Integrate High Dynamic Range Histogram

Instead of computing the statistical summary manually this commit makes
use of the HDR Histogram.

Additionally, the mean(s) and standard deviations are insufficient when
determining the respones behavior. Therefore, this commit also
introduces the output of the 99.x'th percentiles.

Cargo.toml

@@ -25,6 +25,7 @@ futures = "0.3.5"
 lazy_static = "1.4.0"
 num_cpus = "1.13.0"
 rand = "0.7.3"
+hdrhistogram = "7.4.0"
 
 # Add openssl-sys as a direct dependency so it can be cross compiled to
 # x86_64-unknown-linux-musl using the "vendored" feature below

src/main.rs

@@ -11,6 +11,7 @@ use crate::actions::Report;
 use clap::crate_version;
 use clap::{App, Arg};
 use colored::*;
+use hdrhistogram::Histogram;
 use linked_hash_map::LinkedHashMap;
 use std::collections::HashMap;
 use std::process;
@@ -63,34 +64,35 @@ struct DrillStats {
   total_requests: usize,
   successful_requests: usize,
   failed_requests: usize,
-  mean_duration: f64,
-  median_duration: f64,
-  stdev_duration: f64,
+  hist: Histogram<u64>,
+}
+
+impl DrillStats {
+  fn mean_duration(&self) -> f64 {
+    self.hist.mean() / 1_000.0
+  }
+  fn median_duration(&self) -> f64 {
+    self.hist.value_at_quantile(0.5) as f64 / 1_000.0
+  }
+  fn stdev_duration(&self) -> f64 {
+    self.hist.stdev() / 1_000.0
+  }
+  fn value_at_quantile(&self, quantile: f64) -> f64 {
+    self.hist.value_at_quantile(quantile) as f64 / 1_000.0
+  }
 }
 
 fn compute_stats(sub_reports: &[Report]) -> DrillStats {
+  let mut hist = Histogram::<u64>::new_with_bounds(1, 60 * 60 * 1000, 2).unwrap();
   let mut group_by_status = HashMap::new();
 
   for req in sub_reports {
     group_by_status.entry(req.status / 100).or_insert_with(Vec::new).push(req);
   }
 
-  let mut durations = sub_reports.iter().map(|r| r.duration).collect::<Vec<f64>>();
-  let mean_duration = durations.iter().fold(0f64, |a, &b| a + b) / durations.len() as f64;
-  let deviations = durations.iter().map(|a| (mean_duration - a).powf(2.0)).collect::<Vec<f64>>();
-  let stdev_duration = (deviations.iter().fold(0f64, |a, &b| a + b) / durations.len() as f64).sqrt();
-
-  durations.sort_by(|a, b| a.partial_cmp(b).unwrap());
-  let durlen = durations.len();
-  let median_duration = if durlen == 0 {
-    f64::NAN
-  } else if durlen % 2 == 0 {
-    durations[durlen / 2]
-  } else if durlen > 1 {
-    (durations[durlen / 2] + durations[durlen / 2 + 1]) / 2f64
-  } else {
-    durations[0]
-  };
+  for r in sub_reports.iter() {
+    hist += (r.duration * 1_000.0) as u64;
+  }
 
   let total_requests = sub_reports.len();
   let successful_requests = group_by_status.entry(2).or_insert_with(Vec::new).len();
@@ -100,9 +102,7 @@ fn compute_stats(sub_reports: &[Report]) -> DrillStats {
     total_requests,
     successful_requests,
     failed_requests,
-    mean_duration,
-    median_duration,
-    stdev_duration,
+    hist,
   }
 }
 
@@ -132,9 +132,12 @@ fn show_stats(list_reports: &[Vec<Report>], stats_option: bool, nanosec: bool, d
     println!("{:width$} {:width2$} {}", name.green(), "Total requests".yellow(), substats.total_requests.to_string().purple(), width = 25, width2 = 25);
     println!("{:width$} {:width2$} {}", name.green(), "Successful requests".yellow(), substats.successful_requests.to_string().purple(), width = 25, width2 = 25);
     println!("{:width$} {:width2$} {}", name.green(), "Failed requests".yellow(), substats.failed_requests.to_string().purple(), width = 25, width2 = 25);
-    println!("{:width$} {:width2$} {}", name.green(), "Median time per request".yellow(), format_time(substats.median_duration, nanosec).purple(), width = 25, width2 = 25);
-    println!("{:width$} {:width2$} {}", name.green(), "Average time per request".yellow(), format_time(substats.mean_duration, nanosec).purple(), width = 25, width2 = 25);
-    println!("{:width$} {:width2$} {}", name.green(), "Sample standard deviation".yellow(), format_time(substats.stdev_duration, nanosec).purple(), width = 25, width2 = 25);
+    println!("{:width$} {:width2$} {}", name.green(), "Median time per request".yellow(), format_time(substats.median_duration(), nanosec).purple(), width = 25, width2 = 25);
+    println!("{:width$} {:width2$} {}", name.green(), "Average time per request".yellow(), format_time(substats.mean_duration(), nanosec).purple(), width = 25, width2 = 25);
+    println!("{:width$} {:width2$} {}", name.green(), "Sample standard deviation".yellow(), format_time(substats.stdev_duration(), nanosec).purple(), width = 25, width2 = 25);
+    println!("{:width$} {:width2$} {}", name.green(), "99.0'th percentile".yellow(), format_time(substats.value_at_quantile(0.99), nanosec).purple(), width = 25, width2 = 25);
+    println!("{:width$} {:width2$} {}", name.green(), "99.5'th percentile".yellow(), format_time(substats.value_at_quantile(0.995), nanosec).purple(), width = 25, width2 = 25);
+    println!("{:width$} {:width2$} {}", name.green(), "99.9'th percentile".yellow(), format_time(substats.value_at_quantile(0.999), nanosec).purple(), width = 25, width2 = 25);
   }
 
   // compute global stats
@@ -148,9 +151,12 @@ fn show_stats(list_reports: &[Vec<Report>], stats_option: bool, nanosec: bool, d
   println!("{:width2$} {}", "Successful requests".yellow(), global_stats.successful_requests.to_string().purple(), width2 = 25);
   println!("{:width2$} {}", "Failed requests".yellow(), global_stats.failed_requests.to_string().purple(), width2 = 25);
   println!("{:width2$} {} {}", "Requests per second".yellow(), format!("{:.2}", requests_per_second).purple(), "[#/sec]".purple(), width2 = 25);
-  println!("{:width2$} {}", "Median time per request".yellow(), format_time(global_stats.median_duration, nanosec).purple(), width2 = 25);
-  println!("{:width2$} {}", "Average time per request".yellow(), format_time(global_stats.mean_duration, nanosec).purple(), width2 = 25);
-  println!("{:width2$} {}", "Sample standard deviation".yellow(), format_time(global_stats.stdev_duration, nanosec).purple(), width2 = 25);
+  println!("{:width2$} {}", "Median time per request".yellow(), format_time(global_stats.median_duration(), nanosec).purple(), width2 = 25);
+  println!("{:width2$} {}", "Average time per request".yellow(), format_time(global_stats.mean_duration(), nanosec).purple(), width2 = 25);
+  println!("{:width2$} {}", "Sample standard deviation".yellow(), format_time(global_stats.stdev_duration(), nanosec).purple(), width2 = 25);
+  println!("{:width2$} {}", "99.0'th percentile".yellow(), format_time(global_stats.value_at_quantile(0.99), nanosec).purple(), width2 = 25);
+  println!("{:width2$} {}", "99.5'th percentile".yellow(), format_time(global_stats.value_at_quantile(0.995), nanosec).purple(), width2 = 25);
+  println!("{:width2$} {}", "99.9'th percentile".yellow(), format_time(global_stats.value_at_quantile(0.999), nanosec).purple(), width2 = 25);
 }
 
 fn compare_benchmark(list_reports: &[Vec<Report>], compare_path_option: Option<&str>, threshold_option: Option<&str>) {