INSERTS slow

Question

I have a batch process that comepletes in 3 hrs max if I process all the rows in one shot.
something like this
insert into dest_table
select * from
source_table;
But when I process the same at an entity level by passing in the entity pk the process is takes around 20 minutes on an average for each entity.
insert into dest_table
select * from
source_table
where entity_pk = pk;
Thanks
Why is this slow?

Answer 1

1) I assume that 20 minute per entity takes much longer than 3 hours total.
2) If something can be done in SQL, it will generally more efficient to do it in SQL. Oracle doesn't have to do a lot of context shifts between the SQL and PL/SQL engines. Oracle can often optimize queries differently if it knows that it is going to have to read every row from source_table than if you to do a lot of single-row reads. It's far more efficient to slurp up every row in the table via multi-block reads than to search an index and do a single block read for each and every row.
3) 20 minutes seems awfully long for the PL/SQL approach. Is the query using the primary key index?
Justin