If the entity-groups have a (single) home and there is not any global coordination for transactions that means that there is a single machine in charge of that entity group. Allowing cross entity group transactions does not require that a single machine be in charge of all entities, it just means that the request processing process will need to coordinate with the machines in charge of each entity or that the machines in charge of each entity need would need to coordinate with each other as peers. That said I'm doubtful that entity groups have a single home as they would need to be mirrored around to actually scale, so it seems likely to me there is already coordination between the nodes mirroring the same entity group.
On Oct 4, 2:53 am, "David Symonds" <[EMAIL PROTECTED]> wrote: > On Sat, Oct 4, 2008 at 6:00 PM, Josh Heitzman <[EMAIL PROTECTED]> wrote: > > As far as transactions go, the global coordination is already there at > > the entity group level (if it wasn't, then there wouldn't be any > > transactions at all). Sure it will be more costly at the entity level > > then at the group level, but it will still be less costly then > > layering the equivalent on top of the data store API in the python > > application code. Allowing transactions spanning entity groups, > > doesn't mean that entity groups and non-spanning transactions need be > > eliminated. Leave it the application developer to choose the > > appropriate transaction type as needed. > > You're right, application-wide transactions don't have to subsume > entity-group transactions; you could, after all, put every entity in > your application in a single entity group. They are, however, still > inherently unscalable. Entity groups mean that global coordination is > *not* required, only that there is a "home" for each entity group. As > long as the entity groups are small, this responsibility can be split > across machines quite easily. > > Dave. --~--~---------~--~----~------------~-------~--~----~ 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 -~----------~----~----~----~------~----~------~--~---
