Need Help: The problem with text key of MapFile

[lei wang]

Hi, friends
I need store the web pages(a huge one) in the MapFile of the hadoop, So i
did use the url as the key, and its type is "text", When  writring the
records into the mapfile, it give an error as "out of order", which type
should I choose to represent  the key "url", can anyone give me some detail
answer, thanks for you help.