forked from TrueCloudLab/restic
130 lines
3.3 KiB
Go
130 lines
3.3 KiB
Go
// Copyright 2017, OpenCensus Authors
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package trace
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import (
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"time"
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)
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// samplePeriod is the minimum time between accepting spans in a single bucket.
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const samplePeriod = time.Second
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// defaultLatencies contains the default latency bucket bounds.
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// TODO: consider defaults, make configurable
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var defaultLatencies = [...]time.Duration{
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10 * time.Microsecond,
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100 * time.Microsecond,
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time.Millisecond,
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10 * time.Millisecond,
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100 * time.Millisecond,
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time.Second,
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10 * time.Second,
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time.Minute,
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}
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// bucket is a container for a set of spans for a particular error code or latency range.
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type bucket struct {
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nextTime time.Time // next time we can accept a span
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buffer []*SpanData // circular buffer of spans
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nextIndex int // location next SpanData should be placed in buffer
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overflow bool // whether the circular buffer has wrapped around
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}
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func makeBucket(bufferSize int) bucket {
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return bucket{
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buffer: make([]*SpanData, bufferSize),
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}
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}
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// add adds a span to the bucket, if nextTime has been reached.
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func (b *bucket) add(s *SpanData) {
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if s.EndTime.Before(b.nextTime) {
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return
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}
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if len(b.buffer) == 0 {
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return
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}
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b.nextTime = s.EndTime.Add(samplePeriod)
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b.buffer[b.nextIndex] = s
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b.nextIndex++
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if b.nextIndex == len(b.buffer) {
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b.nextIndex = 0
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b.overflow = true
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}
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}
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// size returns the number of spans in the bucket.
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func (b *bucket) size() int {
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if b.overflow {
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return len(b.buffer)
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}
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return b.nextIndex
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}
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// span returns the ith span in the bucket.
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func (b *bucket) span(i int) *SpanData {
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if !b.overflow {
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return b.buffer[i]
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}
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if i < len(b.buffer)-b.nextIndex {
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return b.buffer[b.nextIndex+i]
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}
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return b.buffer[b.nextIndex+i-len(b.buffer)]
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}
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// resize changes the size of the bucket to n, keeping up to n existing spans.
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func (b *bucket) resize(n int) {
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cur := b.size()
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newBuffer := make([]*SpanData, n)
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if cur < n {
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for i := 0; i < cur; i++ {
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newBuffer[i] = b.span(i)
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}
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b.buffer = newBuffer
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b.nextIndex = cur
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b.overflow = false
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return
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}
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for i := 0; i < n; i++ {
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newBuffer[i] = b.span(i + cur - n)
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}
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b.buffer = newBuffer
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b.nextIndex = 0
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b.overflow = true
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}
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// latencyBucket returns the appropriate bucket number for a given latency.
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func latencyBucket(latency time.Duration) int {
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i := 0
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for i < len(defaultLatencies) && latency >= defaultLatencies[i] {
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i++
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}
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return i
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}
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// latencyBucketBounds returns the lower and upper bounds for a latency bucket
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// number.
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//
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// The lower bound is inclusive, the upper bound is exclusive (except for the
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// last bucket.)
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func latencyBucketBounds(index int) (lower time.Duration, upper time.Duration) {
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if index == 0 {
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return 0, defaultLatencies[index]
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}
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if index == len(defaultLatencies) {
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return defaultLatencies[index-1], 1<<63 - 1
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}
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return defaultLatencies[index-1], defaultLatencies[index]
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}
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