A word on the implementation is in order. The SWIM
protocol layer at each group member ✡☞☛ maintains a buffer
of recent membership updates, along with a local count for
each buffer element. The local count specifies the number
of times the element has been piggybacked so far by ✡☛ ,
and is used to choose which elements to piggyback next.
Each element is piggybacked at most ➈➒➊ ✮⑥✰✜✲➓✫ times. If the
size of this buffer islarger than the maximum number of elements
that can be piggybacked on a single ping message (or
ack), elements that have been gossiped fewer times are preferred.
This is needed asthe protocol period is fixed, and the
rate of membership changes might temporarily overwhelm
the speed of dissemination. Preferring “younger” buffer elements
under such circumstances ensures that all membership
changes infect at least a few members - when the membership
change injection rate quiesces, these changes will
propagate through the rest of the group
