From: Logan Capaldo <logancapaldo@...>
Date: 2005-05-06T08:34:59+09:00
Subject: Re: [ANN] Transaction::Simple 1.3.0

On 5/5/05, Austin Ziegler <halostatue@gmail.com> wrote:
> On 5/5/05, John Lam <jlam@iunknown.com> wrote:
> > Yes - what you're saying does make sense.
> >
> > I was thinking about cases where you're performing transactions
> > against large objects, say a hash table.
> 
> Well, I do these against large objects. Transaction::Simple is a
> fundamental support library for PDF::Writer. Just about the only
> time it sees update is when I need to update it for PDF::Writer ;).
> 
> > Since the target objects don't know anything about transactions
> > (and you don't know anything about their internal state) then this
> > would wind up duplicating a lot of state.
> 
> Well, that's not really true. With Transaction::Simple, the target
> object does become transaction-aware -- but it has nothing to do
> with a "transaction manager" or database transactions.
> 
> > However, if an object were Tx aware, then it would know how to
> > manage its state in face of a transaction manager. Adding a single
> > entry to a hash table wouldn't require copying the entire table
> > first - you'd simply record the fact that you are adding a record
> > and add it at commit-time.
> 
> Right. This isn't a transaction log that can be replayed. This does
> the simplest possible thing (which is why there are a number of
> limitatiosn): it takes a Marshal.dump of the object.
> 
> > At this point you'll need to have 2-phase commit protocols -
> > telling each object to prepare to commit before actually
> > committing. Any object that fails to prepare to commit aborts the
> > entire Tx.
> 
> Well, I don't know if it's currently used, but DHH added
> Transaction::Simple support to ActiveRecord a while back so that
> when you do a transaction with ActiveRecord, if the database
> transaction fails, it also causes the object transaction to fail.
> 
> > This is probably a lot more complicated than what you have
> > envisioned (after all these are *Simple* transactions). I think
> > this will still be very useful for many situations where you
> > aren't modifying very large objects (or are not doing many such Tx
> > in parallel).
> 
> Perhaps. Something like this might be possible with a Builder
> object, but it would require a level of wrapping that I'm not -- at
> this point -- interested in dealing with.
> 
> -austin
> --
> Austin Ziegler * halostatue@gmail.com
>                * Alternate: austin@halostatue.ca
> 
> 

This is cool. Would things like this work?

v = SomeObject.new
v.extend(Transaction::Simple)

begin
   v.start_transaction
   v.someMethodThatMightRaiseAnExceptionLeavingTheObjectInAnInvalidState
   v.commit_transaction
rescue SaidException
      v.abort_transaction
end