@Override
	Long defaultValue() {
		return 0L;
	}
Redis backed implementation that uses Redis keys to store and update the value. The naming strategy for keys in Redis
is "gauges." This means a Gauge named simpleGauge appears under the name "gauges.simpleGauge" in Redis.

@author Mark Pollack
spring-xd-analytics/src/main/java/org/springframework/xd/analytics/metrics/redis/RedisGaugeRepository.java