Distributed transactions have historically been implemented by the database community in the manner pioneered by the architects of System R* [22] in the 1980s. The primary mechanism by which System R*-style distributed transactions impede throughput and extend latency is the requirement of an agreement protocol between all participating machines at commit time to ensure atomicity and durability. To ensure isolation, all of a transaction’s locks must be held for the full duration of this agreement protocol, which is typi- cally two-phase commit. The problem with holding locks during the agreement protocol is that two-phase commit requiresmultiplenetworkround-tripsbe- tween all participating machines, and therefore the time required to run the protocol can often be.
