Hmm... I'm not quite sure what you mean by function start point. It has been
a while since I did any embeded DB code. Everything now is through a JDBC
interface using standard SQL calls.
It sounds like you are wanting to be able to place a BEGIN statement within a
function call to make sure the calls within the function are in a transaction
and to be able to abort to that point. The issue I see with doing your
nested transactions vs. savepoint is that you would have to invent a way to
mark the end of the sub-transaction without a commit/rollback. Here is an
example:
BEGIN;
UPDATE...
function_a(){
BEGIN
UPDATE
function_b() {
BEGIN
UPDATE
} //end function_b
UPDATE
ABORT
} //end function_a
UPDATE
COMMIT;
How does the system know that the ABORT in the second half of function_a
should rollback to the BEGIN in function_a rather than the BEGIN in
function_b? The other issue I have seen is where you want to overwrite a
point, which you can usually do with a SAVEPOINT structure. This is
especially usefull in a looping structure where you want to be albe to roll
out one loop.
BEGIN;
UPDATE...
function_a(){
UPDATE
SAVEPOINT a ;
LOOP
function_b() {
SAVEPOINT b;
UPDATE
UPDATE
UPDATE
IF error ROLLBACK TO b ;
} //end function_b
UPDATE
SAVEPOINT a ;
END LOOP;
} //end function_a
UPDATE
COMMIT;
In this case the function_b may be something that tries to place something
somewhere and has multiple updates. If one of the updates fails then you
want to be able to rollback to the beginning loop value and let the next
iteration of the loop try out the next location. This type of structure is
especially usefull when there are many simultanious threads going on doing a
simular operation.
On Wednesday 27 November 2002 01:45 pm, Jean-Luc Lachance wrote:
> Jon,
>
> That is all fine and dandy, but aren't function start point candidate
> for a rollback to point?
> A transaction is currently implicitely started on function call, and we
> get into the same problem as with nested transaction when a function
> calls another one.
>
> Don't get me wrong, I thing SAVEPOINT and ROLLBACK TO is a great idea,
> but nested transaction is needed.
>
> JLL
