code: public Optional<OperatorBackPressureStats> getOperatorBackPressureStats(ExecutionJobVertex vertex) {
  		synchronized (lock) {
  			final OperatorBackPressureStats stats = operatorStatsCache.getIfPresent(vertex);
  			if (stats == null || backPressureStatsRefreshInterval <= System.currentTimeMillis() - stats.getEndTimestamp()) {
  				triggerStackTraceSampleInternal(vertex);
  			}
  			return Optional.ofNullable(stats);
  		}
  	}
docs: Returns back pressure statistics for a operator. Automatically triggers stack trace sampling
  if statistics are not available or outdated.
  
  @param vertex Operator to get the stats for.
  @return Back pressure statistics for an operator