public boolean isExpired(long timestamp, long expiredThreshold) {
        return timestamp - lastUpdateTimestamp > expiredThreshold;
    }
@param timestamp        of current time
@param expiredThreshold represents the duration between last update time and the time point removing from cache.
@return true means this metrics should be removed from cache.
oap-server/server-core/src/main/java/org/apache/skywalking/oap/server/core/analysis/metrics/Metrics.java