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// Copyright 2016 Google Inc. All Rights Reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package stat
import (
"bytes"
"encoding/csv"
"fmt"
"io"
"math"
"sort"
"strconv"
"text/tabwriter"
"time"
)
type byDuration []time.Duration
func (data byDuration) Len() int { return len(data) }
func (data byDuration) Swap(i, j int) { data[i], data[j] = data[j], data[i] }
func (data byDuration) Less(i, j int) bool { return data[i] < data[j] }
// quantile returns a value representing the kth of q quantiles.
// May alter the order of data.
func quantile(data []time.Duration, k, q int) (quantile time.Duration, ok bool) {
if len(data) < 1 {
return 0, false
}
if k > q {
return 0, false
}
if k < 0 || q < 1 {
return 0, false
}
sort.Sort(byDuration(data))
if k == 0 {
return data[0], true
}
if k == q {
return data[len(data)-1], true
}
bucketSize := float64(len(data)-1) / float64(q)
i := float64(k) * bucketSize
lower := int(math.Trunc(i))
var upper int
if i > float64(lower) && lower+1 < len(data) {
// If the quantile lies between two elements
upper = lower + 1
} else {
upper = lower
}
weightUpper := i - float64(lower)
weightLower := 1 - weightUpper
return time.Duration(weightLower*float64(data[lower]) + weightUpper*float64(data[upper])), true
}
type Aggregate struct {
Name string
Count, Errors int
Min, Median, Max time.Duration
P75, P90, P95, P99 time.Duration // percentiles
}
// NewAggregate constructs an aggregate from latencies. Returns nil if latencies does not contain aggregateable data.
func NewAggregate(name string, latencies []time.Duration, errorCount int) *Aggregate {
agg := Aggregate{Name: name, Count: len(latencies), Errors: errorCount}
if len(latencies) == 0 {
return nil
}
var ok bool
if agg.Min, ok = quantile(latencies, 0, 2); !ok {
return nil
}
if agg.Median, ok = quantile(latencies, 1, 2); !ok {
return nil
}
if agg.Max, ok = quantile(latencies, 2, 2); !ok {
return nil
}
if agg.P75, ok = quantile(latencies, 75, 100); !ok {
return nil
}
if agg.P90, ok = quantile(latencies, 90, 100); !ok {
return nil
}
if agg.P95, ok = quantile(latencies, 95, 100); !ok {
return nil
}
if agg.P99, ok = quantile(latencies, 99, 100); !ok {
return nil
}
return &agg
}
func (agg *Aggregate) String() string {
if agg == nil {
return "no data"
}
var buf bytes.Buffer
tw := tabwriter.NewWriter(&buf, 0, 0, 1, ' ', 0) // one-space padding
fmt.Fprintf(tw, "min:\t%v\nmedian:\t%v\nmax:\t%v\n95th percentile:\t%v\n99th percentile:\t%v\n",
agg.Min, agg.Median, agg.Max, agg.P95, agg.P99)
tw.Flush()
return buf.String()
}
// WriteCSV writes a csv file to the given Writer,
// with a header row and one row per aggregate.
func WriteCSV(aggs []*Aggregate, iow io.Writer) (err error) {
w := csv.NewWriter(iow)
defer func() {
w.Flush()
if err == nil {
err = w.Error()
}
}()
err = w.Write([]string{"name", "count", "errors", "min", "median", "max", "p75", "p90", "p95", "p99"})
if err != nil {
return err
}
for _, agg := range aggs {
err = w.Write([]string{
agg.Name, strconv.Itoa(agg.Count), strconv.Itoa(agg.Errors),
agg.Min.String(), agg.Median.String(), agg.Max.String(),
agg.P75.String(), agg.P90.String(), agg.P95.String(), agg.P99.String(),
})
if err != nil {
return err
}
}
return nil
}
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