Delete 70,000,000 records from a Table .... Please help

Question

I am new to Oracle database. please help on
Oracle9i Enterprise Edition Release 9.2.0.1.0
We have one master table with 15,243,350 records and a child table 71,447,235 records in our Oracle database and the slow performance has been hitted our daily operation so bad recently. The two tables has quite intensive update during the day (around 60000 records a day)
I exported the whole database and import the database to a virtual machine for test.
I use the below statement to delete the record and it ran for around 20 hours (as this is on the test enviorment, there is no update activity during the delete process), it still takes quite long to delete.
delete from child_table where child_table.id in (select id from master_table where child_table.id=master_table.id and date <= to_date('01/08/2009 00:00:00','dd/mm/yyyy hh24:MILSS'))
Is that ok when I issue the same comment to delete the records in LIVE environment or please adivse other method(s) to do it....
BTW, do I need to rebuild the indices after deletion or Oracle will do it for me automatically ?

Answer 1

Hi,
I can think 2 ways to do it.
If you are deleting more than 80% (or I would say, a big chunk) of the data from the table. Lets say the original table is T1 (71 million rows). Create a table T2 whith the records you want to 'keep'. Rename T1 to T_old and rename T2 to T1. You can drop/truncate T_old later, when you don't need it.
All you have to manage here, are the foreign key constraints. You need to drop and re-create the foreign keys.
Another way. If you will be doing this deletion operation after every few days, I would recommend you partition table T1 by range. With one partition for each day. For deleting data, you can simply truncate partitions. That will be really quick and won't generate any redo/undo (or generate very little).
Regards