Summary: I'm developing a persistent Java web application, and I need to make sure that all resources I persist have globally unique identifiers to prevent duplicates.
The Fine Print:
An online generator constructs a unique GUID according to RFC 4122. When creating a GUID, users should note the timestamp, clock sequence and the node ID -- such as a Media Access Control (MAC) address. This image shows an example of a GUID using hexadecimal digits.
A UUID is 36 characters long unique number. It is also known as a Globally Unique Identifier (GUID). A UUID is a class that represents an immutable Universally Unique Identifier (UUID).
Overview. UUID (Universally Unique Identifier), also known as GUID (Globally Unique Identifier) represents a 128-bit long value that is unique for all practical purposes.
Pretty sure UUIDs are "good enough". There are 340,282,366,920,938,463,463,374,607,431,770,000,000 UUIDs available.
http://www.wilybeagle.com/guid_store/guid_explain.htm
"To put these numbers into perspective, one's annual risk of being hit by a meteorite is estimated to be one chance in 17 billion, that means the probability is about 0.00000000006 (6 × 10−11), equivalent to the odds of creating a few tens of trillions of UUIDs in a year and having one duplicate. In other words, only after generating 1 billion UUIDs every second for the next 100 years, the probability of creating just one duplicate would be about 50%. The probability of one duplicate would be about 50% if every person on earth owns 600 million UUIDs"
http://en.wikipedia.org/wiki/Universally_Unique_Identifier
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