PCA Promql Practice Test 2 — 15 Questions

Question 1

Which operator performs a logical 'not' on a comparison?

Accepted Answer

unless. The 'unless' set operator is used to filter out series that match the right-hand side.

Answer

!

Answer

not

Answer

none

Question 2

Which THREE of the following are valid time-range units in PromQL?

Accepted Answer

m. In PromQL, duration values appended to selectors and range vectors must use one of the supported time units: ms (milliseconds), s (seconds), m (minutes), h (hours), d (days), w (weeks), and y (years). Option B (m) is correct because m denotes minutes in PromQL durations, such as rate(http_requests_total[5m]). Option D (h) is correct because h denotes hours, e.g., [2h] for a two-hour range. Option E (s) is correct because s denotes seconds, e.g., [30s]. Options A (ns) and C (ms) are not both valid: ns (nanoseconds) is not a supported PromQL time unit, and although ms is valid, it is not marked as correct here, so it does not belong among the three selected answers.

Answer

ns

Answer

ms

Question 3

Which THREE of the following are valid ways to modify a binary operation join?

Accepted Answer

group_right. In LINQ, a binary operation join can be modified with group_right, on, and ignoring. Option A, group_right, is correct because it turns the join into a group join, producing a sequence of left elements each paired with matching right elements. Option B, on, is correct because it specifies the key selector expressions that determine how elements from the two sequences are matched. Option E, ignoring, is correct because it specifies a key comparer, such as StringComparer.OrdinalIgnoreCase, to control equality during the join. Option C, merge, is not a valid join modifier in LINQ, and option D, include, is not a valid join modifier either.

Answer

merge

Answer

include

Question 4

How does PromQL handle operator precedence between arithmetic operators like multiplication (*) and addition (+)?

Accepted Answer

Multiplication has higher precedence than addition.. PromQL follows standard mathematical order of operations, where multiplication and division take precedence over addition and subtraction.

Answer

Operators are evaluated strictly from left to right regardless of type.

Answer

Operators are evaluated strictly from right to left.

Answer

Addition has higher precedence than multiplication.

Question 5

Which selector syntax correctly matches all time series where the environment label does NOT equal production?

Accepted Answer

http_requests_total{environment!="production"}. The != operator is the standard negative equality matcher in PromQL label selectors.

Answer

http_requests_total{environment=~"^((?!production).)*$"}

Answer

http_requests_total{environment!~"production"}

Answer

http_requests_total{environment!^"production"}

Question 6

An administrator wants to aggregate CPU usage across all nodes, keeping the instance label while summing the values. Which aggregation clause should be used?

Accepted Answer

sum by (instance) (node_cpu_seconds_total). The by clause specifies the labels that should be preserved in the aggregated result vector.

Answer

sum(node_cpu_seconds_total) keeping (instance)

Answer

sum(node_cpu_seconds_total) group by (instance)

Answer

sum without (instance) (node_cpu_seconds_total)

Question 7

When performing a vector-to-vector binary operation between two instant vectors of different label sets, which modifier allows matching on a subset of common labels?

Accepted Answer

on(...). The 'on(...)' modifier in PromQL allows vector-to-vector binary operations to match on a specified subset of labels, ignoring all other labels. When two instant vectors have different label sets, 'on(label1, label2)' restricts matching to only those labels, enabling the operation to proceed. This is the correct modifier for matching on a subset of common labels.

Answer

group_left(...)

Answer

ignoring(...)

Answer

matching(...)

Question 8

A user executes an instant query for a metric without providing a range vector. What type of vector is returned by default?

Accepted Answer

Instant vector. An instant vector evaluates to a single data point per time series at the current evaluation timestamp.

Answer

String

Answer

Range vector

Answer

Scalar

Question 9

You need to calculate the 99th percentile HTTP request latency from a Prometheus histogram named http_request_duration_seconds. Which function is correct?

Accepted Answer

histogram_quantile(0.99, rate(http_request_duration_seconds_bucket[5m])). The correct PromQL expression is histogram_quantile(0.99, rate(http_request_duration_seconds_bucket[5m])). This computes the 99th percentile by first calculating the per-second rate of increase of each bucket over a 5-minute window, then applying histogram_quantile to interpolate the quantile from the bucket boundaries. The rate function is essential to convert cumulative counters into a rate suitable for quantile estimation.

Answer

rate(histogram_quantile(0.99, http_request_duration_seconds_bucket)[5m])

Answer

quantile_over_time(0.99, http_request_duration_seconds[5m])

Answer

histogram_quantile(http_request_duration_seconds_bucket[5m], 0.99)

Question 10

Which PromQL aggregator should be used to count the total number of active time series matching a selector?

Accepted Answer

count(up). The count operator counts the number of time series in an instant vector.

Answer

sum(up)

Answer

len(up)

Answer

total(up)

Question 11

A Prometheus alert expression uses rate(http_requests_total[5m]) > 10. During a service restart, counter resets occur. How does the rate() function account for these counter resets?

Accepted Answer

It assumes the counter reset to zero and adds the new value to the previous value.. The rate() function automatically detects decreases in counter values (resets) and adjusts the calculation assuming the counter restarted at zero.

Answer

It treats the negative difference as an error and returns 0 for the entire range.

Answer

It adds a fixed offset value configured in Prometheus global settings.

Answer

It drops the samples surrounding the reset, resulting in a null value for that evaluation.

Question 12

Which regular expression matcher selects all time series where the status label begins with the digit 5?

Accepted Answer

http_requests_total{status=~"^5.*"}. The =~ operator combined with a regular expression starting with ^5 matches labels beginning with 5.

Answer

http_requests_total{status=@"5*"}

Answer

http_requests_total{status=^"5"}

Answer

http_requests_total{status=~"5$"}

Question 13

You want to find the maximum value of a gauge metric across all instances over a 1-hour sliding window. Which function accomplishes this?

Accepted Answer

max_over_time(node_memory_usage_bytes[1h]). The max_over_time() function evaluates the maximum value of all data points in a specified range vector for each time series.

Answer

max(node_memory_usage_bytes[1h])

Answer

topk(1, node_memory_usage_bytes[1h])

Answer

max_with_range(node_memory_usage_bytes, 1h)

Question 14

What is the primary difference between an instant vector and a range vector in PromQL?

Accepted Answer

An instant vector contains a single sample per time series, while a range vector contains a set of samples over time.. Instant vectors contain a single sample per time series for the given timestamp, whereas range vectors contain a set of data points over a time window.

Answer

An instant vector includes timestamps from the future, while range vectors are strictly historical.

Answer

An instant vector can only be used with counters, while range vectors can only be used with gauges.

Answer

A range vector evaluates faster because it caches historical calculations.

Question 15

You need to calculate the per-second rate of increase of http_requests_total over a 1-minute window. Why is using a 1-minute range window generally discouraged in production?

Accepted Answer

It is too short relative to typical scrape intervals, leading to high noise and sensitivity to jitter.. Prometheus scrapes most targets every 15 seconds. A 1-minute window only contains about 4 data points, making the rate calculation highly sensitive to small scraping jitters.

Answer

It disables counter reset detection algorithms.

Answer

PromQL automatically rejects any range window shorter than 5 minutes.

Answer

It causes Prometheus to run out of memory due to high sample density.