protected void trackMembership(String redisKey) {
		zSetOperations.add(redisKey, 0.0D);
	}
Perform bookkeeping of entities managed by this repository. Uses a redis sorted set with a dummy value, which
happens to guarantee that keys for a given score are in sorted order.
spring-xd-analytics/src/main/java/org/springframework/xd/store/AbstractRedisRepository.java