Unique ids in database

I'm often seeing sites there IDs in urls looks like this: http://battl开发者_C百科elog.battlefield.com/bf3/forum/view/2811510711334022807/ How do they achieve this? This isn't regular autoincrement field. All ids seems to be random, but at fixed width. What are the benefits?

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One approach is to hide the real id (which is auto_increment) in a big random-looking number. For example:

• the first digit shows where the real Id starts
• the second digit shows the length
• the real id is located as determined by the previous two points
• everything else is random numbers up to a predefined length

Other options are:

• UUID - your example doesn't seem to use one, but it is universally unique identifier and is sometimes used.
• snowflake - twitter's new id generation method (or something like it)

Note that there are two important aspects here:

• don't let users easily guess IDs - this is handled by my example. But if there are protected resources, always protect them with a security check in addition to the unguessable ID
• provide cluster-wide unique ids - UUIDs, snowflake, and the likes, guarantee that an ID is unique across a cluster of machines.

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GUIDs/UUIDs such as this make it much harder to guess what will and won't be a valid ID number. Unless you have 10^18 users, the valid IDs will be very sparse compared to invalid ones.