Duplicate Guid

**Nicholas Paldino [.NET/C# MVP]** · Nov 17 '05, 03:57 AM

Re: Duplicate Guid

Jay,

You probably have better odds at winning the lottery. Seriously.

What is your concern?

--
- Nicholas Paldino [.NET/C# MVP]
- mvp@spam.guard. caspershouse.co m

"Jay Douglas" <jayREMOVEIFNOT SPAM@squarei.co m> wrote in message
news:OHlTnMsZFH A.2288@TK2MSFTN GP14.phx.gbl...[color=blue]
> Does anybody know the odds of generating a duplicate guid?
>
> --
> Jay Douglas
> http://jaydouglas.com
>
>
>[/color]

**Jay Douglas** · Nov 17 '05, 03:58 AM

Re: Duplicate Guid

Just wondering ... just candy for the mind.

I've heard someone say the odds are about the same as winning the Texas
lottery 32 times.

I was just hoping a formula or a number.

I slept though statistics, so I can't come up with a good answer.

--
Jay Douglas

http://jaydouglas.com

"Nicholas Paldino [.NET/C# MVP]" <mvp@spam.guard .caspershouse.c om> wrote in
message news:O8jeiQsZFH A.2288@TK2MSFTN GP14.phx.gbl...[color=blue]
> Jay,
>
> You probably have better odds at winning the lottery. Seriously.
>
> What is your concern?
>
> --
> - Nicholas Paldino [.NET/C# MVP]
> - mvp@spam.guard. caspershouse.co m
>
> "Jay Douglas" <jayREMOVEIFNOT SPAM@squarei.co m> wrote in message
> news:OHlTnMsZFH A.2288@TK2MSFTN GP14.phx.gbl...[color=green]
>> Does anybody know the odds of generating a duplicate guid?
>>
>> --
>> Jay Douglas
>> http://jaydouglas.com
>>
>>
>>[/color]
>
>[/color]

**Jonathan Allen** · Nov 17 '05, 03:58 AM

Re: Duplicate Guid

Probably not possible. Two computers would have to be built as exactly the
same time, have the same MAC address (normally impossible), and generate a
GUID at exactly the same time. (Actually, I vaguely remember that MS doesn't
use the MAC address anymore, but I may be mistaken.)

--
Jonathan Allen

"Jay Douglas" <jayREMOVEIFNOT SPAM@squarei.co m> wrote in message
news:OHlTnMsZFH A.2288@TK2MSFTN GP14.phx.gbl...[color=blue]
> Does anybody know the odds of generating a duplicate guid?
>
> --
> Jay Douglas
> http://jaydouglas.com
>
>
>[/color]

**Nicholas Paldino [.NET/C# MVP]** · Nov 17 '05, 03:58 AM

Re: Duplicate Guid

Jay,

I remember reading something that said you had to generate 1000 new
GUIDs per second for the next 5000 years in order to come across a duplicate
(or something like that).

I wouldn't worry =)

--
- Nicholas Paldino [.NET/C# MVP]
- mvp@spam.guard. caspershouse.co m

"Jay Douglas" <jayREMOVEIFNOT SPAM@squarei.co m> wrote in message
news:Om6pzWsZFH A.3876@TK2MSFTN GP12.phx.gbl...[color=blue]
> Just wondering ... just candy for the mind.
>
> I've heard someone say the odds are about the same as winning the Texas
> lottery 32 times.
>
> I was just hoping a formula or a number.
>
> I slept though statistics, so I can't come up with a good answer.
>
> --
> Jay Douglas
> http://jaydouglas.com
>
>
> "Nicholas Paldino [.NET/C# MVP]" <mvp@spam.guard .caspershouse.c om> wrote
> in message news:O8jeiQsZFH A.2288@TK2MSFTN GP14.phx.gbl...[color=green]
>> Jay,
>>
>> You probably have better odds at winning the lottery. Seriously.
>>
>> What is your concern?
>>
>> --
>> - Nicholas Paldino [.NET/C# MVP]
>> - mvp@spam.guard. caspershouse.co m
>>
>> "Jay Douglas" <jayREMOVEIFNOT SPAM@squarei.co m> wrote in message
>> news:OHlTnMsZFH A.2288@TK2MSFTN GP14.phx.gbl...[color=darkred]
>>> Does anybody know the odds of generating a duplicate guid?
>>>
>>> --
>>> Jay Douglas
>>> http://jaydouglas.com
>>>
>>>
>>>[/color]
>>
>>[/color]
>
>[/color]

**Jay Douglas** · Nov 17 '05, 03:58 AM

Re: Duplicate Guid

Okay math wizards, a Guid is 32 hexidecimal digits.

Each digit can be A-F or 0-9 which amounts to 16.

so, 32 possiblities of 16 characters .. what's the formula

--
Jay Douglas

http://jaydouglas.com

"Jonathan Allen" <x@x.x> wrote in message
news:%23pL8IXsZ FHA.2520@TK2MSF TNGP09.phx.gbl. ..[color=blue]
> Probably not possible. Two computers would have to be built as exactly the
> same time, have the same MAC address (normally impossible), and generate a
> GUID at exactly the same time. (Actually, I vaguely remember that MS
> doesn't use the MAC address anymore, but I may be mistaken.)
>
> --
> Jonathan Allen
>
>
> "Jay Douglas" <jayREMOVEIFNOT SPAM@squarei.co m> wrote in message
> news:OHlTnMsZFH A.2288@TK2MSFTN GP14.phx.gbl...[color=green]
>> Does anybody know the odds of generating a duplicate guid?
>>
>> --
>> Jay Douglas
>> http://jaydouglas.com
>>
>>
>>[/color]
>
>[/color]

**Nicholas Paldino [.NET/C# MVP]** · Nov 17 '05, 03:58 AM

Re: Duplicate Guid

Let's make this simpler. It's a 128 bit number, which means that there
are 2^128 possibilities. That turns out to be:

3.4028236692093 846346337460743 177e+38

That's a large number.

--
- Nicholas Paldino [.NET/C# MVP]
- mvp@spam.guard. caspershouse.co m

"Jay Douglas" <jayREMOVEIFNOT SPAM@squarei.co m> wrote in message
news:Ouff6nsZFH A.2664@TK2MSFTN GP15.phx.gbl...[color=blue]
> Okay math wizards, a Guid is 32 hexidecimal digits.
>
> Each digit can be A-F or 0-9 which amounts to 16.
>
> so, 32 possiblities of 16 characters .. what's the formula
>
>
>
> --
> Jay Douglas
> http://jaydouglas.com
>
>
> "Jonathan Allen" <x@x.x> wrote in message
> news:%23pL8IXsZ FHA.2520@TK2MSF TNGP09.phx.gbl. ..[color=green]
>> Probably not possible. Two computers would have to be built as exactly
>> the same time, have the same MAC address (normally impossible), and
>> generate a GUID at exactly the same time. (Actually, I vaguely remember
>> that MS doesn't use the MAC address anymore, but I may be mistaken.)
>>
>> --
>> Jonathan Allen
>>
>>
>> "Jay Douglas" <jayREMOVEIFNOT SPAM@squarei.co m> wrote in message
>> news:OHlTnMsZFH A.2288@TK2MSFTN GP14.phx.gbl...[color=darkred]
>>> Does anybody know the odds of generating a duplicate guid?
>>>
>>> --
>>> Jay Douglas
>>> http://jaydouglas.com
>>>
>>>
>>>[/color]
>>
>>[/color]
>
>[/color]

**Rick Lones** · Nov 17 '05, 03:59 AM

Re: Duplicate Guid

Nicholas Paldino [.NET/C# MVP] wrote:[color=blue]
> Jay,
>
> I remember reading something that said you had to generate 1000 new
> GUIDs per second for the next 5000 years in order to come across a duplicate
> (or something like that).
>
> I wouldn't worry =)
>
>[/color]
Which would be the same as 1 million new GUIDs per second for the next 5 years,
or 1 billion per second for the next couple of days, would it not? If it's that
easy, I would worry.

-rick-

SP · Nov 17 '05, 03:59 AM

Re: Duplicate Guid

"Jay Douglas" <jayREMOVEIFNOT SPAM@squarei.co m> wrote in message
news:OHlTnMsZFH A.2288@TK2MSFTN GP14.phx.gbl...[color=blue]
> Does anybody know the odds of generating a duplicate guid?
>
> --
> Jay Douglas
> http://jaydouglas.com
>
>[/color]
Better than the odds of an incrementing numeric counter generating a
duplicate number.

SP

**Ravi Shankar** · Nov 17 '05, 04:00 AM

Re: Duplicate Guid

I thought its a combination of MAC address and current clock
tick(Year-Month-Day-HH:MM:SS:millis econd). So, probablility of getting a
duplicate is virtually 0.

"Jonathan Allen" wrote:
[color=blue]
> Probably not possible. Two computers would have to be built as exactly the
> same time, have the same MAC address (normally impossible), and generate a
> GUID at exactly the same time. (Actually, I vaguely remember that MS doesn't
> use the MAC address anymore, but I may be mistaken.)
>
> --
> Jonathan Allen
>
>
> "Jay Douglas" <jayREMOVEIFNOT SPAM@squarei.co m> wrote in message
> news:OHlTnMsZFH A.2288@TK2MSFTN GP14.phx.gbl...[color=green]
> > Does anybody know the odds of generating a duplicate guid?
> >
> > --
> > Jay Douglas
> > http://jaydouglas.com
> >
> >
> >[/color]
>
>
>[/color]

**cody** · Nov 17 '05, 04:02 AM

Re: Duplicate Guid

but you can never be sure. since the guid is generated using a hashfunction
of the values you mentioned, errors in the implemention of the hashfunction
can lead to duplicated guids.

"Ravi Shankar" <Ravi Shankar@discuss ions.microsoft. com> schrieb im
Newsbeitrag news:DFFD3CA5-528A-4219-8A25-075FDB7C8B26@mi crosoft.com...[color=blue]
> I thought its a combination of MAC address and current clock
> tick(Year-Month-Day-HH:MM:SS:millis econd). So, probablility of getting a
> duplicate is virtually 0.
>
>
> "Jonathan Allen" wrote:
>[color=green]
> > Probably not possible. Two computers would have to be built as exactly[/color][/color]
the[color=blue][color=green]
> > same time, have the same MAC address (normally impossible), and generate[/color][/color]
a[color=blue][color=green]
> > GUID at exactly the same time. (Actually, I vaguely remember that MS[/color][/color]
doesn't[color=blue][color=green]
> > use the MAC address anymore, but I may be mistaken.)
> >
> > --
> > Jonathan Allen
> >
> >
> > "Jay Douglas" <jayREMOVEIFNOT SPAM@squarei.co m> wrote in message
> > news:OHlTnMsZFH A.2288@TK2MSFTN GP14.phx.gbl...[color=darkred]
> > > Does anybody know the odds of generating a duplicate guid?
> > >
> > > --
> > > Jay Douglas
> > > http://jaydouglas.com
> > >
> > >
> > >[/color]
> >
> >
> >[/color][/color]

**Jay Douglas** · Nov 17 '05, 04:02 AM

Re: Duplicate Guid

I thought that MS stopped using the MAC address to create the guids since
the cheaper NIC cards were producing duplicate MAC addresses at an alarming
rate.

--
Jay Douglas

http://jaydouglas.com

"cody" <deutronium@gmx .de> wrote in message
news:eBqI6a4ZFH A.3808@TK2MSFTN GP09.phx.gbl...[color=blue]
> but you can never be sure. since the guid is generated using a
> hashfunction
> of the values you mentioned, errors in the implemention of the
> hashfunction
> can lead to duplicated guids.
>
> "Ravi Shankar" <Ravi Shankar@discuss ions.microsoft. com> schrieb im
> Newsbeitrag news:DFFD3CA5-528A-4219-8A25-075FDB7C8B26@mi crosoft.com...[color=green]
>> I thought its a combination of MAC address and current clock
>> tick(Year-Month-Day-HH:MM:SS:millis econd). So, probablility of getting a
>> duplicate is virtually 0.
>>
>>
>> "Jonathan Allen" wrote:
>>[color=darkred]
>> > Probably not possible. Two computers would have to be built as exactly[/color][/color]
> the[color=green][color=darkred]
>> > same time, have the same MAC address (normally impossible), and
>> > generate[/color][/color]
> a[color=green][color=darkred]
>> > GUID at exactly the same time. (Actually, I vaguely remember that MS[/color][/color]
> doesn't[color=green][color=darkred]
>> > use the MAC address anymore, but I may be mistaken.)
>> >
>> > --
>> > Jonathan Allen
>> >
>> >
>> > "Jay Douglas" <jayREMOVEIFNOT SPAM@squarei.co m> wrote in message
>> > news:OHlTnMsZFH A.2288@TK2MSFTN GP14.phx.gbl...
>> > > Does anybody know the odds of generating a duplicate guid?
>> > >
>> > > --
>> > > Jay Douglas
>> > > http://jaydouglas.com
>> > >
>> > >
>> > >
>> >
>> >
>> >[/color][/color]
>
>[/color]

**Jay Douglas** · Nov 17 '05, 04:02 AM

Re: Duplicate Guid

Nicholas,

Well put!

Taught me a little about coming up with the possibilities using the bit^2
deal too.

Thanks again.

--
Jay Douglas

http://jaydouglas.com

"Nicholas Paldino [.NET/C# MVP]" <mvp@spam.guard .caspershouse.c om> wrote in
message news:OZwCGssZFH A.3132@TK2MSFTN GP09.phx.gbl...[color=blue]
> Let's make this simpler. It's a 128 bit number, which means that there
> are 2^128 possibilities. That turns out to be:
>
> 3.4028236692093 846346337460743 177e+38
>
> That's a large number.
>
>
> --
> - Nicholas Paldino [.NET/C# MVP]
> - mvp@spam.guard. caspershouse.co m
>
> "Jay Douglas" <jayREMOVEIFNOT SPAM@squarei.co m> wrote in message
> news:Ouff6nsZFH A.2664@TK2MSFTN GP15.phx.gbl...[color=green]
>> Okay math wizards, a Guid is 32 hexidecimal digits.
>>
>> Each digit can be A-F or 0-9 which amounts to 16.
>>
>> so, 32 possiblities of 16 characters .. what's the formula
>>
>>
>>
>> --
>> Jay Douglas
>> http://jaydouglas.com
>>
>>
>> "Jonathan Allen" <x@x.x> wrote in message
>> news:%23pL8IXsZ FHA.2520@TK2MSF TNGP09.phx.gbl. ..[color=darkred]
>>> Probably not possible. Two computers would have to be built as exactly
>>> the same time, have the same MAC address (normally impossible), and
>>> generate a GUID at exactly the same time. (Actually, I vaguely remember
>>> that MS doesn't use the MAC address anymore, but I may be mistaken.)
>>>
>>> --
>>> Jonathan Allen
>>>
>>>
>>> "Jay Douglas" <jayREMOVEIFNOT SPAM@squarei.co m> wrote in message
>>> news:OHlTnMsZFH A.2288@TK2MSFTN GP14.phx.gbl...
>>>> Does anybody know the odds of generating a duplicate guid?
>>>>
>>>> --
>>>> Jay Douglas
>>>> http://jaydouglas.com
>>>>
>>>>
>>>>
>>>
>>>[/color]
>>
>>[/color]
>
>[/color]

**Willy Denoyette [MVP]** · Nov 17 '05, 04:04 AM

Re: Duplicate Guid

MAC addresses aren't used any more to generate GUID's.

Willy.

"Jonathan Allen" <x@x.x> wrote in message
news:%23pL8IXsZ FHA.2520@TK2MSF TNGP09.phx.gbl. ..[color=blue]
> Probably not possible. Two computers would have to be built as exactly the
> same time, have the same MAC address (normally impossible), and generate a
> GUID at exactly the same time. (Actually, I vaguely remember that MS
> doesn't use the MAC address anymore, but I may be mistaken.)
>
> --
> Jonathan Allen
>
>
> "Jay Douglas" <jayREMOVEIFNOT SPAM@squarei.co m> wrote in message
> news:OHlTnMsZFH A.2288@TK2MSFTN GP14.phx.gbl...[color=green]
>> Does anybody know the odds of generating a duplicate guid?
>>
>> --
>> Jay Douglas
>> http://jaydouglas.com
>>
>>
>>[/color]
>
>[/color]

**Willy Denoyette [MVP]** · Nov 17 '05, 04:04 AM

Re: Duplicate Guid

"Jay Douglas" <jayREMOVEIFNOT SPAM@squarei.co m> wrote in message
news:%23gGYnk4Z FHA.4068@TK2MSF TNGP10.phx.gbl. ..[color=blue]
>I thought that MS stopped using the MAC address to create the guids since
>the cheaper NIC cards were producing duplicate MAC addresses at an alarming
>rate.
>
> --
> Jay Douglas
> http://jaydouglas.com
>
>[/color]

That's right, microsoft doesn't use the DCE algorithm on NT based systems
(since NT4 SP4), but the reason was a bit of "privacy paranoia", people
didn't like to give away their MAC addresses through a GUID.

Willy.

Duplicate Guid

Duplicate Guid

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