Method record_wait

nodedb/src/data/io/io_metrics.rs:91–101

(&self, tier: usize, wait_ns: u64)

    /// `wait_ns` is elapsed nanoseconds from task-enqueue to read_files return.
    #[inline]
    pub fn record_wait(&self, tier: usize, wait_ns: u64) {
        self.count[tier].fetch_add(1, Ordering::Relaxed);
        self.sum_ns[tier].fetch_add(wait_ns, Ordering::Relaxed);
        for (i, &boundary) in IO_WAIT_BUCKETS_NS.iter().enumerate() {
            if wait_ns <= boundary {
                self.buckets[tier][i].fetch_add(1, Ordering::Relaxed);
                return;
            }
        }
        // Overflow: beyond all buckets — counted in `count` but no bucket.
    }

    /// Emit Prometheus text for all IO metrics.
    ///