So, I was watching the presentation on the HR datastore from the IO 2011 ( http://www.google.com/events/io/2011/sessions/more-9s-please-under-the-covers-of-the-high-replication-datastore.html ) and one thing caught my attention: the slides were showing the frontend instances running in more than one datacenter at the same time. So I understand that the memcached can lose data at any time and if the app is migrated between the datacenters all of the data in the cache are lost, however, running the app in two or more datacenters at a time each DC having a separate memcached cluster, that changes the properties quite significantly.
For example let's consider an app that uses some memcached key to keep a cursor where to write to the datastore, atomically incrementing it after each write. Such an app can detect if such a key is not present in the cache and determine what the cursor is by doing a query on the database and then add it to the cache atomically. If we add the possibility that there's another DC running the app w/ an independent memcached instance, such an app would just corrupt its own data. I hope I explained my concern well enough, and I would love to hear an answer from someone on the App Engine team. Thank you. -Sergey -- http://self.maluke.com/ -- You received this message because you are subscribed to the Google Groups "Google App Engine" group. To post to this group, send email to google-appengine@googlegroups.com. To unsubscribe from this group, send email to google-appengine+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/google-appengine?hl=en.
