I'm pretty sure the answer to your question is "banking is not an appropriate problem space for Google App Engine". Sure, you could eventually make it work by writing your own in-app 2pc layer, but why? There are other platforms that make this easier.
Consider also that there is no data robustness guarantee for GAE. Your data could go away without recourse. Use the right tool for the right job. If you need fine transaction control across large datasets, GAE is probably not for you. Most problem domains don't require the level of transactional integrity that banking demands. Jeff On Thu, Nov 26, 2009 at 7:40 PM, 风笑雪 <[email protected]> wrote: > I just watched some Google I/O videos about GAE yesterday, and I have > 2 questions about transaction. > > Assume I need to build a bank system, two clients (Alice and Bob) want > to transfer one's money to the other. > So when I create Alice and Bob, I must put them in the same entity group: > alice = User(name='Alice') > bob = User(parent=alice, name='Bob') > > If I have millions of clients, and they all have a chance to make a > deal with each other, then they should be all in the same entity > group: > adam = User(name='Adam') > alice = User(parent=adam,name='Alice') > bob = User(parent=adam, name='Bob') > chris = User(parent=adam, name='Chris') > ... > > As the presentation says, writes to the entity group is serialized, > and a write operation takes at least 10ms, a transaction needs at > least 1 reed and 3 writes, so I can't do more than 33 deals/sec, is it > scalable enough? > And having such a big entity group may easily cause high contention, > maybe most of the transactions will fail. > I wonder how could I break the huge group into small entity groups? > > > The second question is about the root entity. > The presentation says, root keeps a timestamp for the entire group. > But document also says, we can delete an ancestor, or just create a > Key for the ancestor that not exist to specify the parent of the new > entity. > So if the root has been deleted, or not exist at all, can this entity > group still transactional? > > -- > > You received this message because you are subscribed to the Google Groups > "Google App Engine" group. > To post to this group, send email to [email protected]. > To unsubscribe from this group, send email to > [email protected]. > For more options, visit this group at > http://groups.google.com/group/google-appengine?hl=en. > > > -- You received this message because you are subscribed to the Google Groups "Google App Engine" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/google-appengine?hl=en.
