Re: Row Lock

On Tue, 2003-10-07 at 12:20, Andreas Prohaska wrote:
> Even if this function would be implemented, your application would have
> to keep the ResultSet/Transaction open while the data is presented to
> the user in order to detect updates. So it would still be bad design.

I agree. Anyway that kind of algorithm is used also for normal (batch)
processing:
- <loop> for every row of the result set
- read the row
- elaborate
- check if the row has been modified, and, if not, store it. If it's
modified, rollback everything
- <loop>

So, a method to know if a row has been modified from the extern, is
needed.

> After all I think that it is not possible to implement this function
> because the backend itself handles updates/transactions in a way that
> does not allow this kind of check (at least: doesn't directly support
> it).
>
> The easiest way to come around this sort of problem is to use an
> optimistic control column (like an int) that is incremented
> with every row update. This allows you to detect changes by other
> users before making your own.

I'm not really sure what do you mean with the use of optimistic control
column, can you please give me some detail?

The problem (for me) is to find a solution that is functional also for
clients that uses the db other the mine.

In mysql there is the column type "timestamp" that does exactly this:
records the time of the last update of the row, so I need to check only
this value.

Is there something similar in postgresql?

Thanks,
Alex

> > Hello,
> > I also have to do a similar program and I ended up implementing this
> > exact scheme.
> > But I had to use hashes of the record to check if it was
> > changed because
> > it seems like the proper function, expressely designed for that is not
> > implementend: ResultSet.rowUpdated().
> >
> > Do you know if there are plans of supporting it?
> >
> > It would be a great boost for JDBC applications.
> >