RE: HOW TO MAKE DELETION FAST

From: Karniotis, Stephen <Stephen_Karniotis_at_compuware.com>
Date: Thu, 27 Dec 2001 13:34:18 -0800
Message-ID: <F001.003E3581.20011227130027@fatcity.com>

OK. Everyone is assuming that your deletion of millions of rows may be expedited by simply truncating the table. Now, that would be perfect if you were simply emptying the table. However, if data is to remain in the table, then truncate is not the preferred choice. Here are some options along with some cautions.

PL/SQL procedure to perform delete - If you are deleting data based on values in another table, you could use a DELETE with a correlated sub-query to delete data. You could also add a counter to the PL/SQL code to delete 50,000 rows, commit the deletion and then continue. Unfortunately, if you make a mistake with the DELETE, you must recover the table from Offline archivedlogs. PL/SQL has never been the preferred choice for working with LOTS of data.
CTAS - Create Table as SELECT is another alternative. If you can create another table with only the data you want, delete the original table and simply rename this new table to the old name, you may speed up the process. Additionally, creating the table as UNRECOVERABLE helps as it reduces the amount of redo data generated by Oracle.
Use indexes with the delete process - If your delete process is referencing non-indexed columns, you are performing a full table scan for the DELETE. Using indexes will help performance significantly because the amount of data scanned is significantly reduced.
Traditional DELETE wit subquery - Same as PL/SQL offering except you cannot control the amount of data deleted between commits.

These are four options. Good luck.

Thank You

Stephen P. Karniotis
Technical Alliance Manager
Compuware Corporation
Direct: (248) 865-4350
Mobile: (248) 408-2918
Email: Stephen.Karniotis_at_Compuware.com
Web: www.compuware.com

-----Original Message-----
Sent: Thursday, December 27, 2001 3:15 PM

To:     Multiple recipients of list ORACLE-L
Subject:        RE: HOW TO MAKE DELETION FAST

TRUNCATE TABLE :-) -----Original Message-----
Sent: Thursday, December 27, 2001 3:00 PM To: Multiple recipients of list ORACLE-L

Hi Gurus
How to make deletetion of millions rows faster? Please suggest.
Thx
Seema

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