what value I should assign to store->v.v0.datatype if I want to store JSON data?
right now this field ignored, so let it be zero
how to track CAS ? any API to call or I have to store them in data structure like map and track them by myself?
depends on your algorithm, if some of your operations require it, just store it in whatever struct you want in your application, if not, you can ignore it. little examples:
1. cas-insensitive case: keeping "the most recent event", in this case it is ok, if the key will be rewritten, most recent wins anyway
2. cas-sensitive case: tracking list of product ratings, here you aren't allowed to rewrite the object.