Paxos: What happens if the leader lost connection after commit in his own ledger but before multicast the success message?

Question

From the The Part-Time Parliament essay, what happens with the following situation.

The leader receives Voted(b, q) message from the majority and writes this degree in his own ledger, but lost connection before sending the Success(d) message.

with the Basic Protocol:

1. The new leader will re-proposes this decree but with a different ballot number (b+1)
2. The older leader reconnects after the new proposal passed
3. Now, we have the same decree passed twice with b and b+1

with the Multi-Decree Parliament

1. The new leader first fill the gap of b with no-op and then re-proposal the decree with b+1
2. After the old leader reconnects, b is associated with two values: the decree in old leader's eye and no-op in others' eye

What's wrong with my thoughts?

Answer 1

There is this statement in the essay: "The protocol’s requirements and assumptions were essentially the same as those of the later Parliament except that instead of containing a sequence of decrees, a ledger would have at most one decree."

The idea is that the ledger record number and ballot number - these are not same numbers. Each ledger number (each ledger position) may have more than one ballot to happen.

In your Basic Protocol example: there is a ledger with zero or one decrees. Even if the leader outage happens after consensus is reached - the final decree is still the same.