PromQL Essentials: Practical Query Patterns

Calendar February 22, 2026
Observability
Intermediate
Promql-Query-Writing, Metric-Analysis, Recording-Rule-Design
Promql, Prometheus, Metrics, Monitoring, Queries, Recording-Rules
Prometheus, Grafana

Instant Vectors vs Range Vectors#

An instant vector returns one sample per time series at a single point in time. A range vector returns multiple samples per time series over a time window.

# Instant vector: current value of each series
http_requests_total{job="api"}

# Range vector: last 5 minutes of samples for each series
http_requests_total{job="api"}[5m]

You cannot graph a range vector directly. Functions like rate() and increase() consume a range vector and return an instant vector, which Grafana can then plot.

Advanced PromQL: Performance, Cardinality, and Complex Query Patterns

Calendar February 21, 2026
Observability
Advanced
Promql-Optimization, Cardinality-Management, Recording-Rule-Strategy, Sli-Query-Design
Promql, Prometheus, Cardinality, Recording-Rules, Performance, Metrics, Monitoring
Prometheus, Grafana, Promtool

Cardinality Explosion#

Cardinality is the number of unique time series Prometheus tracks. Every unique combination of metric name and label key-value pairs creates a separate series. A metric with 3 labels, each having 100 possible values, generates up to 1,000,000 series. In practice, cardinality explosions are the single most common way to kill a Prometheus instance.

The usual culprits are labels containing user IDs, request paths with embedded IDs (like /api/users/a]3f7b2c1), session tokens, trace IDs, or any unbounded value set. A seemingly innocent label like path on an HTTP metric becomes catastrophic when your API has RESTful routes with UUIDs in the path.

Prometheus Cardinality Management: Detecting, Preventing, and Reducing High-Cardinality Metrics

Calendar February 21, 2026
Observability
Advanced
Cardinality-Analysis, Metric-Relabeling, Recording-Rule-Design, Prometheus-Performance-Tuning
Prometheus, Cardinality, Time-Series, Relabeling, Recording-Rules, Performance, Tsdb, Labels
Prometheus, Grafana, Promtool

What Cardinality Means#

In Prometheus, cardinality is the number of unique time series. Every unique combination of metric name and label key-value pairs constitutes one series. The metric http_requests_total{method="GET", path="/api/users", status="200"} is one series. Change any label value and you get a different series. http_requests_total{method="POST", path="/api/users", status="201"} is a second series.

A single metric name can produce thousands or millions of series depending on its labels. A metric with no labels is exactly one series. A metric with one label that has 10 possible values is 10 series. A metric with three labels, each having 100 possible values, is up to 1,000,000 series (100 x 100 x 100), though in practice not every combination occurs.