Re: Can these constraint be implemented in an RDBMS ?

"Christopher Browne" <cbbrowne_at_acm.org> wrote in message news:c22s6j$1o8h02$2_at_ID-125932.news.uni-berlin.de...
> After a long battle with technology, "ben brugman" <ben_at_niethier.nl>, an
earthling, wrote:
> > Reducing the example to 1-2 tables makes it less complex and
> > that was one of the points made. A situation to complex to
> > implement in an existing RDBMS.
>
> And this also expresses one of the vital principles of use of
> "scientific method;" if you are trying to demonstrate some effect, it
> is highly preferable to reduce the situation to being as simple as
> possible where the phenomenon may be observed.
>
> A recent discussion of deadlocks in MySQL was nicely demonstrated by
> the following quite simple example that leads to a deadlock.
>
> > use test;
> > drop table t;
> > create table t(id int, x int) type=innodb;
> > insert into t values(1,50);
> > insert into t values(2,100);
> > commit;
> >
> >
> > T1:
> > use test;
> > set transaction isolation level serializable;
> > set autocommit=0;
> > update t set x=-1 where id=1;
> >
> >
> > T2:
> > use test;
> > set transaction isolation level serializable;
> > set autocommit=0;
> > update t set x=-1 where id=2;
> >
> > -- T2 hangs despite trying to update a different row.
>
> A coworker has similarly pointed out the flaws in a database
> replication system based on a _simple_ set of three database updates
> that demonstrate how it falls into the trap of a particular flaw.
>
> You can't get away with the nonsense of baffling would-be users with a
> _purported_ fix if they actually have a simple case that shows why the
> system is broken. (And which might _still_ be broken, despite claims
> of a "remedy.")
> --
> output = reverse("gro.mca" "_at_" "enworbbc")
> http://www.ntlug.org/~cbbrowne/oses.html
> Rules of the Evil Overlord #190. "If my mad scientist/wizard tells me
> he has almost perfected my Superweapon but it still needs more
> testing, I will wait for him to complete the tests. No one ever
> conquered the world using a beta version."
> <http://www.eviloverlord.com/>

The Evil Overlord never heard of MSDOS 1.0 Received on Thu Mar 04 2004 - 00:05:34 CET