Which metric type uses the delta() function?

Thedelta()function in PromQL calculates thedifference between the first and last samplesin a range vector over a specified time window. This function is primarily used withgauge metrics, as they can move both up and down, and delta() captures that net change directly.

For example, if a gauge metric like node_memory_Active_bytes changes from 1000 to 1200 within a 5-minute window, delta(node_memory_Active_bytes[5m]) returns 200.

Unlike rate() or increase(), which are designed for monotonically increasing counters, delta() is ideal for metrics representing resource levels, capacities, or instantaneous measurements that fluctuate over time.