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docs(aggregators.derivative): add explanation of calculations #12758

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Mar 1, 2023
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docs(aggregators.derivative): add explanation of calculations #12758

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15 changes: 7 additions & 8 deletions plugins/aggregators/derivative/README.md
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Original file line number Diff line number Diff line change
Expand Up @@ -140,7 +140,7 @@ To avoid thinking about border values, we consider periods to be inclusive at
the start but exclusive in the end. Using `period = "10s"` and `max_roll_over =
0` we would get the following aggregates:

| timestamp | value | aggregate | explanantion |
| timestamp | value | aggregate | explanation |
|-----------|-------|-----------|--------------|
| 0 | 0.0 |
| 2 | 2.0 |
Expand All @@ -162,7 +162,7 @@ aggregator will emit the log messages `Same first and last event for "test",
skipping.`. This changes, if we use `max_roll_over = 1`, since now end
measurements of a period are taking as start for the next period.

| timestamp | value | aggregate | explanantion |
| timestamp | value | aggregate | explanation |
|-----------|-------|-----------|--------------|
| 0 | 0.0 |
| 2 | 2.0 | 1.0 | (2.0 - 0.0) / (2 - 0) |
Expand All @@ -183,25 +183,24 @@ There may be a slight difference in the calculation when using `max_roll_over`
compared to running without. To illustrate this, let us compare the derivatives
for `period = "7s"`.

| timestamp | value | `max_roll_over = 0` | `max_roll_over = 1` |
|-----------|-------|-----------|--------------|
| timestamp | value | `max_roll_over = 0` | explanation | `max_roll_over = 1` | explanation |
|-----------|-------|---------------------|-------------|---------------------|-------------|
| 0 | 0.0 |
| 2 | 2.0 |
| 4 | 4.0 |
| 6 | 6.0 |
||| 1.0 | 1.0 |
| 7 | | 0.8571... | (6-0) / (7-0) | 0.8571... | (6-0) / (7-0)
| 8 | 8.0 |
| 10 | 10.0 |
| 12 | 8.0 |
||| 0.0 | 0.33... |
| 14 | 6.0 |
| 14 | 8.0 | 0.0 | (8-8) / (14-7) | 0.2857... | (8-6) / (14-7)
| 16 | 4.0 |
| 18 | 2.0 |
| 20 | 0.0 |
||| -1.0 | -1.0 |

The difference stems from the change of the value between periods, e.g. from 6.0
to 8.0 between first and second period. Thoses changes are omitted with
to 8.0 between first and second period. Those changes are omitted with
`max_roll_over = 0` but are respected with `max_roll_over = 1`. That there are
no more differences in the calculated derivatives is due to the example data,
which has constant derivatives in during the first and last period, even when
Expand Down