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But...but...integers fit so much more nicely into a query string!
*duck and cover*
Seriously though, one of the few uses I've found for GUIDS is to allow the keys in your tables to be easily moved between different databases, for instance to move between a production and test DB. But otherwise integers are more efficient and easier to work with.
As for the uniqueness debate, who cares? Raise your hand if you have ever seen a duplicate GUID pop up in a real-world situation. It's like arguing about the randomness of pseudo-random number generators, it's a moot point for almost all real-world implementations.
If you're generating thousands of GUIDs per second in a system that you expect to be around for centuries, then maybe you should worry about it. Otherwise, it's like worrying about the server being taken out by a meteor hit. And even if you're unlucky enough to have a collision, you'd have to have a pretty fragile system for that to be a huge disaster; you'll probably have a dupe showing up in a join somewhere, not that hard to find and fix.
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Yup; my previous employer offered both standalone installations and a SAAS model where we hosted, and some of the primary keys were ints. When a client decided it was better to go from standalone to SAAS, merging was a giant PITA.
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They are also good for situations when you want an unpredictable value, such as a reference in a link for proving an email address.
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StatementTerminator wrote: easily moved between different databases
Yes indeed.
Reminds me of one place I worked where identities were used and the only way to view PROD data was to have a tool copy the data to a DEV database -- but the tool didn't allow the IDs to be copied  , the copied rows all had new IDs that didn't match PROD.
My argument isn't entirely against integers, but auto-increment integers over which the developer has no control. 
StatementTerminator wrote: integers are more efficient and easier to work with
My experience has been the opposite.
StatementTerminator wrote: As for the uniqueness debate, who cares?
'Xactly
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Guids are great for building object relationships client side without a need to hit a database to get the next available integer. Users should never see a Guid.
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It's a random number from a limited domain. Ask enough numbers, and you'll encounter the same number sooner or later - one doesn't need much math to explain the logic.
Bastard Programmer from Hell 
If you can't read my code, try converting it here[^]
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That's why I always repetitively hash and bitmask things until I end up with one byte.
And it has to be a human-readable byte, too, for those pesky tech support calls. 
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That's why I don't use GUIDs. 
"If A is a success in life, then A=x+y+z. (Work is x; y is play; and z is keeping your mouth shut.)"
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It must be unique, because it has "unique" in the name. Otherwise, it would have been a GNUID.
And anyway, I don't think the Internet would be lying at us like that.
~RaGE();
I think words like 'destiny' are a way of trying to find order where none exists. - Christian Graus
Do not feed the troll ! - Common proverb
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 +5
Sounds like someone just got high-speed internet last month.
There are only 10 types of people in the world, those who understand binary and those who don't.
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There is a finite number of possible values for a GUID. No finite number can be guaranteed unique.
It's not that difficult.
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If you're only talking about the random GUIDs, only 122 bits are actually random.
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Quote: For example, time value will roll over at less than 1400 years.
Oh My! Prepare for Year 3400 panic - all the COBOL code will have to be updated all over again.
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Of course it is possible to generate a non-unique GUIDs, but if you use a reliable implementation of a good generation algorithm, you can be reasonably confident that GUIDs will be unique within the context that matters. The only time I have seen problems was when using an unreliable implementation - NetWare 5 used to have problems with duplicate GUIDs being generated when timesync caused the clock to go backwards.
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Arguing about the uniqueness of GUIDs is pointless, given that they're integer numbers in a finite space, which means that soon or (most likely) later there's going to be a collision, however, for practical purposes we can say that they're unique.
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I've actually been burned twice in the same year by GUID collisions within unrelated software products from other companies. They are a very poor architecture choice.
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This may not be in the same spirit of fun that the article sets up, but I thought GUIDs were guaranteed unique because they are based on MAC addresses that are guaranteed as unique!? So proving MAC addresses are not unique would be a prerequisite?!
"Courtesy is the product of a mature, disciplined mind ... ridicule is lack of the same - DPM"
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But your server is generating GUIDs using the same MAC address, right? So it wouldn't be unique per GUID generated on that server. But you shouldn't have to worry about collisions with GUIDs generated on other machines, I guess.
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do {
myguid = getGUID();
} while(!exists(myguild))
This would solve the problem with unique, it'll execute almost only once for the next several thousand years. It'll never generate bug for "bad luck".
P.S. Sorry for my pseudocode, I write in javascript usually.
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I assume their algorithm is designed to use the MAC Address as a seed and is contructed to guarantee unique GUIDs given this.
You are right that there is a lot more to it than just the unique seed. I have never seen the algorithm and clearly never will. Sounds like a really interesting Math problem though. I would love to know the rest of the approach they used.
"Courtesy is the product of a mature, disciplined mind ... ridicule is lack of the same - DPM"
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Systems without network cards can generate GUIDs. What do they use for their MAC address? Yup.. zeros. A GUID also includes clock ticks of some sort or another that (they hope) tick faster than the system can request GUIDs. I seem to recall there's some bits in there for sequence number within a clock tick, or maybe systems just keep track of the last one issued and ensure they don't generate duplicates. I think there might be some other sources of mostly unique bits thrown in, like CPU serial numbers or something. The idea being that within a given uptime, of a given OS load, on a given system, they are guaranteed to be unique, and between systems, they are as unique as reasonably possible.
How are these bits packed into the GUID? It doesn't matter, no amount of deterministically massaging the bits will give you anything more unique. Massaging the source bits could obscure them and make backtracking to the original values for nefarious purposes more difficult, and I suspect its done. Using the source bits as seed for a pseudorandom number generator won't add uniqueness, but it is probably a pretty good, and inexpensive, way to deterministically massage the bits to obscure them.
GUIDs were never absolutely guaranteed to be unique, and I'd be willing to bet most of those sources of unique bits are no longer unique once one starts running GUID generation code in virtual machines.
We can program with only 1's, but if all you've got are zeros, you've got nothing.
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Great insights. Thanks.
This has always interested me. I guess I should try to research it better sometime.
"Courtesy is the product of a mature, disciplined mind ... ridicule is lack of the same - DPM"
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This has always interested me. I guess I should try to research it better sometime.
Thanks for the great insights.
"Courtesy is the product of a mature, disciplined mind ... ridicule is lack of the same - DPM"
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MS generates two types of GUID: one that is MAC address based and one that is time based. If you generate them sequentially, it will tke you some time to get a duplicate but if you generate them at random, it is a lot easier to get a duplicate. I have had duplicates several times.
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