Querying & Visualization Flashcards

What does the `rate()` function calculate when applied to a counter metric?

Answer: The per-second average rate of increase over the range window

`rate()` calculates the per-second average rate of increase of a counter over the specified time range window.

What is the key difference between `irate()` and `rate()` in PromQL?

Answer: `irate()` uses only the last two data points while `rate()` averages across the full range

`irate()` calculates the instantaneous rate using only the last two samples in the range, making it more responsive to sudden spikes than `rate()`.

What does the `increase()` function return for a counter over a given range vector?

Answer: The total increase in the counter value over the time range

`increase()` returns the total increase in a counter's value over the specified range, accounting for counter resets.

Which label matcher in PromQL uses a regular expression to match label values?

Answer: `=~`

The `=~` matcher selects labels matching a provided regular expression, while `!~` selects labels that do NOT match the regex.

What does `absent(up{job="myapp"})` return when the time series EXISTS?

Answer: An empty vector (no data)

`absent()` returns an empty vector when the input time series exists, and returns a vector with value 1 only when the series is missing.

What result type does the expression `http_requests_total[5m]` produce?

Answer: Range vector

Using a duration in square brackets creates a range vector, which contains a set of time series with a range of data points over the specified time window.

Which PromQL function would you use to predict a gauge's value 1 hour from now based on recent trends?

Answer: `predict_linear()`

`predict_linear(v range-vector, t scalar)` predicts the value t seconds from now using linear regression on the range vector.