Expand description
Observability primitives: counters, gauges, histograms, plus the per-statement accumulator the engine uses to
attribute work to a query. The crate owns the metric registry, the in-memory storage of recent samples, and the
snapshot type external collectors read from. Metrics are addressed by MetricId so a single hierarchy can hold
shape-scoped, flow-node-scoped, and system-scoped values without colliding.
This crate produces the data; sub-metric is the subsystem that delivers it to an external sink. Anything that
emits a metric inside the engine writes here; downstream readers either iterate the snapshot directly (for
in-process use) or subscribe through sub-metric (for export).