RateCollector helps to collect and calculate values (like rate, timeTick and etc...).

Tickler counts every time when called inc(),.

TimeRange is a range of timestamp contains the min-timestamp and max-timestamp.

TimeTickSender is to merge channel states updated by flow graph node and send to datacoord periodically TimeTickSender hold segmentStats cache for each channel, after send succeeds will clean the cache earlier than last sent timestamp.