In Prometheus, histogram metrics use cumulative buckets to record the count of observations that fall within specific duration thresholds. Each bucket has a label le (''less than or equal to''), representing the upper bound of that bucket.

In the given metric, the bucket labeled le='0.1' has a value of 1, meaning exactly one request took less than or equal to 0.1 seconds. Buckets are cumulative, so:

le='0.05' 0 requests 0.05 seconds

le='0.1' 1 request 0.1 seconds

le='1' 3 requests 1 second

le='+Inf' all 3 requests total

The _sum and _count values represent total duration and request count respectively, but the number of requests below a given threshold is read directly from the bucket's le value.

Verified from Prometheus documentation -- Understanding Histograms and Summaries, Bucket Semantics, and Histogram Query Examples sections.