Lightweight causal and atomic group multicast

The ISIS toolkit is a distributed programming environment based on virtually synchronous process groups and group communication We present a new family of protocols in support of this model Our approach revolves around a multicast primitive, called CBCAST, which implements fault-tolerant, causally ordered message delivery. CBCAST can be used directly, or extended into a totally ordered multicast primitive, called ABCAST. It normally delivers messages immediately upon reception, and imposes a space overhead proportional to the size of the groups to which the sender belongs, usually a small number. Both protocols have been implemented as part of a recent version of ISIS and we discuss some of the pragmatic issues that arose and the performance achieved. Our work leads us to conclude that process groups and group communication can achieve performance and scaling comparable to that of a raw message transport layer–a finding contradicting the widespread concern that this style of distributed computing may be unacceptably costly