rows."

19M rows plus index(es), almost 2GB worth of datablocks etc, etc, etc...

It has to know what the original value was in case of failure so it can put it back which is why it is called ROLLBACK segments - otherwise you would be restoring from backup. Received on Fri Feb 24 2006 - 21:57:10 CST