Metric Collection & Data Modeling Flashcards

Which Prometheus metric type is best suited for tracking the number of currently active HTTP connections?

Answer: Gauge

Gauges represent values that can go up or down, making them ideal for measuring currently active connections.

In Prometheus, what does the `le` label represent in a histogram metric?

Answer: Less than or equal to bucket boundary

The `le` label in histograms denotes the upper inclusive bound ('less than or equal to') for each bucket.

A Prometheus scrape target returns a metric with timestamp older than the staleness window. What happens?

Answer: Prometheus stores the stale sample with a special NaN value

Prometheus marks stale samples with a special staleness NaN marker to signal that the time series is no longer active.

Which exposition format does Prometheus use by default when scraping targets?

Answer: Plain text exposition format

Prometheus defaults to the plain text exposition format (version 0.0.4) when scraping targets.

What is the purpose of the `_total` suffix convention in Prometheus counter metrics?

Answer: It is required by the OpenMetrics specification for counters

The OpenMetrics specification requires counters to use the `_total` suffix to clearly indicate they are monotonically increasing totals.

How does Prometheus handle a counter reset (e.g., after a process restart) when using `rate()`?

Answer: It automatically detects the reset and adjusts the calculation

`rate()` automatically detects counter resets by checking for decreases in value and corrects the calculation accordingly.

Which label naming practice should be avoided in Prometheus to prevent high cardinality issues?

Answer: Using user IDs or email addresses as label values

Using unbounded values like user IDs or email addresses as label values creates extremely high cardinality, degrading Prometheus performance.