Crate skeg_telemetry 

Zero-overhead telemetry for skeg.

All public API entry points are #[inline(always)]. When neither the stats nor http feature is enabled, every call collapses to a no-op the compiler eliminates (verified with cargo asm).

When stats is enabled (default), the static counters and histograms tick on the hot path with a single atomic fetch_add each. Reading the values is done by stats::dump_text (or the helper accessors on metrics / histograms); reading does not lock, and never blocks the hot path.

When http is also enabled, [http::serve_blocking] runs a tiny HTTP server on a dedicated thread that serves /metrics in Prometheus text format. The server is purely a reader — it never writes through the hot path.

Hot-path cost budget

• per-op counter tick: AtomicU64::fetch_add(1, Relaxed) ≈ 1–2 ns
• per-op histogram tick: leading-zeros bucket pick + one fetch_add ≈ 3–5 ns

The crate’s benches/overhead.rs gates these with criterion; CI fails the build if any record path exceeds 50 ns.

Re-exports

pub use dynamic::DynHistogram;

pub use dynamic::DynOp;

pub use dynamic::register_counter;

pub use dynamic::register_gauge;

pub use dynamic::register_histogram;

pub use metrics::MAX_SHARDS;

Modules

dynamic

Dynamic metric registry — extensibility without giving up zero overhead.

histograms

Fixed-bucket exponential histograms.

metrics

Static atomic metric storage.

stats

In-process text dumper for the RESP3 STATS command.

Macros

register_op

Register a DynOp (sharded counter + histogram) from a single base name. Expands at compile time to two calls into the dynamic registries with the canonical Prometheus suffixes.

Enums

Counter

Counters that exist outside the per-op hot path.

Gauge

Gauges (current value, not monotonic).

Op

Enumeration of operations tracked on the hot path.

Functions

add_counter

Add a delta to a counter (for batch / amortised paths).

decr_gauge

Decrement a gauge by one. Safe to call when the gauge is already zero (wraps; pair calls correctly with incr_gauge for symmetry).

incr_gauge

Increment a gauge by one. Pair with decr_gauge for “in flight” counters where the natural API is incr at the start of an operation and decr at the end.

record_op

Record completion of one operation, with its observed duration.

set_gauge

Set the current value of a gauge metric (overwrites; not a counter).

tick_counter

Increment a counter that is not tied to a specific operation.