At 03:21 PM 8/27/2012, you wrote:
>On 8/24/12 7:18 PM, Ken Dibble wrote:
> >> >There are no guarantees in life. But the danger of sys(2015) lies in
> it's
> >> >generation
> >> >based on the timestamp. What are the chances of collision on this
> even not
> >> >concatenating the machine name?
> > Somewhat high, I believe. System clock ticks <> processor cycles. As I
> > understand it, in VFP RAND() uses the system clock, and RAND() will
> > generate the same number over and over and over in a tight loop on a fast
> > machine, until the system clock ticks over.
>
>Well, here's the test code I used:
>
>{{{
>create cursor temp (gid c(16))
>
>for n = 1 to 1000000
> insert into temp (gid) values (sys(2015))
>endfor
>
>select gid, count(*) from temp group by 1 having count(*) > 1
>}}}
>
>Let me know how many non-unique rows you get on your processor. I'm
>running XP on a
>virtual machine so that could be throttling my system enough to not see
>any issue.
None. AMD Athlon 64x Core Duo 5600+ @ 2.9 GHz.
It remains theoretically possible though. :)
>With auto-incrementing integer keys, how would you handle offline inserts
>without
>things getting incredibly complex?
I understand the advantages of using GUIDs when you need to able to synch
offline data.
I don't synch offline data in my apps. I'm not convinced there's an
advantage to GUIDs in situations where centralized key generation is always
available.
I don't use auto-increment to generate keys. I use my tried-and true
stand-alone procedure and pk lookup table. It's based on the one in Booth &
Sawyer's "Effective Techniques", with some modifications.
Ken Dibble
www.stic-cil.org
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