Kevin, First the stuff MySQL calls UUID are GUID at least if you use Wikipedia definition: http://en.wikipedia.org/wiki/Globally… point. For example having 10 millions of users and spreading them on bunch of servers do you need to use SHA1 or similar ? I would not – I would instead use mapping table and use integer keys for users…

…use auto_increment but use certain partitioned sequences, for example you can have 256 growing sequences (with high byte used…completely separate problem which can be fixed in MySQL 5.1 Data Clustering This again applies … why UUID can do much better than SHA1 as Kevin proposes in the same post – …

…GUIDs. With truncated SHA1 (GUIDs) you can do some cool stuff. 1. If you’re using client side sharding …and exist checks without large amounts of memory. For example if you have a URL which is 255 … to build larger clustered databases. I just with MySQL had support for showing varbinary values on the …