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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