Re: [holger: Re: Logger for libgda]

[Rodrigo Moya <rodrigo gnome-db org>]

> > > > I don't understand what you mean here. The logging stuff should be optional,
> > > > so a client would call, for example:
> > > > 
> > > > gda_connection_enable_logger(Gda_Connection* cnc);
> > > > 
> > > > And what do you mean by accessing the database without logging?
> > > 
> > > A real secure system needs to log every data modification: the logger must
> > > not be enabled/disabled in this case. It should be always enabled... 
> The database's server log is the most reliable information in that case,
> client based logs are always to be considered ADDITIONAL information (but
> not reliable, secure, uncompromised information). However, i agree that
> putting logging into the provider/gda-server would make it more harder for
> people to circumvent client based logs (client meaning being libgda client).
> 
> > > 
> > > If we want this behaviour, we must program the logger in the
> > > server-side. The client mustn't be able to deactivate the logger...
> > > 
> ...
> > > For example: I am redefining a product for sale. I change the price, and
> > > the name of the product... Oh! I changed the wrong product... Please,
> > > undo... I press the undo button and...
> > > 
> > > * I look for my last action in "Log" table:
> > > 
> > > 1287 davefx  localhost 23:45:45 27/11/2000 Products 45 name="foo" 
> > > 
> > > log-ID  
> > >       username  
> > >                host       time      date        table_modified
> > >                                                      modified_entry
> > >                                                             action
> > > 
> > > OK. The last thing we did was setting a new name... So we seek the entries
> > > where the user davefx changed the 45th entry of Products table...
> > > 
> > > Here they are:
> > > 
> > > 644  davefx   localhost  13:23:21  15/11/2000 Products  45  new 
> > > 645  davefx   localhost  13:23:21  15/11/2000 Products  45  name="lulu" 
> > > 646  davefx   localhost  13:23:21  15/11/2000 Products  45  price=20.0
> > > 1286 davefx   localhost  23:44:34  27/11/2000 Products  45  price=32.05
> > > 
> > > 
> > > As we can see, the last name for the 45th product was "lulu". So it's
> > > done: the undoer saves "lulu" as name for 45th product.
> > > 
> > > The 1287th entrance to the log is marked as old. So we can make redoing
> > > this way too.
> > > 
> > > 
> > > Perhaps it is not an optimal way... but it should work.
> > > 
> Only if the first transaction you log is the first transaction you make. In
> each other cases, you have n-1 undos and can only ! :-)
> 
> Anyway, you have to fetch the data a transaction attempts to modify 
> from the server before applying that transaction, and log that data first.
> This would be a great hint for avoiding collision of multiple transactions
> from multiple systems:
>  Client a modifies some data and commits transaction. After that, client b
>  modifies the commited data (making it right again and applying some updates)
>  and commits his transaction. Now client a issues an undo. Updates of client
>  b would be lost, because they're not in the log of client a.
> 

yes, another problem that is raised now. Special care should be taken to
avoid this. And I ask
again: how could we do that?

> 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.

cheers