Are you referring to the desire for evenly distributed primary keys?
It was necessary a couple years ago when we were working on a Sybase system
which only supported page-level locks. The tables were clustered around
their primary keys, meaning storage on physical disk grouped like-PKs
together. If the primary keys were generated in a sequential manner, they
would all attempt to write to the last page of the table/file, and therefore
always be in contention. Throughput dramatically increased with distributed
PKs. Now I am told Sybase supports row-level locking so this need may not be
so great.
Jim
> -----Original Message-----
> From: [EMAIL PROTECTED]
> [mailto:[EMAIL PROTECTED]]On Behalf Of Jim Archer
> Sent: Tuesday, June 26, 2001 4:38 PM
> To: [EMAIL PROTECTED]
> Subject: RE: [JBoss-user] Key generation by random numbers
>
>
> Hi Jim...
>
> I'm sorry, but I don't follow. Whats the advantage of this?
>
> --On Tuesday, June 26, 2001 3:57 PM -0400 Jim Kimball
> <[EMAIL PROTECTED]>
> wrote:
>
> > If you are looking for a simple unique ID generator that is also
> > (somewhat) evenly distributed, use a reverse timestamp. Use
> > System.getCurrentTimeMillis(), turn it into a string, then
> reverse it.
> >
> > If you have performance problems with such a simple
> algorithm, you might
> > want to write your own routine to do the reversing of a
> long without using
> > the generic String methods.
> >
> > Jim
> >
> >
> >> -----Original Message-----
> >> From: [EMAIL PROTECTED]
> >> [mailto:[EMAIL PROTECTED]]On Behalf Of
> >> [EMAIL PROTECTED]
> >> Sent: Tuesday, June 26, 2001 3:32 PM
> >> To: [EMAIL PROTECTED]
> >> Subject: Re: [JBoss-user] Key generation by random numbers
> >>
> >>
> >> On Tue, Jun 26, 2001 at 11:06:42AM -0400, Richard
> Kasperowski wrote:
> >> > [EMAIL PROTECTED] wrote:
> >> >
> >> > > As a follow-up to the debate on how to get
> auto-increment primary
> >> > > keys:
> >> > >
> >> > > Is it feasible to use a random number generator to
> >> generate primary
> >> > > keys? I don't really need my records to have steadily
> >> increasing keys
> >> > > and my number of records will presumably be much smaller
> >> than the size
> >> > > of my value space (4 billion? depending on data type for
> >> prim-key). So
> >> > > if I do something along the following when making a new record;
> >> > >
> >> > > boolean created = false;
> >> > > do
> >> > > {
> >> > > Long key = generateRandomLong();
> >> > > created = ejb.create(key, contents);
> >> > > }
> >> > > while (!created);
> >> >
> >> >
> >> > One problem with using random numbers is that they're not
> >> guaranteed to
> >> > be unique--two calls to generateRandomLong() can return the
> >> same value.
> >>
> >> Yes, but that isn't really a problem because you'll just
> try again and
> >> it happens sufficiently rarely that the extra time used is
> >> insignificant. At least, that would be the theory.
> >>
> >> > Another problem is that computing the next random
> number might be
> >> > relatively computationally expensive. I'd say serial
> >> numbers are better.
> >>
> >> If that is so, it would definately be a potential problem. I don't
> >> know much about the effeciency of the Java random number generator
> >> though.
> >>
> >> Cheers
> >> Bent D
> >> --
> >> Bent Dalager - [EMAIL PROTECTED] - http://www.pvv.org/~bcd
> >> powered by emacs
> >>
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> >>
> >
> >
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>
>
>
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