Most of the time 'first reply' works even when using strong consistency because we cache the state of entity groups in all replicas. Though to read from a replica, it has to be up to date. So setting eventual consistency will help you if an entity group is written to a lot (likely not up to date) or rarely read (cache miss).
On Sun, Mar 18, 2012 at 8:29 PM, Jeff Schnitzer <[email protected]> wrote: > On Sat, Mar 17, 2012 at 6:27 PM, Waleed Abdulla <[email protected]> wrote: > > I thought HRD was supposed to solve the bad neighbor problem. As I read > > somewhere (don't have the reference handy right now), when your app > issues a > > read request, it's sent to multiple datastore replicas in parallel and > the > > app takes the data from whichever datastore replies first. > > I need to re-watch the "more 9s please" video to be sure, but I > believe "first reply wins" only works when you are using eventual > consistency mode - ie, when issuing a query on an indexed property > (always eventual) or doing a get-by-key in Consistency.EVENTUAL mode. > If you do a get-by-key in Consistency.STRONG mode (the default), you > will still need a quorum. > > Jeff > > -- > 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.
