Rust SDK — metrics
The Tell Rust SDK supports product analytics, structured logging, and now infrastructure metrics from a single dependency. Fast and lightweight — 80 ns per call, 10M events/sec delivered. Your thread serializes, encodes, and moves on while the background worker batches and ships over a persistent TCP connection.
API
Fire-and-forget, thread-safe, synchronous calls with async background delivery.
- Events —
track,identify,group,revenue,alias. User behavior, conversion, identity resolution - Logs — structured logging at any severity level with service tagging and typed payloads
- Metrics (new) — gauge, counter, histogram with typed labels and optional source tagging
// Events
client.track("user_123", "Page Viewed", props! { "url" => "/pricing" });
// Logs
client.log_error("connection refused", Some("db"), props! { "host" => "db.internal" });
// Metrics
client.gauge("cpu_percent", 72.5, &[("core", "0")]);
client.counter("http_requests", 1.0, &[("method", "GET"), ("status", "200")]);Metrics (new)
Monitor application performance and system resources from your Rust code. Three metric types, all at 30 ns per call with zero steady-state allocations.
- Gauge — point-in-time values: CPU percentage, memory usage, queue depth, active connections
- Counter — incremental counts: HTTP requests, errors, bytes processed. Delta by default, cumulative optional
- Histogram — full distributions with bucket boundaries, count, sum, min, max. Request latency at p50, p95, p99 without pre-aggregation
All three types support typed labels for breakdown by any dimension — endpoint, status code, host, region.
Disk-buffered delivery
Unsent data survives process restarts and network outages. The Witness server monitoring agent uses this to guarantee delivery across network failures and service restarts. Enable it in your own applications with one config line:
TellConfig::builder("your_api_key")
.buffer_path("/var/lib/myapp/tell-buffer")Batches are written to disk when the server is unreachable and drained on the next successful connection. Default buffer size is 64 MiB.