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Thank you very much for taking the time - this did answer my question. If I may one more question related to this: Let's say I am using transactions as validation stops on a long list of inputs - So that the main program does some checking along the way, I have two choices, I can start with a BEGIN and do COMMIT at the very end, and possibly ROLLBACK everything once I get an error and start over. Alternatively (and this is obviously what I want to do), I can do BEGIN, then check say 1000 records, then COMMIT, then BEGIN, check 1000, COMMIT, etc. This way if I get an error, I need only rollback a little bit. The question is, how high is the overhead on BEGIN-COMMITs? In other words... Should I try to maybe change the program to do all checking in one pass, then write to the DB in another pass? (which is better if Transaction overhead is high, but worse if Transaction overhead is negligible). Thanks again! On 2013/06/08 17:16, Simon Slavin wrote:
On 8 Jun 2013, at 3:35pm, RSmith<[email protected]> wrote: 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.
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