YouTube-like GUID

Question

Is it possible to generate short GUID like in YouTube (N7Et6c9nL9w)?

How can it be done? I want to use it in web app.

Answer 1

As others have mentioned, YouTube's VideoId is not technically a GUID since it's not inherently unique.

As per Wikipedia:

The total number of unique keys is 2¹²⁸ or 3.4×10³⁸. This number is so large that the probability of the same number being generated randomly twice is negligible.

The uniqueness YouTube's VideoId is maintained by their generator algorithm.

You can either write your own algorithm, or you can use some sort of random string generator and utilize the UNIQUE CONSTRAINT constraint in SQL to enforce its uniqueness.

First, create a UNIQUE CONSTRAINT in your database:

ALTER TABLE MyTable
ADD CONSTRAINT UniqueUrlId
UNIQUE (UrlId);

Then, for example, generate a random string (from philipproplesch's answer):

string shortUrl = System.Web.Security.Membership.GeneratePassword(11, 0);

If the generated UrlId is sufficiently random and sufficiently long you should rarely encounter the exception that is thrown when SQL encounters a duplicate UrlId. In such an event, you can easily handle the exception in your web app.

Answer 2

This id is probably not globally unique. GUID's should be globally unique as they include elements which should not occur elsewhere (the MAC address of the machine generating the ID, the time the ID was generated, etc.)

If what you need is an ID that is unique within your application, use a number fountain - perhaps encoding the value as a hexadecimal number. Every time you need an id, grab it from the number fountain.

If you have multiple servers allocating id's, you could grab a range of numbers (a few tens or thousands depending on how quickly you're allocating ids) and that should do the job. an 8 digit hex number will give you 4 billion ids - but your first id's will be a lot shorter.