  Building consensus sequences based on distributed, fault-tolerant consensus,
as used for replicated state machines, typically requires a separate
distributed state for every new consensus instance. Allocating and maintaining
this state causes significant overhead. In particular, freeing the distributed,
outdated states in a fault-tolerant way is not trivial and adds further
complexity and cost to the system.
  In this paper, we propose an extension to the single-decree Paxos protocol
that can learn a sequence of consensus decisions 'in-place', i.e. with a single
set of distributed states. Our protocol does not require dynamic log structures
and hence has no need for distributed log pruning, snapshotting, compaction, or
dynamic resource allocation.
  The protocol builds a fault-tolerant atomic register that supports arbitrary
read-modify-write operations. We use the concept of consistent quorums to
detect whether the previous consensus still needs to be consolidated or is
already finished so that the next consensus value can be safely proposed.
Reading a consolidated consensus is done without state modifications and is
thereby free of concurrency control and demand for serialisation. A proposer
that is not interrupted reaches agreement on consecutive consensus decisions
within a single message round-trip per decision by preparing the acceptors
eagerly with the previous request.
