[Bitcoin-development] Consensus-enforced transaction replacement via sequence numbers

Mike Hearn mike at plan99.net
Wed May 27 10:11:26 UTC 2015


>
> Sequence numbers appear to have been originally intended as a mechanism
> for transaction replacement within the context of multi-party transaction
> construction, e.g. a micropayment channel.
>

Yes indeed they were. Satoshis mechanism was more general than micropayment
channels and could do HFT between any set of parties.


> As it happens, this cannot be made safe in the bitcoin protocol as
> deployed today, as there is no enforcement of the rule that miners include
> the most recent transaction in their blocks.
>

Safe is relative - this is the same logic the original replace-by-fee
argument uses. There's no enforcement that miners use any particular
ordering of transactions.

As I believe out of all proposed protocols Satoshi's is still the most
powerful, I would suggest that any change to the semantics on nSequence be
gated by a high bit or something, so the original meaning remains available
if/when resource scheduling and update flood damping are implemented. That
way people can try it out and if miners are breaking things too frequently
by ignoring the chronological ordering people can abandon protocols that
rely on it, and if they aren't they can proceed and benefit from the
greater flexibility.
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