PCA Practice Test 23 — 15 Questions

Question 1

Which THREE of the following are valid aggregation operators in PromQL? (Choose THREE)

Accepted Answer

stddev. PromQL provides numerous aggregation operators including sum, min, max, avg, stddev, stdvar, count, count_values, bottomk, topk, and quantile.

Answer

median

Answer

average

Question 2

What is the difference between 'count' and 'count_values'?

Accepted Answer

count returns the number of series; count_values returns the frequency of values.. count aggregates by number of series, while count_values counts the number of occurrences of each sample value.

Answer

count_values is faster.

Answer

count is for gauges; count_values is for counters.

Answer

There is no difference.

Question 3

An operator needs to query the current, un-extrapolated rate of increase per second over the last 5 minutes for a counter metric named http_requests_total. Which function should they use?

Accepted Answer

irate(http_requests_total[5m]). The irate() function calculates the per-second rate of increase of a time series based on the last two data points in the specified range window, making it ideal for volatile, high-frequency counters.

Answer

increase(http_requests_total[5m])

Answer

rate(http_requests_total[5m])

Answer

delta(http_requests_total[5m])

Question 4

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 5

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 6

Which aggregation operator would you use to calculate the total sum of a metric across all instances?

Accepted Answer

sum(). sum() is the standard operator for calculating totals across dimensions.

Answer

avg_over_time()

Answer

total()

Answer

count()

Question 7

Which operator has the highest precedence in PromQL?

Accepted Answer

Exponentiation (^). PromQL operator precedence follows standard mathematical rules: ^ > *, /, %, +, -.

Answer

Logical OR (or)

Answer

Addition (+)

Answer

Equality (==)

Question 8

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. An instant vector selector like 'http_requests_total' queries the current value (instant vector) of a metric. Range vectors require a duration in brackets.

Answer

http_requests_total[5m]

Answer

rate(http_requests_total)

Answer

sum(http_requests_total) over (instance)

Question 9

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 instructs Prometheus to ignore specified labels when conducting vector matching between two vectors.

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 10

Which TWO of the following conditions will cause the rate() function to return NaN or empty results? (Choose TWO)

Accepted Answer

The time series has no samples within the specified range window.. rate() requires range vectors with sufficient data points and valid counter metrics. Stale series or ranges with zero samples yield empty or NaN results.

Answer

The queried metric is a gauge rather than a counter, and samples do not follow monotonic rules.

Answer

The query is executed with an instant vector instead of a range vector.

Answer

The counter experienced a reset during the window.

Question 11

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

Accepted Answer

* (Multiplication). Multiplication (*) and division (/) have higher precedence than addition (+) and subtraction (-) in PromQL.

Answer

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

Answer

+ (Addition)

Answer

Precedence is determined by the order of labels.

Question 12

Which TWO of the following statements about 'rate' vs 'irate' are correct?

Accepted Answer

rate() is better for alerting on slow-moving counters.. rate is better for smooth graphs, irate is for high-precision local spikes.

Answer

irate() returns the average over the whole window.

Answer

irate() is better for long-term trends.

Answer

rate() only works on gauges.

Question 13

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 is designed for counters to calculate the per-second average rate of increase, handling counter resets automatically.

Answer

deriv()

Answer

irate()

Answer

increase()

Question 14

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 restricts vector matching to a specified list of labels.

Answer

group_left(...)

Answer

ignoring(...)

Answer

matching(...)

Question 15

How does Prometheus handle subqueries embedded within an instant query, such as rate(http_requests_total[5m])[30m:1m]?

Accepted Answer

It runs the inner instant query at multiple evaluation timestamps over the specified range at the given resolution, returning a range vector.. A subquery evaluates an instant query expression over a given range with a specified resolution at multiple points in time, returning a range vector.

Answer

It caches the inner query results in memory for 30 minutes.

Answer

It increases the global scrape interval to 1 minute for the next 30 minutes.

Answer

It converts the range vector into a scalar through statistical interpolation.