Re: Duplicate timestamp(6): How is this possible?

From: Howard Latham <howard.latham_at_gmail.com>
Date: Thu, 20 Jan 2011 10:11:30 +0000
Message-ID: <AANLkTi=Vm6xPzBeFvgPp7m=u0cMrpgTarcrWcAWZfqfq_at_mail.gmail.com>

I was always taught to NEVER use TIME as a key. Even if your system works now what happens if you upgrade the hardware and it is so much faster that two rows can be inserted with in the granularity of the systems timer?

On 20 January 2011 10:00, Dunbar, Norman (Capgemini) < norman.dunbar.capgemini_at_environment-agency.gov.uk> wrote:

> Morning Howard,
>
> >> Not that I'm involved in building systems anymore but is
> >> there no longer required to use a sequence to guarantee a
> >> unique id for a record?
> It depends!
>
> You are just about to start the discussion on the merits of natural as
> opposed to synthetic keys now. :-)
>
> You would think that a timestamp(6) would be accurate enough to be
> unique for all situations - possibly excepting the flow of data from the
> LHC at CERN perhaps (16 TB daily apparently), but Oracle's TIMESTAMPS
> and TIMESTAMPS WITH TIME ZONEs cause their own problems.
>
> I'd never use a DATE as a primary key, computers work far too fast to
> allow second resolution to be unique. (Ok, I admit, as a very junior
> COBOL developer on an ICL 2966 mainframe, I did make the mistake of
> using a date as a key!)
>
>
>
> Cheers,
> Norm.
>
> Norman Dunbar
> Contract Senior Oracle DBA
> Capgemini Database Team (EA)
> Internal : 7 28 2051
> External : 0113 231 2051
>
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-- 
Howard A. Latham

Sent from my Nokia N97

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Received on Thu Jan 20 2011 - 04:11:30 CST