Data Migration - Rollback segments

[rossman]

Does anybody know how to find out how large a transaction will be before the transaction occurs?<br>I am currently working with a team that is migating data from one system to another. The originating environment is Oracle 7x and the destination is Oracle 8x. I have set up different rollback segments and corresponding tablespaces. The problem is I have no Idea what the size of the various transactions will be. In some cases they will be small (insert statements) and in others they will be large(update statements). I know I can select the rollback segment for each transaction, but I need to know the size of the transaction to know which rollback seg to assign. Any help will be appreciated.<br>Thanks<br>Mike

 

[MikeLeung]

The simplest way to handle it is to create one large rollback segment for data migration. Then turn off all the normal rollback segment (offline) and leave only the big rollback segment online. Therefore, all the transactions will use the large rollback segment and you won't have any problem.<br><br>Once you finish with the migration, you can then change all the normal rollback segment online and then drop or turn off the big rollback segment.<br><br>Mike

 

[Guest_imported]

As Mikeleung Pointed out the best way is to online only 1 rollback segment so that the transaction may use that rollback segment. The size of each transaction can be known from the column - WRITES in V$ROLLSTAT view, by noting down the values before and after the transaction