Subject Re: [ib-support] wait transactions and rollback
Author Danny Garcia Hernandez
Hi Ann and Woody

I think, that i have enough knowlege now (thanks to you) to face my
transactional problems. Finally i agree with both and i have learned my
proper concepts to confront the situation.

Thanks for all

""Woody"" <woody.tmw@...> escribi� en el mensaje
> From: "Ann Harrison" <aharrison@...>
> > My concern with live-lock is the possibility that
> > two transactions are interlocked. Transaction 1
> > updates record A and tries to update record B.
> > Transaction 2 updates record B and tries to update
> > record A.
> True, if there are 2 records being updated in one transaction. However,
> original intent of the poster was to just read and update a counter field.
> Such a simple action should not require a miriad of complexities to
> accomplish. A simple procedure that attempts a dummy edit on the record is
> enough in this case, IMO.
> > In a "wait" transaction the server notices that
> > the two transactions are waiting for each other
> > and produces a "deadlock" error - not just an
> > "update conflict".
> >
> > If both transactions are "no wait", then they
> > are, in fact, never waiting for each other.
> > The server has no way to recognize the problem,
> > so they continue until they system reboots.
> Unless a message is generated on the client to try again or quit trying.
> This is easy to accomplish and doesn't require much effort as far as
> programming goes.
> > My recommendation? Use a wait transaction, commit
> > or rollback when you see an "update conflict" error
> > and retry your operation, including re-reading the
> > records you based the change on. I realize that
> > the IBX (BDE?) version of "data driven" controls
> > makes that very awkward. My reaction to that is
> > use a better tool, but that's getting political.
> Too late, it's already political. <G> All tools except client datasets
> store the information locally are "data driven" and have the same type of
> issues. How you resolve the issue may depend on the type of components you
> use, but the basic problems still exist none-the-less. The best solution I
> have found is to work only with one record when editing information on a
> form, etc. That gives you the ability to test whether or not someone else
> already has the record "locked" while editing and keeps transactions as
> short as possible when working with live data.
> > What works is to issue a dummy update while you're
> > gathering data. The update can be to a specific
> > record, or to a generic "gateway" record. Until
> > that update succeeds, don't start reading data.
> > When it does, your update will protect your access
> > to the record (or set of records if you're using
> > a gateway.)
> I agree with this type of solution, however, reading data isn't really an
> issue, only modifying it, except in specific cases.
> Sorry to go on about this, Ann, but there are many people that I see post
> similar problems and the answers are generally skirting around the real
> issue which is the proper use of transactions. Too many times I've seen
> posts that say something like "My app hangs until the other user releases
> their transaction." Using wait transactions can cause just as serious a
> problem for some applications as using no-wait transactions. It's all in
> what you are trying to do. What works best in one situation may not work
> others. DIfferent situations require different and sometimes unique
> solutions.
> Woody (TMW)
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