RE: [WebStorage] Concerns on spec section 'Processing Model'

On Fri, 24 Jul 2009, Laxmi Narsimha Rao Oruganti wrote:
>
> That is all the responsibility of database system.  We don't need to 
> tell database systems on how to do it, we just need to tell them on what 
> to do.  Today database systems do have lock manager which takes care of 
> these responsibilities.
> 
> Coming to the question of failing transaction unpredictably, even with 
> current specification; transaction do fail.  For example, if there 
> exists a writer transaction which is already holding an exclusive lock, 
> this new thread would fail to acquire lock.  The failures would be 
> there.
> 
> Now the next question people would ask is on how do we make sure that 
> partial changes are not causing problem in case of a failure in the 
> middle of sequence of operations.  That is the responsibility of 
> transaction manager.  Note that transaction manager treats the whole 
> sequence as a single atomic unit.

As I understand it, with what is specced now, if you try to get a write 
transaction lock, it will only fail if it times out, which would probably 
be a symptom of a more serious bug anyway. There's never going to be a 
forced rollback; once you have got a transaction lock, you are not going 
to ever have it fail on you unexpectedly.

I think this is an important invariant, because otherwise script writers 
_will_ shoot themselves in the foot. These aren't professional database 
developers; Web authors span the gamut of developer experience from the 
novice who is writing code more by luck than by knowledge all the way to 
the UI designer who wound up stuck with the task for writing the UI logic 
but has no professional background in programing, let alone concurrency in 
databases. We can't be firing unexpected exceptions when their users 
happen to open two tabs to the same application at the same time, leaving 
data unsaved.

-- 
Ian Hickson               U+1047E                )\._.,--....,'``.    fL
http://ln.hixie.ch/       U+263A                /,   _.. \   _\  ;`._ ,.
Things that are impossible just take longer.   `._.-(,_..'--(,_..'`-.;.'

Received on Friday, 24 July 2009 08:37:30 UTC