PCA Promql Practice Test 4 — 15 Questions

Question 1

When evaluating a histogram metric, what does the special pseudo-label le represent in bucket time series?

Accepted Answer

The upper bound of the cumulative histogram bucket.. The le (less than or equal to) label represents the upper bound of a histogram bucket.

Answer

The linear extrapolation factor for summary metrics.

Answer

The logging event identifier for tracing.

Answer

The exact latency error margin of the measurement.

Question 2

An operator needs to find the rate of change of a counter using deriv(). Why is this considered a bad practice in Prometheus?

Accepted Answer

deriv() does not account for counter resets, causing massive negative drops when counters reset.. deriv() is designed for linear regression on gauge metrics over range vectors and does not handle counter resets, leading to incorrect downward spikes when counters reset.

Answer

deriv() automatically multiplies output by an undocumented scaling factor.

Answer

deriv() requires native histograms, which are incompatible with standard counters.

Answer

deriv() only works with scalar values and rejects time series vectors.

Question 3

Which THREE of the following are valid set operators in PromQL for combining instant vectors? (Choose THREE)

Accepted Answer

unless. In PromQL, the set operators available for combining instant vectors are `and`, `or`, and `unless`. Option D (`and`) is correct because it returns the elements of the left-hand vector that also exist in the right-hand vector, matching on labels. Option E (`or`) is correct because it returns all elements of the left-hand vector plus any elements from the right-hand vector that do not have matching label sets on the left. Option C (`unless`) is correct because it returns elements of the left-hand vector that do not have matching label sets in the right-hand vector. Options A (`intersect`) and B (`union`) are not valid PromQL set operators; the intersection behavior is expressed by `and`, and union-like behavior is expressed by `or`, so neither keyword exists in the language.

Answer

intersect

Answer

union

Question 4

Which operator has higher precedence in PromQL: exponential (^), multiplication (*), or addition (+)?

Accepted Answer

Exponentiation (^). Exponentiation has the highest precedence in PromQL, followed by multiplication/division, and then addition/subtraction.

Answer

Addition (+)

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All arithmetic operators share equal precedence.

Answer

Multiplication (*)

Question 5

Which TWO of the following statements regarding native histograms in Prometheus are correct? (Choose TWO)

Accepted Answer

The histogram_quantile() function can evaluate native histograms directly.. Option B is correct because Prometheus's histogram_quantile() function natively supports native histograms, computing quantiles directly from the stored bucket distribution without needing the classic le-label bucket series. Option C is correct because native histograms encode the entire bucket distribution (counts across dynamically determined buckets) inside a single time series sample, rather than exposing one series per bucket as classic histograms do. Options A, D, and E are incorrect: native histograms use automatically configured, dynamic bucket boundaries so users do not pre-define explicit buckets; they work fine with rate-related PromQL functions like rate() and increase(); and they do not simply double memory consumption of counters, since their overhead depends on bucket count and schema resolution.

Answer

Native histograms require users to manually pre-define explicit bucket boundaries in application code.

Answer

Native histograms are incompatible with all rate-related PromQL functions.

Answer

Native histograms double the memory consumption of traditional counters.

Question 6

A Prometheus administrator wants to query the current value of the metric 'http_requests_total'. Which of the following PromQL expressions should be used?

Accepted Answer

http_requests_total. The expression `http_requests_total` is a valid PromQL instant vector selector that returns the current value of the metric at the evaluation timestamp. It does not require a range or function because the question asks for the current value, not a rate or aggregation. This is the simplest and correct way to query a single metric's latest sample.

Answer

http_requests_total[5m]

Answer

rate(http_requests_total)

Answer

sum(http_requests_total) over (instance)

Question 7

Which PromQL function is specifically designed to calculate the per-second average rate of increase of a time series over a given range vector?

Accepted Answer

rate(). The rate() function in PromQL is specifically designed to calculate the per-second average rate of increase of a time series over a given range vector. It takes a range vector (e.g., http_requests_total[5m]) and returns the average per-second growth rate, handling counter resets automatically. This is the canonical function for computing rates of counters.

Answer

deriv()

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irate()

Answer

increase()

Question 8

You are monitoring a counter metric 'errors_total' and need to calculate the total number of errors that occurred over the last 1 hour. Which function is most appropriate?

Accepted Answer

increase(errors_total[1h]). The increase() function returns the total increase in the time series over the specified range vector, properly accounting for counter resets.

Answer

rate(errors_total[1h])

Answer

sum(errors_total[1h])

Answer

delta(errors_total[1h])

Question 9

When evaluating a PromQL query involving arithmetic operators, such as 'vector1 + vector2 * vector3', which operator has the highest precedence?

Accepted Answer

* (Multiplication). In PromQL, arithmetic operators follow standard mathematical precedence: multiplication (*), division (/), and modulo (%) bind tighter than addition (+) and subtraction (-). Therefore in 'vector1 + vector2 * vector3', the multiplication of vector2 and vector3 is evaluated first, and the result is then added to vector1. This mirrors conventional arithmetic rules rather than left-to-right evaluation.

Answer

Both have equal precedence and are evaluated left-to-right.

Answer

+ (Addition)

Answer

Precedence is determined by the order of labels.

Question 10

A Prometheus selector includes a negative regex match for environment names: 'environment!="staging"'. Which selector operator achieves this using regular expressions instead of exact matching?

Accepted Answer

environment!~"staging". The '!=' operator is for exact inequality, while '!~' is the negative regular expression match operator in PromQL.

Answer

environment!regex("staging")

Answer

environment!match("staging")

Answer

environment!="staging"

Question 11

When writing a PromQL query involving a vector and a scalar, such as 'node_memory_free_bytes / (1024 * 1024)', how does Prometheus handle label matching?

Accepted Answer

The scalar operation is applied to every time series value in the vector independently, preserving all labels.. Operations between an instant vector and a scalar are performed on each data point of the vector. Labels are unaffected.

Answer

The operation is only applied to the first time series returned by the vector selector.

Answer

The scalar is matched against labels of the vector using exact label equality.

Answer

The query fails because scalars cannot be combined with vectors without an explicit 'on' clause.

Question 12

You are joining two vectors where the left vector has labels {job="api", instance="host1"} and the right vector has labels {job="api", region="us-east"}. You use the query 'vector_a + ignoring(instance, region) vector_b'. What does the 'ignoring' modifier do?

Accepted Answer

It causes Prometheus to exclude the listed labels ('instance', 'region') from consideration during the equality check between the two vectors.. The `ignoring` modifier in PromQL vector matching tells Prometheus to ignore the specified labels when matching time series between the two vectors. In this case, `ignoring(instance, region)` means that the labels `instance` and `region` are not considered when finding matching pairs, so the left vector's `instance` and right vector's `region` are excluded from the equality check. This allows matching based on the remaining labels, such as `job`.

Answer

It replaces missing instance and region labels with default values.

Answer

It removes 'instance' and 'region' from the final output time series.

Answer

It hides errors caused by missing 'instance' or 'region' labels in the time series.

Question 13

What is the primary operational difference between the 'rate()' and 'irate()' functions in PromQL?

Accepted Answer

rate() averages the per-second rate over the entire specified range vector, while irate() calculates the rate based on the last two data points in the range vector.. rate() calculates the average per-second rate over the whole range vector, smoothing spikes, whereas irate() calculates the instantaneous rate using only the last two points.

Answer

rate() can be used with instant vectors, whereas irate() requires range vectors.

Answer

irate() automatically accounts for counter resets, whereas rate() does not.

Answer

irate() supports gauges, while rate() only supports counters.

Question 14

Which function would you use to find the maximum value of a gauge metric 'node_cpu_load' over the past 30 minutes?

Accepted Answer

max_over_time(node_cpu_load[30m]). The max_over_time() function calculates the maximum value of all data points in the specified range vector for each time series.

Answer

rate(node_cpu_load[30m])

Answer

max(node_cpu_load[30m])

Answer

topk(1, node_cpu_load[30m])

Question 15

When executing a subquery in PromQL, such as 'max_over_time(rate(http_request_total[5m])[30m:1m])', what does the resolution parameter ('1m') specify?

Accepted Answer

The evaluation step size at which the inner expression is run across the subquery window.. The resolution inside subquery brackets specifies the evaluation step size at which the inner expression is evaluated within the subquery range.

Answer

The smoothing factor applied to eliminate high-frequency noise.

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The time-to-live for cached subquery results in Prometheus storage.

Answer

The minimum scrape interval of the target exporter.