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Why is there missing data in historical data reports?

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When I generate a report with the historical data of some sensors, the sensor data is suddenly dropped or lost in the report. However, on the Live Data, 2 days, 30 days, and 365 days tabs in the PRTG web interface, PRTG correctly displays all data for these sensors.

Where is the missing data? How can I display this data in historic data graphs?

historic-data missing-values prtg reports

Created on Sep 8, 2014 2:51:10 PM by  Gerald Schoch [Paessler Support]

Last change on Jul 10, 2019 6:08:17 AM by  Maike Behnsen [Paessler Support]



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This article applies to PRTG Network Monitor 19 or later

Missing Data in Reports

Check your PRTG settings as listed below in this article if you encounter the following issues in your historic data reports:

  • You see 0 values, or
  • you see data that is missing completely, or
  • you see data that is dropped for some sensors,
  • but PRTG correctly displays data on the sensor tabs.

1. Purging Interval for Historic Sensor Data

Check the purging interval for Historic Sensor Data under Setup | System Administration | Core & Probes | Historic Data Purging.

If the time span covered by your report exceeds the time span of the purging interval for historic sensor data, the data in your report is missing because the historic data of the sensors that is included in your report has already been deleted.

Increase the number of days that historic sensor data is kept. See also PRTG Manual: Historic Data Purging.

2. Sensor Scanning Interval

The reason for missing data might also be a reduced scanning interval. Check if you have recently changed the scanning interval of these sensors.

To check it, go to the History tab of a sensor and take a look at the Messages column. You know that the scanning interval has been changed if there is an entry that looks like this, for example:

Edited. Scanning Interval/Scanning Interval: 10 minutes

Why does a reduction of the scanning interval matter?

Internal Test for Incorrect Calculations

When generating reports, PRTG ignores values in the calculation when an internally defined distance between two measurements is too big for a reasonable calculation.

The idea behind this mechanism is that if monitored values are too far apart, it is likely that there was a problem so that these values could cause an incorrect calculation. For example, overflows cannot be reliably detected in this case.

The formula for this time distance to ignore values for report calculations basically is

(3 * scanning interval) + (2 * timeout)

Note: This formula varies for different sensor types, based on our experience with particular sensors.

Example

Consider an SNMP sensor that has a scanning interval of 300 seconds (5 minutes) and the SNMP timeout value is 5 seconds. So the time span before which PRTG ignores values for the calculation is 3*300 (scanning interval) + 2*5 (timeout) = 910 seconds.

If you now reduce the scanning interval to 60 seconds (1 minute), PRTG only uses values from the last 190 seconds (3*60 + 2*5) for the report calculation. Because the scanning interval was 300 seconds before, PRTG now ignores all sensor values in the report calculation.

3. Spike Filter in Sensor Channels

Check if you have set a spike filter in the sensor channel settings of the sensor whose data is missing in your report.

The spike filter disregards very high or very low values that may result from faulty data transmission or incompatibilities on the monitored device. This setting prevents graphs from being unreadable.

Disable spike filtering if you want all measured values of the sensor to be written to your report.

Note: Use the spike filter with care. For SNMP sensors, check the SNMP Compatibility Options before you set a spike filter.

More

Sometimes, you might note a difference between the result of a historic data report and the corresponding graphs for 2, 30, or 365 days in the PRTG web interface.

This can happen because the graphs that are available on the sensor tabs (graphs for 2, 30, or 365 days) are cached, while historic data reports always poll the data directly from the PRTG monitoring database stored on the disk.

If the cached graph continues to look inconsistent, go to Setup | System Administration | Administrative Tools and try Recalculate PRTG Graph Data Cache (see PRTG User Manual: Administrative Tools).

Created on Sep 8, 2014 2:57:03 PM by  Gerald Schoch [Paessler Support]

Last change on Jul 25, 2019 4:56:06 AM by  Maike Behnsen [Paessler Support]



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Disclaimer: The information in the Paessler Knowledge Base comes without warranty of any kind. Use at your own risk. Before applying any instructions please exercise proper system administrator housekeeping. You must make sure that a proper backup of all your data is available.