  Today's practical partially synchronous Byzantine Fault Tolerant (BFT)
consensus protocols trade off low latency and high throughput. On the one end,
traditional BFT protocols such as PBFT and its derivatives optimize for
latency. They require, in fault-free executions, only 3 message exchanges to
commit, the optimum for BFT consensus. However, this class of protocols
typically relies on a single leader, hampering throughput scalability. On the
other end, a new class of so-called DAG-BFT protocols demonstrates how to
achieve highly scalable throughput by separating data dissemination from
consensus, and using every replica as proposer. Unfortunately, existing DAG-BFT
protocols pay a steep latency premium, requiring on average 10.5 message
exchanges to commit a transactions.
  This work aims to soften this tension and proposes Shoal++, a novel DAG-based
BFT consensus system that offers the throughput of DAGs while reducing commit
latency to an average of 4.5 message exchanges. Our empirical findings are
encouraging, showing that Shoal++ achieves throughput comparable to
state-of-the-art DAG BFT solutions while reducing latency by up to 60%.
