Re: paper on Prevayler

Ralph Johnson wrote:

> Transactions need to be short. For some applications, "short"
> might mean 1000 ms, while to others they are no more than 1 ms.
> But you need to be have an idea of how long they are. If you
> are really writing Turing-complete transactions then you can't
> bound their length. So, I wouldn't agree that Prevayler has
> arbitrary transactions. It has rules for transactions, but
> those rules allow pretty complex transactions.

Fair enough, but my point was to distinguish Prevayler from other
"NoSQL" systems that only support trivial forms of atomic
operations -- pretty much just compare-and-set. Google's Chubby
and Yahoo's ZooKeeper are both prevalent systems that only
support that more limited kind of transaction: You can
conditionally update some set of values after comparing some
other set of values ('if A=3 and B=4 then set A=7 and C=5').

_Any_ practical programming has to avoid unbounded computation;
just because using a Turing-complete language _allows_ you to
write non-halting code doesn't mean actual programs can't be
proven to halt! Non-halting in real code is simply a bug (and
most commonly due simply to bad loop conditions leading to
infinite loops or bad base cases leading to infinite recursion).

Cheers,
Justin
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