I believe (you should test this) that it won't do any harm to set XG=true in master slave (it will just ignore you).
On Tue, Oct 18, 2011 at 1:28 PM, Jeff Schnitzer <[email protected]> wrote: > On Tue, Oct 18, 2011 at 9:07 AM, David Gay (Google) <[email protected]> > wrote: > > > > One other consideration: XG transactions do not work on master/slave. > > While the default could be different depending on whether HRD is used, > > that definitely has drawbacks. > > How can I detect if running on HRD vs M/S? I don't see anything on > SystemProperty. I could try starting an XG transaction and catching > the exception, but that would add an extra RPC to every Objectify > app's startup time :-( > > The XG issue seems pretty easily solved by documentation: > > 1) If you're running on M/S, you can only use one entity group in a txn. > 2) If you're running on HRD, you can use up to 5 entity groups in a txn. > 2a) If you use multiple entity groups in a txn, this is implemented > with 2pc and may produce surprising effects like > ConcurrentModificationException on read. This doesn't really matter > in practice if you use the RepeatInTransaction pattern. > > Put it this way: Non-ancestor queries work funky on the HRD too. Yet > I don't need to set a special flag just to issue non-ancestor queries. > Understanding eventual consistency and exotic transaction behavior is > just part of working with GAE. Magic flags that enable otherwise > expected behavior don't really help. > > Jeff > > -- > You received this message because you are subscribed to the Google Groups > "Google App Engine for Java" 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-java?hl=en. > > -- You received this message because you are subscribed to the Google Groups "Google App Engine for Java" 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-java?hl=en.
