Re: [xwiki-devs] [proposal] Add an xwiki-store module with a UUID user defined type.

On 11/10/2010 04:25 PM, Paul Libbrecht wrote: I remember reading this which said that UUIDs should be stored as binary rather than varchar. http://kekoav.com/blog/36-computers/58-uuids-as-primary-keys-in-mysql.html It appears that inserts can be given as SET id=0x1e8ef774581c102cbcfef1ab81872213 and (in mysql) can be returned in human readable form using SELECT HEX(id) FROM... http://dev.mysql.com/doc/refman/5.0/en/string-functions.html#function_hex Regarding indeces, my understanding is an index makes the column read as if it were sequential thus allowing for a binary search. Still a binary search means the number of load and compare operations is log2(length of table) so in a million entry table, 20 lookups are needed to find an entry (if the index is up to date). Perhaps I am splitting hairs on this, I know premature optimization is often a fool's errand. Another issue which is more difficult to measure is memory bounding. If a primary key column can be loaded into the processor cache then lookups will be orders of magnitude faster because loading from ram memory can take around 500 processor cycles. Unfortunately this kind of thing is rather magical unless one is programming in assembly. Those are my points, you are a user so I'm most interested to hear how you would benefit from storage as a string. Caleb