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Re: Limits to generality
Marko Vukolic <MVU@...>
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1) I would argue that all blockchains incl. Bitcoin and Ethereum store invalid transactions as well - in case of Bitcoin and Ethereum these are "orphaned blocks" that are still kept around in case their fork (branch), eventually prevails.
For me, the question of keeping only the validated ledger (in the parlance of the next consensus architecture proposal - NCAP) is the question of where one decides to make things visible to the "public". For instance, an implementation could wrap consensus service (from NCAP) together with (optimized) checkpoint as described there - and expose only the validated ledger, discarding raw ledger invisibly wrt. "public".
Re DoS, it is true that, unlike in Bitcoin or Ethereum, NCAP allows meaningless tx (e.g., garbage tx) to enter the raw ledger. To me, the main tools we would have against this are:
a) deployment-specific currency to charge transactions fees that get submitted to consensus service (ala Bitcoin, Ethereum)
b) rate-limiting the number of individual clients' outstanding requests (needs to be done by the consensus service)
c) as tx are signed - hold submitting peers accountable for garbage tx by a separate mechanism. This is certainly a possibility in permissioned implementations.
d) have consensus look into a transaction to say if it is a "legitimate" one. This last one goes into direction of having consenters as committers - it is not clear to me that we want this in the generic design - but this certainly remains an implementation/deployment possibility.
I am not sure that we would want to make d) a mandatory approach and sacrifice the possibility of entirely decoupling the consensus service from state/chaincode.
2) I agree - In NCAP this UUID roughly corresponds to tid (tx id) - perhaps we can amend that one to fit what you have in mind.
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