What's your opinion on using UUIDs as database row identifiers, particularly in web apps?

I've always preferred to use long integers as primary keys in databases, for simplicity and (assumed) speed. But when using a REST or Rails-like URL scheme for object instances, I'd then end up with URLs like this:

http://example.com/user/783

And then the assumption is that there are also users with IDs of 782, 781, ..., 2, and 1. Assuming that the web app in question is secure enough to prevent people entering other numbers to view other users without authorization, a simple sequentially-assigned surrogate key also "leaks" the total number of instances (older than this one), in this case users, which might be privileged information. (For instance, I am user #726 in stackoverflow.)

Would a UUID/GUID be a better solution? Then I could set up URLs like this:

http://example.com/user/035a46e0-6550-11dd-ad8b-0800200c9a66

Not exactly succinct, but there's less implied information about users on display. Sure, it smacks of "security through obscurity" which is no substitute for proper security, but it seems at least a little more secure.

Is that benefit worth the cost and complexity of implementing UUIDs for web-addressable object instances? I think that I'd still want to use integer columns as database PKs just to speed up joins.

There's also the question of in-database representation of UUIDs. I know MySQL stores them as 36-character strings. Postgres seems to have a more efficient internal representation (128 bits?) but I haven't tried it myself. Anyone have any experience with this?

Update: for those who asked about just using the user name in the URL (e.g., http://example.com/user/yukondude), that works fine for object instances with names that are unique, but what about the zillions of web app objects that can really only be identified by number? Orders, transactions, invoices, duplicate image names, stackoverflow questions, ...

Solution 1:

I can't say about the web side of your question. But uuids are great for n-tier applications. PK generation can be decentralized: each client generates it's own pk without risk of collision. And the speed difference is generally small.

Make sure your database supports an efficient storage datatype (16 bytes, 128 bits). At the very least you can encode the uuid string in base64 and use char(22).

I've used them extensively with Firebird and do recommend.

Solution 2:

For what it's worth, I've seen a long running stored procedure (9+ seconds) drop to just a few hundred milliseconds of run time simply by switching from GUID primary keys to integers. That's not to say displaying a GUID is a bad idea, but as others have pointed out, joining on them, and indexing them, by definition, is not going to be anywhere near as fast as with integers.

Solution 3:

I can answer you that in SQL server if you use a uniqueidentifier (GUID) datatype and use the NEWID() function to create values you will get horrible fragmentation because of page splits. The reason is that when using NEWID() the value generated is not sequential. SQL 2005 added the NEWSEQUANTIAL() function to remedy that

One way to still use GUID and int is to have a guid and an int in a table so that the guid maps to the int. the guid is used externally but the int internally in the DB

for example

457180FB-C2EA-48DF-8BEF-458573DA1C10    1
9A70FF3C-B7DA-4593-93AE-4A8945943C8A    2

1 and 2 will be used in joins and the guids in the web app. This table will be pretty narrow and should be pretty fast to query

Solution 4:

Why couple your primary key with your URI?

Why not have your URI key be human readable (or unguessable, depending on your needs), and your primary index integer based, that way you get the best of both worlds. A lot of blog software does that, where the exposed id of the entry is identified by a 'slug', and the numeric id is hidden away inside of the system.

The added benefit here is that you now have a really nice URL structure, which is good for SEO. Obviously for a transaction this is not a good thing, but for something like stackoverflow, it is important (see URL up top...). Getting uniqueness isn't that difficult. If you are really concerned, store a hash of the slug inside a table somewhere, and do a lookup before insertion.

edit: Stackoverflow doesn't quite use the system I describe, see Guy's comment below.

Solution 5:

Rather than URLs like this:

http://example.com/user/783

Why not have:

http://example.com/user/yukondude

Which is friendlier to humans and doesn't leak that tiny bit of information?