Best practice for performing inserts in a cursor - oracle

Question

I need to do some inserts in a cursor over about 300000 rows, this is however running slowly, any ideas on how i can make it run faster? Can i speed it up by batching the commits? So for example i would perform a commit after the 1000th row
DECLARE
CURSOR test_cursor IS
SELECT a from database.mytable
BEGIN
FOR curRow IN test_cursor LOOP
insert into tableb (testval)
values ('something');
commit;
END LOOP;
END;

Answer 1

300000 rows is not that many rows. Unless the rows are each extremely large, you should not commit in the middle of the batch.
Intermediate commits will only achieve:
additional overhead because each commit creates additional work,
loss of restartability in case of error (and loss of transactional integrity),
greater chance of running into ORA-1555
If your process is really a cursor with a single insert inside the loop, you should run a single statement:
BEGIN
INSERT INTO tableb (col1..coln) (SELECT col1..coln FROM database.mytable);
END;
If you still need extra performance, you could look into direct insert and parallel operation but It might be over-optimization with "only" 300k rows.
By far the single greatest optimization available to you is to think in term of sets instead of the traditional procedural approach that consists of batches of single row statements.

Answer 2

Or you can try this:
DECLARE
CURSOR test_cursor IS
SELECT col1 from table_a;
TYPE fetch_array IS TABLE OF test_cursor%ROWTYPE;
test_array fetch_array;
l_errors PLS_INTEGER;
l_dml_errors EXCEPTION;
PRAGMA EXCEPTION_INIT(l_dml_errors, -24381);
BEGIN
open test_cursor;
loop
fetch test_cursor bulk collect into test_array limit 10000;
forall i in 1..test_array.count save exceptions
insert into table_b(col1)
values(test_array(i).col1);
exit when test_cursor%notfound;
end loop;
close test_cursor;
commit;
EXCEPTION
WHEN l_dml_errors THEN
l_errors := SQL%BULK_EXCEPTIONS.COUNT;
dbms_output.put_line('Number of INSERT statements that failed: ' || l_errors);
FOR i IN 1 .. l_errors
LOOP
dbms_output.put_line('Error #' || i || ' at '|| 'iteration #' || SQL%BULK_EXCEPTIONS(i).ERROR_INDEX);
dbms_output.put_line('Error message is ' || SQLERRM(-SQL%BULK_EXCEPTIONS(i).ERROR_CODE));
END LOOP;
END;

Answer 3

I would not recommend a cursor approach for this. I use append parallel hints for situations like this. Most of the time your query literally runs N times as fast where N is the parallel degree. It is occasionally a good idea to bypass disaster recovery with nologging / noarchivelog.
For truly large migrations (dozens to hundreds of GB), I've found it's a good idea to batch on a table's natural key (date, usually). Some small amount of state around it can let you cancel + resume the migration at will if necessary.

Answer 4

May Be This will help you please try this
DECLARE
i number;
CURSOR test_cursor IS
SELECT a from database.mytable
BEGIN
FOR curRow IN test_cursor LOOP
insert into tableb (testval)
values ('something');
i:i+1;
if mod(i,1000)=0 then
commit;
end if;
END LOOP;
commit;
END;