A Universal Unique Identifier (UUID) is a 128 bit, unique identifier generated by the local system. It is unique across both space and time with respect to the space of all UUIDs.

A UUID can be used to tag records to ensure that the database records are uniquely identified regardless of which database they are stored in, for example, in a system where there are two separate physical databases containing accounting data from two different physical locations.

No centralized authority is responsible for assigning UUIDs. They can be generated on demand (10 million per second per machine if needed).

A UUID can be used for multiple purposes:

UUIDs are fixed sized (128 bits), which is small relative to other alternatives. This fixed small size lends itself well to sorting, ordering, and hashing of all sorts, sorting in databases, simple allocation, and ease of programming.