github.com/unigraph-dev/dgraph@v1.1.1-0.20200923154953-8b52b426f765/x/histogram.go (about)

     1  // Copyright 2015 The Cockroach Authors.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
    12  // implied. See the License for the specific language governing
    13  // permissions and limitations under the License.
    14  
    15  package x
    16  
    17  import (
    18  	"sync"
    19  	"time"
    20  
    21  	"github.com/codahale/hdrhistogram"
    22  )
    23  
    24  const (
    25  	// The number of histograms to keep in rolling window.
    26  	histWrapNum = 2
    27  )
    28  
    29  // A slidingHistogram is a wrapper around an
    30  // hdrhistogram.WindowedHistogram. The caller must enforce proper
    31  // synchronization.
    32  type slidingHistogram struct {
    33  	windowed *hdrhistogram.WindowedHistogram
    34  	nextT    time.Time
    35  	duration time.Duration
    36  }
    37  
    38  // newSlidingHistogram creates a new windowed HDRHistogram with the given
    39  // parameters. Data is kept in the active window for approximately the given
    40  // duration. See the documentation for hdrhistogram.WindowedHistogram for
    41  // details.
    42  func newSlidingHistogram(duration time.Duration, maxVal int64, sigFigs int) *slidingHistogram {
    43  	if duration <= 0 {
    44  		panic("cannot create a sliding histogram with nonpositive duration")
    45  	}
    46  	return &slidingHistogram{
    47  		nextT:    time.Now(),
    48  		duration: duration,
    49  		windowed: hdrhistogram.NewWindowed(histWrapNum, 0, maxVal, sigFigs),
    50  	}
    51  }
    52  
    53  func (h *slidingHistogram) tick() {
    54  	h.nextT = h.nextT.Add(h.duration / histWrapNum)
    55  	h.windowed.Rotate()
    56  }
    57  
    58  func (h *slidingHistogram) nextTick() time.Time {
    59  	return h.nextT
    60  }
    61  
    62  func (h *slidingHistogram) Current() *hdrhistogram.Histogram {
    63  	for h.nextTick().Before(time.Now()) {
    64  		h.tick()
    65  	}
    66  	return h.windowed.Merge()
    67  }
    68  
    69  func (h *slidingHistogram) RecordValue(v int64) error {
    70  	return h.windowed.Current.RecordValue(v)
    71  }
    72  
    73  // A Histogram collects observed values by keeping bucketed counts. For
    74  // convenience, pb.y two sets of buckets are kept: A cumulative set (i.e.
    75  // data is never evicted) and a windowed set (which keeps only recently
    76  // collected samples).
    77  //
    78  // Top-level methods generally apply to the cumulative buckets; the windowed
    79  // variant is exposed through the Windowed method.
    80  type Histogram struct {
    81  	sync.Mutex
    82  	cumulative *hdrhistogram.Histogram
    83  	sliding    *slidingHistogram
    84  	maxVal     int64
    85  }
    86  
    87  // NewHistogram initializes a given Histogram. The contained windowed histogram
    88  // rotates every 'duration'; both the windowed and the cumulative histogram
    89  // track nonnegative values up to 'maxVal' with 'sigFigs' decimal points of
    90  // precision.
    91  func NewHistogram(duration time.Duration, maxVal int64, sigFigs int) *Histogram {
    92  	dHist := newSlidingHistogram(duration, maxVal, sigFigs)
    93  	h := &Histogram{}
    94  	h.cumulative = hdrhistogram.New(0, maxVal, sigFigs)
    95  	h.sliding = dHist
    96  	h.maxVal = maxVal
    97  	return h
    98  }
    99  
   100  // RecordValue adds the given value to the histogram. Recording a value in
   101  // excess of the configured maximum value for that histogram results in
   102  // recording the maximum value instead.
   103  func (h *Histogram) RecordValue(v int64) {
   104  	h.Lock()
   105  	defer h.Unlock()
   106  
   107  	if h.sliding.RecordValue(v) != nil {
   108  		_ = h.sliding.RecordValue(h.maxVal)
   109  	}
   110  	if h.cumulative.RecordValue(v) != nil {
   111  		_ = h.cumulative.RecordValue(h.maxVal)
   112  	}
   113  }