Subject RE: [IBO] Multiple DB Apps on Single FDB file
Author Daniel R. Jimenez
> Sure is. Pick up the Tech Info sheet on DML Caching.
> >i.e. can the transaction component be told to only lock the record(s)
> which
> >is been updated
> Records which one transaction successfully posts are locked against
> updates
> by others, anyway. Table locking is totally unnecessary and undesirable
> for interactive applications. If Transaction A posts an update,
> Transaction B won't be allowed to post another update. The LockWait
> setting determines whether Tr. B will wait until Tr. A commits and attempt
> to update then, or whether it excepts immediately. Your handling of the
> Post operation should deal with this.
> If you want to block other transactions from updating a certain record if
> Tr. A starts editing the record (but hasn't posted anything yet) you can
> use PessimisticLocking. Since this method of pess. locking involves
> posting a dummy update as soon as Edit is called, you must take care with
> your triggers to ensure that pess. locking cannot cause an update trigger
> to fire and give unintended results. Fb 1.5's built-in pess. locking (FOR
> UPDATE WITH LOCK) might be useful to use instead, but it does have a lot
> of
> "undesirable issues" when used with datasets.
> > as well as having the FDB engine announce the
> >update/insertion to every other instance of the application which is
> >currently browsing the dataset which contains this particular record(s)?
> DMLCaching will take care of the announcing; but, of course, merely
> refreshing won't cause an unfinished concurrency transaction to "see" the
> outcome of others' commits. The application would need to respond by
> committing the concurrency transaction before refreshing. Refresh alone
> is
> OK for ReadCommitted transactions. With concurrency transactions, you'll
> need to work out carefully what you want to happen to pending work when
> the
> user gets a DMLCache notification.

Hi Helen,

Once more thank you very much for your help and pointers.