Re: [Taler] replay and merchant backend/frontend protocol

[Florian Dold]

On 01/26/2016 12:01 AM, Christian Grothoff wrote:
> Well, in any case we need to very clearly define what the backend has to
> store.  Right now, the merchantdb only stores hashes of the contracts
> that have been paid, and never stores _anything_ just for the /contract
> requests.
> 
> What you suggest now will make /contract requests significantly more
> expensive, as even unpaid contracts will require a database transaction.
>  If we store
>  h_contract -> contract or
>  h_contract -> (contract, frontend_data)
> is almost irrelevant here.  For me, the real issue is that the merchant
> frontend can no longer assume that /contract requests are virtually free
> (we can probably do 10k EdDSA signatures/s, but only way fewer
> transactional DB commits/s).
> 
> But, you are right in that "somebody" has to do it, and it's probably
> better done once in the backend than in each frontend.

I don't think it's too bad to store
  h_contract -> (contract, frontend_data)
in the reference implementation backend.

We can always have optimized backends (in conjunction with specific
frontends) later, but storing all information will allow us to quickly
implement new frontends without having to come up with our own storage
scheme / mechanism every time.

My vote here would be on not prematurely optimizing things.

- Florian

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