In one embodiment, one or more peers in an instant messaging group may each store {TAIL ~ a zone} of {HEAD ~ the instant messaging distributed index} 
In one embodiment , one or more peers in an instant messaging group may each store { TAIL ~ a zone } of { HEAD ~ the instant messaging distributed index }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD