public int getMonitorGraphInterval(long testId, String targetIP, int imageWidth) {
		File monitorDataFile = new File(config.getHome().getPerfTestReportDirectory(String.valueOf(testId)),
				MONITOR_FILE_PREFIX + targetIP + ".data");

		int pointCount = Math.max(imageWidth, MAX_POINT_COUNT);
		int interval = 0;
		try (LineNumberReader lnr = new LineNumberReader(new InputStreamReader(new FileInputStream(monitorDataFile)))) {
			lnr.skip(monitorDataFile.length());
			int lineNumber = lnr.getLineNumber() + 1;
			interval = Math.max(lineNumber / pointCount, 1);
		} catch (FileNotFoundException e) {
			LOGGER.info("Monitor data file does not exist at {}", monitorDataFile);
		} catch (IOException e) {
			LOGGER.info("Error while getting monitor:{} data file:{}", targetIP, monitorDataFile);
		}
		return interval;
	}
Get the monitor data interval value. In the normal, the image width is 700, and if the data count is too big,
there will be too many points in the chart. So we will calculate the interval to get appropriate count of data to
display. For example, interval value "2" means, get one record for every "2" records.

@param testId     test id
@param targetIP   ip address of monitor target
@param imageWidth image with of the chart.
@return interval value.
ngrinder-controller/src/main/java/org/ngrinder/perftest/service/PerfTestService.java