title: App Engine High Replication Datastore
body: <p>I'm a total App Engine newbie, and I want to confirm my understanding of the high replication datastore. </p>
  
  <p>The documentation says that entity groups are a "unit of consistency", and that all data is eventually consistent. Along the same lines, it also says "queries across entity groups can be stale". </p>
  
  <p>Can someone provide some examples where queries can be "stale"? Is it saying I could potentially save an entity without any parent (ie. it's own group), then query for it very soon after and not find it? Does it also imply that if I want data to be always 100% up-to-date I need to save them all in the same entity group?</p>
  
  <p>Is the common workaround for this to use memcache to cache entities for a period of time longer than the average time it takes for data to become consistent across all data centers? What's the ballpark latency for that?</p>
  
  <p>Thanks</p>