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houseme
633c131cef
The `metrics` macros re-run the recorder's `register_*` on every emission — a `RwLock` read, a name-key hash, and an `Arc` clone — even for a metric that never varies its key. For the hot, label-less recorders on the per-IO path (`record_data_transfer`, `record_io_latency`, `record_io_latency_p95/p99`, `record_io_queue_congestion`) that lookup is pure overhead once observability is on. Add `counter_increment_cached!` / `gauge_set_cached!` / `histogram_record_cached!` that resolve the handle once via `LazyLock` in production and reuse it. Under `cfg(test)` they re-resolve on every call, because the `metrics` crate resolves against a thread-local recorder that `with_local_recorder` swaps per test — a process-global cached handle would bind to whichever recorder was active first and break test capture. The macros only wrap FIXED (label-less) keys, and the `metrics_enabled()` gate still short-circuits before any emission when disabled. Verified: the only callers of these functions are the collector (io-metrics' own cfg(test) tests, which re-resolve) and production code; no cross-crate test captures them. rustfs-io-metrics builds on both cfg paths, 147 unit + 4 doctests pass, clippy clean. Addresses rustfs/backlog#1185 (P3, per-emission handle caching). Co-authored-by: heihutu <heihutu@gmail.com>