Will virtual nodes have worse performance?

[Benyi Wang]

I have a small cluster with 3 nodes and installed Cassandra 2.1.2 from
DataStax YUM repository. I knew 2.1.2 is not recommended for production.

The problem I observed is:

   - When I use vnode with num_token=256, the read latency is about 20ms
   for 50 percentile.
   - If I disable vnode, the read latency is about 1ms for 50 percentile.

I'm wondering what is the root cause of the worse performance for vnode:

   - Is ver 2.1.2 the root cause?
   - num_token is too high for 3-node cluster?

Thanks.