metrics: add minor fixes to LFHistogram refactor

Implement median, fix percentiles.
Fix Snapshot visibility.

scylla/src/lib.rs

@@ -287,4 +287,4 @@ pub use transport::retry_policy;
 pub use transport::speculative_execution;
 
 #[cfg(feature = "metrics")]
-pub use transport::metrics::{Metrics, MetricsError};
+pub use transport::metrics::{Metrics, MetricsError, Snapshot};

scylla/src/transport/metrics.rs

@@ -119,20 +119,20 @@ impl Metrics {
 
         let (min, max) = Self::minmax(h.clone())?;
 
-        let percentile_args = [0.75, 0.9, 0.95, 0.99, 0.999];
+        let percentile_args = [50.0, 75.0, 90.0, 95.0, 99.0, 99.9];
         let percentiles = Self::percentiles(&h, &percentile_args)?;
 
         Ok(Snapshot {
             min,
             max,
             mean: Self::mean(h.clone())?,
-            stddev: Self::stddev(h.clone())?,
-            median: Self::median(h)?,
-            percentile_75: percentiles[0],
-            percentile_90: percentiles[1],
-            percentile_95: percentiles[2],
-            percentile_99: percentiles[3],
-            percentile_99_9: percentiles[4],
+            stddev: Self::stddev(h)?,
+            median: percentiles[0],
+            percentile_75: percentiles[1],
+            percentile_90: percentiles[2],
+            percentile_95: percentiles[3],
+            percentile_99: percentiles[4],
+            percentile_99_9: percentiles[5],
         })
     }
 
@@ -181,11 +181,6 @@ impl Metrics {
         }
     }
 
-    fn median(h: Histogram) -> Result<u64, MetricsError> {
-        // TODO: get the real median by iterating through the buckets.
-        Ok(0)
-    }
-
     fn percentiles(h: &Histogram, percentiles: &[f64]) -> Result<Vec<u64>, MetricsError> {
         let res = h.percentiles(percentiles)?;
         if let Some(ps) = res {
@@ -218,7 +213,7 @@ impl Metrics {
     fn minmax(h: Histogram) -> Result<(u64, u64), MetricsError> {
         let mut min = u64::MAX;
         let mut max = 0;
-        for bucket in h.clone().into_iter() {
+        for bucket in h.into_iter() {
             if bucket.count() == 0 {
                 continue;
             }