prometheus/storage/remote/ewma.go

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// Copyright 2013 The Prometheus Authors
// 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 remote
import (
"sync"
"time"
"go.uber.org/atomic"
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)
// ewmaRate tracks an exponentially weighted moving average of a per-second rate.
type ewmaRate struct {
newEvents atomic.Int64
alpha float64
interval time.Duration
lastRate float64
init bool
mutex sync.Mutex
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}
// newEWMARate always allocates a new ewmaRate, as this guarantees the atomically
// accessed int64 will be aligned on ARM. See prometheus#2666.
func newEWMARate(alpha float64, interval time.Duration) *ewmaRate {
return &ewmaRate{
alpha: alpha,
interval: interval,
}
}
// rate returns the per-second rate.
func (r *ewmaRate) rate() float64 {
r.mutex.Lock()
defer r.mutex.Unlock()
return r.lastRate
}
// tick assumes to be called every r.interval.
func (r *ewmaRate) tick() {
newEvents := r.newEvents.Swap(0)
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instantRate := float64(newEvents) / r.interval.Seconds()
r.mutex.Lock()
defer r.mutex.Unlock()
switch {
case r.init:
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r.lastRate += r.alpha * (instantRate - r.lastRate)
case newEvents > 0:
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r.init = true
r.lastRate = instantRate
}
}
// inc counts one event.
func (r *ewmaRate) incr(incr int64) {
r.newEvents.Add(incr)
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}