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Insert to different schema - Optimization

Posted on 2011-03-22
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Last Modified: 2012-06-22
I have a simple insert statement with in my Stored Procedure:
Insert into Schema2.T1
Select * from Schema1.T1

There are 3 million rows and Toad shows cost as 17939.
How do I optimize this and quicken this load?

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Question by:codemonkey2480
3 Comments
 
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slightwv (䄆 Netminder) earned 250 total points
ID: 35193278
Use the APPEND hint to insert above the high water mark:

Insert /*+ APPEND */ into Schema2.T1
Select * from Schema1.T1



or

PL/SQL cursor loop with a commit every X rows to reduce undo?

declare
   counter number := 1;
begin
for i in (select * from Schema1.T1) loop
    insert into Schema2.T1(col1, col2) values(i.col1, i.col2);
    if mod(counter,1000)=0 then
         commit;
    end if;
    counter := counter+1;
end loop;
end;
/
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Assisted Solution

by:sdstuber
sdstuber earned 150 total points
ID: 35194074
ignore COST

using the append hint is the fastest way to do your insert.

I wouldn't try using a loop, that simply adds extra steps and since it's an insert, the undo should be minimal.

If you have triggers, constraints or indexes on the target table, those will all make the insert slower.

You might not be able to disable the triggers, but possibly you could drop the indexes and disable the constraints.
Then recreate the indexes when done and reenable the constraints.

If you follow those, make sure nobody else is going to touch that table while you are inserting or their access will be slow and could create corrupt data while the constraints are off

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Assisted Solution

by:josiethejewel
josiethejewel earned 100 total points
ID: 35197089
I would use the append hint and disable your indexes without dropping them. Disabling the indexes set them unusable so you will have to set your session to ignore unusable indexes. Once your data is inserted you can rebuild your indexes and everything will work fine. Every time oracle insert a row without the index disabled it has to rewrite the index. I did this for our database and took our loads( about 4 Million records) from 24 hours to about 2 hours.
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