Re: schema/db design wrt performance

On Thu, 2003-01-16 at 10:02, Stephan Szabo wrote:
> On 16 Jan 2003, Ron Johnson wrote:
>
> > On Thu, 2003-01-16 at 09:39, Andrew Sullivan wrote:
> > > On Thu, Jan 16, 2003 at 08:34:38AM -0600, Ron Johnson wrote:
> > > > On Thu, 2003-01-16 at 08:20, Andrew Sullivan wrote:
> > >
> > > > > If a user has multiple connections and charges things to the same
> > > > > account in more than one connection at the same time, the
> > > > > transactions will have to be processed, effectively, in series: each
> > > > > one will have to wait for another to commit in order to complete.
> > > >
> > > > This is true even though the default transaction mode is
> > > > READ COMMITTED?
> > >
> > > Yes.  Remember, _both_ of these are doing SELECT. . .FOR UPDATE.
> > > Which means they both try to lock the corresponding record.  But they
> > > can't _both_ lock the same record; that's what the lock prevents.
> >
> > Could BEFORE INSERT|UPDATE|DELETE triggers perform the same
> > functionality while touching only the desired records, thus
> > decreasing conflict?
>
> It does limit it to the corresponding records, but if you
> say insert a row pointing at customer 1, and in another transaction
> insert a row pointing at customer 1, the second waits on the first.

2 points:

1. Don't you *want* TXN2 to wait on TXN1?
2. In an OLTP environment (heck, in *any* environment), the goal
   is to minimize txn length, so TXN2 shouldn't be waiting on
   TXN1 for more than a fraction of a second anyway.

Am I missing something?

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| Ron Johnson, Jr.     mailto:ron.l.johnson@cox.net          |
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