class_docstr: A memory backend which transfers the experiences from the rollout to the training worker using Redis Pub/Sub in
  Coach when distributed mode is used.
code: def sample(self, size):
      pass
  
imports: import redis
  import pickle
  import uuid
  import time
  from rl_coach.memories.backend.memory import MemoryBackend, MemoryBackendParameters
  from rl_coach.core_types import Transition, Episode, EnvironmentSteps, EnvironmentEpisodes
  from rl_coach.logger import screen
label_desc: Use image node_id 6 for calling the RedisPubSubBackend obj's underlying member method code with example usage: obj.sample(size) without return types