On 8 Jun 2013, at 3:35pm, RSmith <[email protected]> wrote: > A) so to have: > BEGIN > SAVEPOINT A > ... > RELEASE A > SAVEPOINT B > ... > RELEASE B > ... > COMMIT; > > B) or to have: > BEGIN > SAVEPOINT A > ... > SAVEPOINT B > ... > RELEASE B > ... > RELEASE A > COMMIT; > > I realise both ways have code efficiency issues, but just is there a real > execution speed difference?
These two pieces of code do not do the same thing. (A) talks about three sets of changes: one overall set, which includes two different subsets. Consider you were updating your league tables after a day in which two tennis matches were played. You need to make a change to details about match A, then a change to details about match B, and you also need to make changes to your league positions. The change to details about match A have nothing to do with the change to details about match B. So you have released SAVEPOINT A before you start SAVEPOINT B. (B) talks about a nested set of changes. You do not want the change to SAVEPOINT A to happen unless the change to SAVEPOINT B worked. Here, suppose you are recording the result of a race. You have to modify both the details of the race and the individual stats of the winner. Here, if there is a problem with modifying the result of the race (SAVEPOINT B) then you need to make sure that you do not modify the stats of the individual runner (SAVEPOINT A) As you can see, the two options are suitable for different situations. You should use whatever structure reflects the changes you are making. But your basic question was about how long these things took. Assuming that you do reach RELEASE (and not ROLLBACK) on both, they will take near-enough the same time. However, the BEGIN/COMMIT in (B) is not needed because all the changes made are in at least one SAVEPOINT. Leaving it out may speed up your program slightly. THe outer SAVEPOINT has exactly the same effect as having a BEGIN/COMMIT. Simon. _______________________________________________ sqlite-users mailing list [email protected] http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
