Question

If we have a sequence to generate unique ID fields for a table, which of the 2 approaches is more efficient:

1. Create a trigger on insert, to populate the ID field by fetching nextval from sequence.
2. Calling nextval on the sequence in the application layer before inserting the object (or tuple) in the db.

EDIT: The application performs a mass upload. So assume thousands or a few millions of rows to be inserted each time the app runs. Would triggers from #1 be more efficient than calling the sequence within the app as mentioned in #2?

Answer 1

Since you are inserting a large number of rows, the most efficient approach would be to include the sequence.nextval as part of the SQL statement itself, i.e.

INSERT INTO table_name( table_id, <<other columns>> )
  VALUES( sequence_name.nextval, <<bind variables>> )

or

INSERT INTO table_name( table_id, <<other columns>> )
  SELECT sequence_name.nextval, <<other values>>
    FROM some_other_table

If you use a trigger, you will force a context shift from the SQL engine to the PL/SQL engine (and back again) for every row you insert. If you get the nextval separately, you’ll force an additional round-trip to the database server for every row. Neither of these are particularly costly if you do them once or twice. If you do them millions of times, though, the milliseconds add up to real time.