Re: [holger: Re: Logger for libgda]

[Rodrigo Moya <rodrigo gnome-db org>]

On 28 Nov 2000 23:09:30 +0100, David Marín Carreño wrote:
> On 28 Nov 2000, Rodrigo Moya wrote:
> 
> > 
> > so, you're going to save the changes? But this is not reliable at all.
> > Imagine I use:
> > 
> > UPDATE employees SET name = 'fulano';
> > 
> > ok, what you save here? that employees.name was set to 'fulano'? This is
> > ok, you've got a log of
> > what you've done in the DB. But, how will you recover the old data?
> 
> Seeking the last value of name before 'fulano'.
> 

which is in the logger, I suppose. And what if there is a change not
logged in? I mean, the DB
administrator could want to suppress logs for a while, and if so, your
system will revert the
data to the values set, say, 3 months ago? As I said, this is not
reliable.

Of course, we can say: once you use the logger, DON'T DISABLE IT, since
strange things could
happen. But of course, this is a step backwards for GDA, since we'll
have an unreliable
and very fond of errors system

> > 
> > This would be easy if you always used expressions such as:
> > 
> > UPDATE employees SET salary = salary + 200;
> > 
> > here, it's easy, you can recover by just doing
> > 
> > UPDATE employees SET salary = salary - 200;
> > 
> > But with other kind of expressions, I don't see the way you're going
> > to recover the old data when undoing.
> 
> Each time we change the database, we log it. Since the creation of the
> entry, until the last modifications. All are logged. So if we want to
> undo, we look for the last modification before the modification we want to
> undo.
> 

yes, but the first time you use the logger, what would you store? and,
as said before, what if
the logger is disabled for some time?

> > 
> > > > > Hope this problems can be solved, because i think having multiple
> > > > > undo levels on transactions is a great idea and a valuable feature
> > > > > for libgda!
> > > >
> > > > I also like the idea of having the logger in GDA, but only if we find
> > > > a good way of handling all these problems (and others that will
> > > > appear). But remember that if it's going to be in GDA, it should be as
> > > > generic as possible, making it suitable for ANY data source supported
> > > > by GDA.
> > > 
> > > I cannot see any problem here... Sorry ;-)
> > > 
> > the undoing stuff is the problem. I'd implement just a logger in 3/4 hours,
> > 
> > but the undoing stuff... I can't see the way we'll implement it.
> 
> I hope this message give you a clue.
> 

sorry, but not, I still see a big problem in the undoing stuff.