Thank you. So you are saying that each request basically does:
sql BEGIN
...
call appropriate controller function
...
sql COMMIT if success
What I do not understand is:
1) When called from cron, there is no automatic begin transaction,
so where does the begin come from?
2) When my controller function calls commit, how do I get another
begin to make a new transaction?
On Dec 29, 7:18 pm, mdipierro <mdipie...@cs.depaul.edu> wrote:
> A transaction starts when a request arrive and it is committed when a
> request returns. If there is an error that it not caught the
> transaction is rolledback.
>
> You can insert db.commit() (and db.rollback()) everywhere to break the
> transaction in smaller parts.
>
> Massimo
>
> On Dec 29, 8:54 pm, toomim <too...@gmail.com> wrote:
>
>
>
> > Mossimo, unfortunately this proposal does not solve the multi-
> > threading problem.
>
> > Can you tell me what the semantics of the "implicit begin" is? The
> > problem is that I do not know where begin is inserted. I thought it
> > happened at the beginning of every controller function call. That
> > would make it impossible to do multiple transactions (with multiple
> > begins) inside a single function. Is that assumption incorrect?
>
> > On Dec 29, 1:14 pm, mdipierro <mdipie...@cs.depaul.edu> wrote:
>
> > > Attention. There is no db.begin(). it is implicit. You can commit
> > > automatically but why not:
>
> > > while queue is not empty:
> > > task = db(~status.belongs(('done','failed'))).select(limitby=
> > > (0,1))[0]
> > > success = do_long_thing(task)
> > > if success:
> > > task.update(status = 'done')
> > > else:
> > > task.update(status = 'failed')
>
> > > On Dec 29, 2:10 pm, toomim <too...@gmail.com> wrote:
>
> > > > Very clever, thank you! If it crashes, these items will be lost
> > > > though. Is there a way to use transactions, to pull a single item at
> > > > a time from the table, process and delete it, within a single
> > > > transaction? Something like this:
>
> > > > while queue is not empty:
> > > > db.begin()
> > > > task = db(status != 'done').select(limitby=(0,1))[0]
> > > > task.update(status = 'done')
> > > > success = do_long_thing(task)
> > > > if success:
> > > > db.commit()
> > > > else:
> > > > db.rollback()
>
> > > > This way if the code fires an exception, or the computer crashes, the
> > > > database will roll back to its prior state automatically. The problem
> > > > is there is no begin statement in web2py. All begin statements seem
> > > > to be automatic. Is it possible to do one manually? Can I turn off
> > > > the automatic one?
>
> > > > On Dec 29, 12:04 am, Thadeus Burgess <thade...@thadeusb.com> wrote:
>
> > > > > Ah yes, so back to my original thought
>
> > > > > db(status == 'pending').update(status = 'pending-' + request.now)
>
> > > > > for db(status == 'pending-' + request.now).select():
> > > > > task.update_record(status = 'processing-' + request.now
> > > > > success = do_the_long_thing(task)
> > > > > fail
> > > > > if success:
> > > > > task.update_record(status = 'done')
>
> > > > > -Thadeus
>
> > > > > On Tue, Dec 29, 2009 at 1:52 AM, toomim <too...@gmail.com> wrote:
> > > > > > sk.update_record(status == 'proce
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