guid

问题 I\'m trying to create globally-unique identifiers in JavaScript. I\'m not sure what routines are available on all browsers, how \"random\" and seeded the built-in random number generator is, etc.. The GUID / UUID should be at least 32 characters and should stay in the ASCII range to avoid trouble when passing them around. 回答1: UUIDs (Universally Unique IDentifier), also known as GUIDs (Globally Unique IDentifier), according to RFC 4122, are identifiers with a certain uniqueness guarantee. The

问题 I have an application that uses GUID as the Primary Key in almost all tables and I have read that there are issues about performance when using GUID as Primary Key. Honestly, I haven\'t seen any problem, but I\'m about to start a new application and I still want to use the GUIDs as the Primary Keys, but I was thinking of using a Composite Primary Key (The GUID and maybe another field.) I\'m using a GUID because they are nice and easy to manage when you have different environments such as \

问题 How safe is it to use UUID to uniquely identify something (I\'m using it for files uploaded to the server)? As I understand it, it is based off random numbers. However, it seems to me that given enough time, it would eventually repeat it self, just by pure chance. Is there a better system or a pattern of some type to alleviate this issue? 回答1: Very safe: the annual risk of a given person being hit by a meteorite is estimated to be one chance in 17 billion, which means the probability is about

问题 Is a GUID unique 100% of the time? Will it stay unique over multiple threads? 回答1: While each generated GUID is not guaranteed to be unique, the total number of unique keys (2 128 or 3.4×10 38 ) is so large that the probability of the same number being generated twice is very small. For example, consider the observable universe, which contains about 5×10 22 stars; every star could then have 6.8×10 15 universally unique GUIDs. From Wikipedia. These are some good articles on how a GUID is made