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// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this
use std::cmp;
use std::collections::HashMap;
use once_cell::sync::OnceCell;
use serde::{Deserialize, Serialize};
use super::{Bucketing, Histogram};
/// Create the possible ranges in a linear distribution from `min` to `max` with
/// `bucket_count` buckets.
///
/// This algorithm calculates `bucket_count` number of buckets of equal sizes between `min` and `max`.
///
/// Bucket limits are the minimal bucket value.
/// That means values in a bucket `i` are `bucket[i] <= value < bucket[i+1]`.
/// It will always contain an underflow bucket (`< 1`).
fn linear_range(min: u64, max: u64, count: usize) -> Vec<u64> {
let mut ranges = Vec::with_capacity(count);
ranges.push(0);
let min = cmp::max(1, min);
let count = count as u64;
for i in 1..count {
let range = (min * (count - 1 - i) + max * (i - 1)) / (count - 2);
ranges.push(range);
}
ranges
}
/// A linear bucketing algorithm.
///
/// Buckets are pre-computed at instantiation with a linear distribution from `min` to `max`
/// and `bucket_count` buckets.
#[derive(Debug, Clone, Serialize, Deserialize, PartialEq, Eq)]
pub struct PrecomputedLinear {
// Don't serialize the (potentially large) array of ranges, instead compute them on first
// access.
#[serde(skip)]
pub(crate) bucket_ranges: OnceCell<Vec<u64>>,
pub(crate) min: u64,
pub(crate) max: u64,
pub(crate) bucket_count: usize,
}
impl Bucketing for PrecomputedLinear {
/// Get the bucket for the sample.
///
/// This uses a binary search to locate the index `i` of the bucket such that:
/// bucket[i] <= sample < bucket[i+1]
fn sample_to_bucket_minimum(&self, sample: u64) -> u64 {
let limit = match self.ranges().binary_search(&sample) {
// Found an exact match to fit it in
Ok(i) => i,
// Sorted it fits after the bucket's limit, therefore it fits into the previous bucket
Err(i) => i - 1,
};
self.ranges()[limit]
}
fn ranges(&self) -> &[u64] {
// Create the linear range on first access.
self.bucket_ranges
.get_or_init(|| linear_range(self.min, self.max, self.bucket_count))
}
}
impl Histogram<PrecomputedLinear> {
/// Creates a histogram with `bucket_count` linear buckets in the range `min` to `max`.
pub fn linear(min: u64, max: u64, bucket_count: usize) -> Histogram<PrecomputedLinear> {
Histogram {
values: HashMap::new(),
count: 0,
sum: 0,
bucketing: PrecomputedLinear {
bucket_ranges: OnceCell::new(),
min,
max,
bucket_count,
},
}
}
}
#[cfg(test)]
mod test {
use super::*;
const DEFAULT_BUCKET_COUNT: usize = 100;
const DEFAULT_RANGE_MIN: u64 = 0;
const DEFAULT_RANGE_MAX: u64 = 100;
#[test]
fn can_count() {
let mut hist = Histogram::linear(1, 500, 10);
assert!(hist.is_empty());
for i in 1..=10 {
hist.accumulate(i);
}
assert_eq!(10, hist.count());
assert_eq!(55, hist.sum());
}
#[test]
fn overflow_values_accumulate_in_the_last_bucket() {
let mut hist =
Histogram::linear(DEFAULT_RANGE_MIN, DEFAULT_RANGE_MAX, DEFAULT_BUCKET_COUNT);
hist.accumulate(DEFAULT_RANGE_MAX + 100);
assert_eq!(1, hist.values[&DEFAULT_RANGE_MAX]);
}
#[test]
fn short_linear_buckets_are_correct() {
let test_buckets = vec![0, 1, 2, 3, 4, 5, 6, 7, 8, 10];
assert_eq!(test_buckets, linear_range(1, 10, 10));
// There's always a zero bucket, so we increase the lower limit.
assert_eq!(test_buckets, linear_range(0, 10, 10));
}
#[test]
fn long_linear_buckets_are_correct() {
// Hand calculated values using current default range 0 - 60000 and bucket count of 100.
// NOTE: The final bucket, regardless of width, represents the overflow bucket to hold any
// values beyond the maximum (in this case the maximum is 60000)
let test_buckets = vec![
0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23,
24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45,
46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67,
68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89,
90, 91, 92, 93, 94, 95, 96, 97, 98, 100,
];
assert_eq!(
test_buckets,
linear_range(DEFAULT_RANGE_MIN, DEFAULT_RANGE_MAX, DEFAULT_BUCKET_COUNT)
);
}
#[test]
fn default_buckets_correctly_accumulate() {
let mut hist =
Histogram::linear(DEFAULT_RANGE_MIN, DEFAULT_RANGE_MAX, DEFAULT_BUCKET_COUNT);
for i in &[1, 10, 100, 1000, 10000] {
hist.accumulate(*i);
}
assert_eq!(11111, hist.sum());
assert_eq!(5, hist.count());
assert_eq!(None, hist.values.get(&0));
assert_eq!(1, hist.values[&1]);
assert_eq!(1, hist.values[&10]);
assert_eq!(3, hist.values[&100]);
}
#[test]
fn accumulate_large_numbers() {
let mut hist = Histogram::linear(1, 500, 10);
hist.accumulate(u64::MAX);
hist.accumulate(u64::MAX);
assert_eq!(2, hist.count());
// Saturate before overflowing
assert_eq!(u64::MAX, hist.sum());
assert_eq!(2, hist.values[&500]);
}
}