Re: Better Delete method

Thank you Ahmed. So this code is doing data purge by creating a temp table which will be of similar structure(indexes and constraints needs to be exactly same) as of main table but is partitioned , so as to take advantage of partition exchange approach. But yes, it seems like DB resource/time consumption in this method is the same as method-2, which I mentioned in my initial post. And it does need downtime , because in between the CTAS and final partition exchange if any DML operation happens on the base table , that data will be missed.

And is it correct that in either of the ways(using CTAS with/without partition exchange), the primary key constraint can be created with a VALIDATE state only without much time and resource , if we first create the UNIQUE index and then create PK constraints in the VALIDATE state using that same unique index? Please correct me if I'm wrong.

On Sun, Jul 11, 2021 at 1:44 AM ahmed.fikri_at_t-online.de < ahmed.fikri_at_t-online.de> wrote:

> Hi,
>
>
>
> in the attached file is a method to delete data from big table using
> partition exchange (you have to enhance the method to use indexes....)
>
>
>
> Best regards
>
> Ahmed
>
>
>
>
>
>
>
> -----Original-Nachricht-----
>
> Betreff: Better Delete method
>
> Datum: 2021-07-10T21:47:55+0200
>
> Von: "Lok P" <loknath.73_at_gmail.com>
>
> An: "Oracle L" <oracle-l_at_freelists.org>
>
>
>
>
>
>
> Hello , this database version is 11.2.0.4 of Oracle Exadata. A table(say
> TAB1) is there holding ~900 million rows with size ~222GB and it's not
> partitioned. It has two indexes , one with a three column composite index
> with size ~98Gb and other is the primary key on one column with size ~23GB.
> As a part of the requirement we need to delete/purge 50% of its data from
> this table. No referential constraints exist here. So I wanted to
> understand, out of the two below, which is the best method to opt for? or
> any other possible better option?
>
> I can understand method-1 is achievable ONLINE, but is slower while
> method-2 will be faster. So if we can afford ~1-2hrs of downtime, is it
> good to go for method -2 as the delete approach. As because deleting 50%
> rows even in method-1 may also need a table move+index rebuild(which will
> again need downtime on 11.2) to lower the high water mark and make the
> indexes compact and back to normal. Please advise.
>
>
> Method-1:-
>
> steps- 1:
> In a cursor pick the ~450million rowids of the rows to be deleted based
> on filter criteria;
> step2:-
> Delete based on ROW_IDS in a bulk collect fashion with LIMIT 50K rows
> ids at oneshot and commit within loop.
>
> Method-2:-
>
> Step- 1
> Create a new table using CTAS a new table TAB1_BKP AS select * from
> TAB1 where (required filter criteria which will pick ~450 required rows);
> Step-2:-
> Create the composite index in parallel.to make it as fast as
> possible
> Create the unique index on the same column as there in PK.
> Create the primary constraints with NOVALIDATE(because creating it
> with validate may take a lot of time to validate existing data) using the
> above unique index (This operation should happen in seconds as the index is
> already created in the above step.)
> Rename the TAB1_BKP as TAB1 and TAB1 as TAB1_BKP(which can be served as
> backup for a few days and later dropped).
>
>
>
> 
>

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