two-phase commit and option pricing

[Dave Long]

> The two-phase commit protocol is a simple and widely-used protocol for
> ensuring atomicity of transactions involving multiple resources; a
> coordinator contacts the various resources (typically disk space in a
> computer setting) to reserve whatever resources are needed to commit a
> transaction, and if it succeeds in reserving all of the resources, it
> contacts them again to tell them to commit the transaction.
> 
> The most familiar example is the marriage ceremony (thanks to Gray and
> Reuter for the example):

Note the other parallels in formal marriages:

Atomicity
---------
One should be in a matrimonial eigenstate.  In states (of the union)
that support common-law marriage, the state doesn't require that one
formally get married, but it does require that one is either married
or not -- no superposition.

Consistency
-----------
Part of the reason for publishing banns (or secularly securing a 
marriage license) is to give an opportunity for discovery of any
impediments to the proposed union.  Violate integrity constraints
and the transaction aborts.

Durability
----------
In TP systems, the durable state is normally logged to disk.  In
social systems, durable state is kept by replication among large
numbers of people in the community.  Published banns were (are?)
to be read out to the entire congregation on at least three holy
days before the ceremony, and customs such as receptions ensure
turnout of sufficient numbers to form a reliable quorum.  (no
doubt church and state also keep durable records on their own,
but via paper, not simply* replication+gossip)

-Dave

* Looking at taxation at the time of the Magna Carta, it's easy
  to see that information was not an abundant commodity.  Taxable
  events were restricted to those sorts of activities which would
  be both infrequent and highly public: death, marriages (both of
  the taxers and taxees families), majority, and ransom.

  Today in the US I can even incur taxable events without taking
  any actions, simply by having income imputed to instruments.  I
  think it was Lessig who pointed out that in some ways, North
  Vietnam had a freer society in practice than ours, because even
  despite an opposite creed, the information infrastructure didn't
  exist there to keep track of most of a man's transactions.