PCA Promql Practice Test 3 — 15 Questions

Question 1

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 2

Which THREE of the following modifiers or keywords are used in PromQL binary vector matching? (Choose THREE)

Accepted Answer

group_left. Binary vector matching modifiers include on, ignoring, group_left, and group_right.

Answer

keep_matching

Answer

group_by

Question 3

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 4

An operator writes a query to calculate error percentage: sum(rate(errors[5m])) / sum(rate(total[5m])) * 100. What happens if the denominator evaluates to zero or has no matching time series?

Accepted Answer

The query returns an empty vector (no data points).. Division by zero or division by an empty vector in PromQL results in an empty vector output.

Answer

Prometheus throws a fatal query evaluation runtime exception.

Answer

The query returns NaN for all series.

Answer

The query automatically returns infinity.

Question 5

What is the purpose of the instant vector selector syntax http_requests_total{job="api-server"}?

Accepted Answer

It selects current values of time series matching the metric name and label filter.. It selects the current value of all time series for the metric http_requests_total that have the label job set to api-server.

Answer

It aggregates all API server requests into a single sum.

Answer

It triggers an alert if the job is down.

Answer

It selects historical data points spanning the last hour for the matching series.

Question 6

Which function should be used to smooth out short-term fluctuations in a gauge metric by calculating the rolling average over a 10-minute window?

Accepted Answer

avg_over_time(node_load1[10m]). The avg_over_time() function calculates the average value of all data points in the specified range vector for each time series.

Answer

rate(node_load1[10m])

Answer

smooth(node_load1, 10m)

Answer

avg(node_load1[10m])

Question 7

You are troubleshooting a query and notice that label_replace is being used. What is the primary function of label_replace(v, dst_label, replacement, src_label, regex)?

Accepted Answer

It matches a regex against a source label value and writes the result into a destination label.. The label_replace function matches the regex against the value of src_label, and if it matches, sets dst_label to the replacement string.

Answer

It renames the Prometheus server instance in federated environments.

Answer

It drops all time series that do not contain the specified source label.

Answer

It replaces the metric name with a new string.

Question 8

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 9

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 10

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

Accepted Answer

unless. PromQL supports three set operators: and (intersection), unless (complement), and or (union).

Answer

intersect

Answer

union

Question 11

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 (+)

Answer

All arithmetic operators share equal precedence.

Answer

Multiplication (*)

Question 12

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.. Native histograms store multiple buckets within a single chunk/sample, reducing storage overhead and allowing dynamic bucket resolutions.

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 13

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 14

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 15

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])