Heterogeneous Paxos 2.0: the Specs

We present Heterogeneous Paxos 2.0 (HP2.0), an improved version of Heterogeneous Paxos consensus algorithm (HP). In a nutshell, HP2.0 simplifies the algorithm logic, reduces bandwidth usage, and enables a more efficient implementation. HP2.0 is compatible with HP's requirements and has the same correctness properties. A formal specification of HP2.0 in TLA+ is available as a separate software artefact, with a formal proof of the key safety property of Agreement in TLAPS. This report provides an accessible account of HP2.0, of the design space in which it exists, and of the design choices that led us to our current system.