In the Prometheus Query Language (PromQL), aggregation functions such as maxovertime are designed to handle special float values like NaN (Not a Number) gracefully. When calculating the maximum value over a given time range, any NaN values within the data points are ignored. The function then operates on the remaining valid numeric values. In this case, the function discards NaN and computes the maximum of the remaining values (1, 1), which is 1.

A. It errors out.

PromQL functions are built to be resilient; they handle NaN values by ignoring them rather than terminating with an error.

C. NaN

NaN is not propagated as the result unless all values in the range vector are NaN. The function's purpose is to find the maximum of the valid numbers.

D. No

This is not a valid data type or output for a PromQL function that is expected to return a numeric value or a vector.

1. Prometheus Official Documentation, Querying, Functions: The documentation for overtime functions describes their role in aggregating data over a range. The behavior with special values is consistent with standard aggregation operators.

Source: Prometheus Authors. (n.d.). Querying functions. Prometheus Documentation. Retrieved from https://prometheus.io/docs/prometheus/latest/querying/functions/#aggregationovertime

Section: maxovertime(range-vector)

2. Prometheus Official Documentation, Querying, Operators: The documentation for aggregation operators, which share the same logic as overtime functions regarding NaN handling, explicitly states that NaN values are ignored.

Source: Prometheus Authors. (n.d.). Querying operators. Prometheus Documentation. Retrieved from https://prometheus.io/docs/prometheus/latest/querying/operators/#aggregation-operators

Section: Aggregation operators (max). The text notes: "Aggregate over dimensions of a vector. ... NaN is ignored." This principle applies to all aggregation-style functions.