I'm using Google cloud for back end of my Android app.
I save an entity:
It is possible that you reuse an entity's id and therefor overwrite the existing entity yourself every 7 days (well or a web crawler does).
Take a look at the datastore in the developers console. You should see only a few writes to your entity, but if i'm right you'll see something like 5 writes and more (the actual write count depends on the amount of indexes defined in your entity).
To make sure this doesn't happen you can simply set the
@Id Long id property of your greeting to
null before you call
save() so you'll get an auto generated id.