[Bug?] Unwanted interpolated values in stacked graphs

Grafana InfluxDB
1

Hi all,

for a scientific project of a charging station operator, I want to aggregate the current charging power of all charge poles.

The values are stored in an influx-DB and are the current meter value of each charge point. The values are stored every 15 minutes in the database.

The query is as following:
SELECT 4*DERIVATIVE(DISTINCT("value"),15m) FROM "meterValues" WHERE $timeFilter GROUP BY time(15m),evse fill(null)
where the “evse” is the name of the charge point, ‘value’ is the current meter value of the charge point.

Focussing on one specific value, the query inspector shows the result as expected:

...
"name": "meterValues",
            "tags": {
              "evse": "ZZ*XYZ*E2012*2"
            },
            "columns": [
              "time",
              "derivative"
            ],
            "values": [
              [
                1609279200000,
                45400
              ],
              [
                1609280100000,
                48272
              ],
              [
                1609337700000,
                334.125
              ],
              [
                1609338600000,
                44496
              ],
              [
                1609339500000,
                47260
              ]
            ]
...

There are two charging sessions recorded. One stops at 1609280100000 and the next starts at 1609337700000.

If I klick on this charge-point in the stacked graph, I see the correct presentation:

image
image1485×382 44.3 KB

But if I show all datapoints, Grafana shows values even when there are no measurements of this datapoint at that specific timestamp:
image
image1487×502 149 KB

(Additionally, there are ugly black areas at the bottom of each column)

I tried all variants of fill(), but it has no effect. As you see from the query result and the single-column presentation, the values themselves are obviously corrent, but in fails in the presentation.

Any hint from the community?

Thanks in advance :slight_smile:
(I use Grafana 7.3.5)

2

Hi all,

it is getting worse: to get a better overview and a reduced dataset, I filtered by chargepoints with a “DE” prefix in the Socket-identifier (“EVSE-ID”):

SELECT 4*non_negative_DERIVATIVE(DISTINCT("value"),15m) FROM "meterValues" WHERE "evse" =~ /DE/ and $timeFilter GROUP BY time(15m),evse

This results in a really strange representation:
Sorted direction:

image
image1898×370 59.9 KB

And unsorted:

image
image1906×374 56.9 KB

[1/2]

3

Taking a closer look to DEXXXE0011*2:

image
image1903×373 63 KB

there is not even a measurement-point at the marked timestamp:
image
image1896×372 50 KB

as you can also see at the JSON-Source:

      {
        "name": "meterValues",
        "tags": {
          "evse": "DE*XXX*E0011*2"
        },
        "columns": [
          "time",
          "non_negative_derivative"
        ],
        "values": [
          [
            1609169400000,
            1800.48
          ],
          [
            1609175700000,
            3692
          ],
          [
            1609230600000,
            64.91803278688525
          ]
        ]
      },

Any explanation for these strange behaviour?

(I upgraded to 7.3.6)
[2/2]

4

I am experiencing the same problems in my installation of grafana 7.3.6. However, I do not have any track record for previous versions, so I can’t say wether this is a recently introduced bug or the shortcomings of the stacking logic.