This proposal describes an alternative to Tickets for solving the problem of one transaction blocking another due to the sequence number ordering.
Instead of preemptively designating account sequence numbers to be used at a later time (using tickets), XRP Ledger can allow account transactions to happen out of sequence order.
The most important role of the Sequence number is that it makes each transaction on an account unique.
We can ensure that no sequence number is used more than once by storing what sequence numbers have been skipped for an account. An account would have:
- An account sequence representing the highest validated transaction sequence number + 1
- An optional (ordered) array of pairs of sequence numbers. Each pair represents a range of skipped sequence numbers