meaning for AgeOfLastAppliedOp in Replication MetricsSink

[Demai Ni]

hi,

A quick question to clarify this  AgeOfLastAppliedOp in MetricsSink.java. I
assume it is used as an indicator about how long for a Sink OP to be
applied; but instead, it is more like to show how long since the last Sink
OP applied

  /**
   * Set the age of the last applied operation
   *
   * @param timestamp The timestamp of the last operation applied.
   * @return the age that was set
   */
  public long setAgeOfLastAppliedOp(long timestamp) {
    lastTimestampForAge = timestamp;
    long age = System.currentTimeMillis() - lastTimestampForAge;
    rms.setGauge(SINK_AGE_OF_LAST_APPLIED_OP, age);
    return age;
  }

In the following scenario:
1) at 7:00am a sink op is applied, and the SINK_AGE_OF_LAST_APPLIED_OP is
set for example 100ms;
2) and then NO new Sink op occur.
3) when a refreshAgeOfLastAppliedOp() is invoked at 8:00am. Instead of
return the 100ms, the AgeOfLastAppliedOp become 1hour + 100ms, which
doesn't make sense, right?

should we put a check for (lastTimestampForAge != timestamp) before refresh
the age?

Thanks

Demai