Обсуждение: Rollback with functions
Greetings! I have yet not fully understood the magic with transactions in combination with plpgsql functions. Assume I have a function create function foo() begin do stuff .... .... <--- here it fails .... end and a call to the function fails (as indicated in the code), will everything that has been done inside the function be automatically undone (rollbacked)? If I had added code for exceptions, like this create function foo() begin begin do stuff .... .... .... exception when others then .... <--- clean up code end; end Then I would need the "clean up code", or else there would be some changes in the database caused by all the commands that were actually run before the failure, right? So is there then any other reason besides having a way to tell exactly what went wrong (which I understand is a good thing ), to have the "clean up code"? (you might of course need to have more exception statements and add exceptions to the clean up code, and so on...
A B <gentosaker@gmail.com> writes: > Assume I have a function > create function foo() > begin > do stuff > .... > .... <--- here it fails > .... > end > and a call to the function fails (as indicated in the code), will > everything that has been done inside the function be automatically > undone (rollbacked)? Yes, it rolls back to the start of the transaction, which in this case is outside the function altogether. > If I had added code for exceptions, like this > create function foo() > begin > begin > do stuff > .... > .... > .... > exception when others then > .... <--- clean up code > end; > end > Then I would need the "clean up code", or else there would be some > changes in the database caused by all the commands that were actually > run before the failure, right? When control gets to the "clean up code", everything that happened inside the begin-block is already rolled back. (An exception is that the local variables of the function still have the values they had when the error was thrown. But effects out in the database have been undone.) regards, tom lane
On 2010-01-22, A B <gentosaker@gmail.com> wrote: > Greetings! > > I have yet not fully understood the magic with transactions in > combination with plpgsql functions. > > Assume I have a function > > create function foo() > begin > do stuff > .... > .... <--- here it fails > .... > end > > and a call to the function fails (as indicated in the code), will > everything that has been done inside the function be automatically > undone (rollbacked)? > > If I had added code for exceptions, like this > > create function foo() > begin > begin > do stuff > .... > .... > .... > exception when others then > .... <--- clean up code > end; > end > > Then I would need the "clean up code", or else there would be some > changes in the database caused by all the commands that were actually > run before the failure, right? some changes are immune to rollback (getting nextval from sequences being one such change) all other changes are undone when the function fails. > So is there then any other reason besides having a way to tell exactly > what went wrong (which I understand is a good thing ), to have the > "clean up code"? (you might of course need to have more exception > statements and add exceptions to the clean up code, and so on... If I want a function to do something when it encounters an error (instead of doing nothing but raising an exception), that is when I use exceptions.