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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 suddenly is dropped or lost in the report. However, on the tabs in the PRTG webGUI for live data, 2 days, 30 days, and 365 days, PRTG displays all data correctly also 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]



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This article applies to PRTG Network Monitor 13 or later

Missing Data in Reports

If you encounter the following issues in your historic data reports

  • You see 0 values or data that is missing completely or is dropped for some sensors
  • PRTG displays data correctly on the sensor tabs … you might want to check the settings listed below in your PRTG installation.

1. Purging Interval for Historic Sensor Data

Check the purging interval for Historic Sensor Data in 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 included in your report has already been deleted.

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

2. Sensor Scanning Interval

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

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.

Workaround: Show Missing Values in Reports

If you want PRTG to use these values in your reports, try increasing the SNMP timeout value in section Credentials for SNMP Devices of the parent device of the sensor (or on group, probe, or root level), for example, to 90 seconds.

Attention: This workaround might result in frequent timeouts of SNMP sensors. In this case, please reduce the timeout value again after generating your report to prevent sensors from hanging in the timeout.

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

Did you know that PRTG displays graph data correctly because graph data is cached?

If you want PRTG to recalculate the cache for graph data, go to Setup | System Administration | Administrative Tools and click Go! for the Recalculate PRTG Graph Data Cache function. See PRTG User Manual: Administrative Tools.

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

Last change on Sep 25, 2018 4:21:25 PM by  Martina Wittmann [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.