PCA Promql Practice Test 4 — 15 Questions

Question 1

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 2

You are joining an instant vector of application metrics with a static configuration instant vector containing target metadata using 'on(instance) group_right'. What does the 'group_right' modifier achieve?

Accepted Answer

It allows the right-hand side to provide more time series than the left-hand side, keeping all right-hand side series and including matched left-hand side data.. In a many-to-one or one-to-many match, group_right causes the metric on the right-hand side to be included for every matching left-hand side, keeping all labels from the right side and supplementing them.

Answer

It reverses the vector matching direction to evaluate from right to left.

Answer

It drops all labels from the left-hand side vector.

Answer

It ensures that the output contains only time series found exclusively on the right side.

Question 3

You need to calculate the 99th percentile of request latency across all instances using a Prometheus histogram metric 'http_request_duration_seconds_bucket'. Which function and setup is correct?

Accepted Answer

histogram_quantile(0.99, rate(http_request_duration_seconds_bucket[5m])). The histogram_quantile() function calculates the $\phi$-quantile from the buckets of a histogram metric. It requires the bucket metric and the quantile as arguments.

Answer

histogram_quantile(http_request_duration_seconds_bucket[5m], 0.99)

Answer

quantile_over_time(0.99, http_request_duration_seconds_bucket[5m])

Answer

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

Question 4

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 5

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 6

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 7

Which of the following selectors matches metric names that start with 'http_'?

Accepted Answer

{__name__=~"http_.*"}. The regex matcher '=~' is used with regular expressions, and '^' anchors the match to the beginning of the string.

Answer

http_*(5m)

Answer

{metric=~"http_.*"}

Answer

{__name__="http_*"}

Question 8

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 9

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 10

You need to calculate the ratio of successful HTTP requests (status 200) to total HTTP requests. Both metrics are counters named 'http_requests_total'. How do you construct this query to ensure proper label matching between status='200' and total requests?

Accepted Answer

http_requests_total{status="200"} / ignoring(status) http_requests_total. To divide two vectors with different label sets (e.g., status='200' vs all statuses), you must use binary matching modifiers like 'ignoring(status)' or 'on'.

Answer

rate(http_requests_total{status="200"}[5m]) / rate(http_requests_total[5m]) ignoring(status)

Answer

sum(http_requests_total{status="200"}) / sum(http_requests_total)

Answer

http_requests_total{status="200"} / http_requests_total

Question 11

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.

Answer

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

Answer

The minimum scrape interval of the target exporter.

Question 12

You are using the 'predict_linear()' function to forecast disk space exhaustion based on the metric 'node_filesystem_free_bytes'. What type of input data does predict_linear require?

Accepted Answer

A range vector of gauge values and a time duration scalar.. predict_linear predicts the value of a gauge metric 't' seconds into the future based on a range vector using linear regression.

Answer

An instant vector representing current disk space.

Answer

Two instant vectors joined via an 'on' clause.

Answer

A counter range vector wrapped in a rate() function.

Question 13

You want to find the top 3 jobs with the highest CPU usage using the metric 'process_cpu_seconds_total'. Which PromQL query structure is correct?

Accepted Answer

topk(3, rate(process_cpu_seconds_total[5m])). The topk() function takes an integer 'k' and an instant vector (typically wrapped in rate()), returning the top k time series with the highest values.

Answer

bottomk(3, rate(process_cpu_seconds_total[5m]))

Answer

topk(3, process_cpu_seconds_total[5m])

Answer

topk(rate(process_cpu_seconds_total[5m]), 3)

Question 14

Which TWO of the following are valid data types returned by PromQL queries? (Choose two)

Accepted Answer

Range vector. PromQL queries evaluate to one of four types: instant vector, range vector, scalar, or string.

Answer

Histogram matrix

Answer

Log stream

Answer

Distributed trace

Question 15

Which TWO of the following label matching operators are supported in Prometheus label selectors? (Choose two)

Accepted Answer

= (exact equality). Prometheus supports '=' (exact match), '!=' (exact mismatch), '=~' (regex match), and '!~' (regex mismatch).

Answer

#= (wildcard match)

Answer

== (boolean equality comparison)

Answer

:= (assignment and match)