RE: Data Deletion in Tables with Foreign Keys

Dick- Do you have any experience with using "on delete cascade"? Do you know if it will be faster, or just easier? I was just curious how it worked behind the scenes and if it would still just be doing table scans.

Thanks again.
Erik

> -----Original Message-----
> From: dgoulet_at_vicr.com [SMTP:dgoulet_at_vicr.com]
> Sent: Thursday, November 01, 2001 10:10 AM
> To: Multiple recipients of list ORACLE-L
> Subject: Re:Data Deletion in Tables with Foreign Keys
>
> Erik,
>
> First off, do the foreign keys have the 'on delete cascade' option
> turned
> on? If not then do so as it makes keeping things in sync much easier.
> Actually
> in this scenario you don't have to worry about the child tables.
>
> Second, what do you mean by "The design of the application prohibits
> me from
> adding indexes to these tables. "? I've not seen any application that
> 'prohibits' adding indexes.
>
> Dick Goulet
>
> ____________________Reply Separator____________________
> Author: Erik Williams <ewilliams_at_brownco.com>
> Date: 11/1/2001 5:45 AM
>
> I need to prune data from a set of tables every day. I need to retain the
> last 90 days of information. Two of the tables, A and B, have foreign keys
> to a third, C. I cannot disable the constraints prior to deleting the
> data,
> because the system is 24/7. I have created a script that will delete the
> data from each of the tables with foreign keys first, then from the parent
> table. The problem I am having is the time it is taking to perform the
> deletions. The A and B tables are without indexes on the foreign key,
> because they very high volume insertion tables and very infrequent lookup.
> These tables are very large. The design of the application prohibits me
> from
> adding indexes to these tables.
>
> Here is the code:
>
> set serveroutput on
> set timing on
>
> DECLARE
> id number(15);
> dtm date;
> cnt number;
> cursor purge_c is
> select id
> from C
> where dtm < sysdate-90;
> BEGIN
> open purge_c;
> fetch purge_c into id;
> cnt := 0;
> while (purge_c%FOUND) loop
> cnt := cnt + 1;
> delete from A where id = id;
> delete from B where id = id;
> delete from C where id = id;
> commit;
> fetch purge_c into id;
> end loop;
> close purge_c;
> DBMS_OUTPUT.PUT_LINE('Number of sessions deleted: ' || cnt);
> END;
> /
>
> set timing off
> set serveroutput off
>
>
> I was thinking about creating another loop so that commits will only be
> done
> every 1000 deletions, but I think that the commits are a very a small
> percentage of the time compared to the table scans. I also considered
> partitioned tables, but I really don't want to go to that length. I was
> hoping to hear how other people handle this issue.
>
> Thanks.
>
> --
> Please see the official ORACLE-L FAQ: http://www.orafaq.com
> --
> Author: Erik Williams
> INET: ewilliams_at_brownco.com
>
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-- 
Please see the official ORACLE-L FAQ: http://www.orafaq.com
-- 
Author: Erik Williams
  INET: ewilliams_at_brownco.com

Fat City Network Services    -- (858) 538-5051  FAX: (858) 538-5051
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