dl/lib/logger/metrics/HistogramMetric.js

DreamLab Libs

var core = require('core');

var HdrHistogram = require('native-hdr-histogram');
var Types = core.common.Types;

var GaugeMetric = require('./GaugeMetric.js').GaugeMetric;

var HistogramMetric = function (name, buckets) {
    GaugeMetric.call(this, name);

    if (!Types.isArray(buckets)) {
        throw new Error('Buckets need to be an array');
    }

    if (buckets.length < 2) {
        throw new Error('Buckets need to have at least two elements');
    }

    this._buckets = buckets.sort(function (a, b) { return a - b; });
    this._values = Array.apply(null, Array(this._buckets.length + 1)).map(function () { return 0; });

    var min = this._buckets[0] >= 1 ? this._buckets[0] : 1;
    var max = this._buckets[this._buckets.length - 1];

    this._histogram = new HdrHistogram(min, max);
};

HistogramMetric.prototype = Object.create(GaugeMetric.prototype);

HistogramMetric.prototype.update = function (value) {
    this._histogram.record(value);

    var idx = 0;

    // [ 1, 3 ]
    // -1 -> 0
    //  1 -> 1
    //  2 -> 1
    //  3 -> 2
    //  4 -> 2

    while (idx < this._buckets.length && value >= this._buckets[idx]) {
        idx++;
    }

    this._values[idx]++;

    return GaugeMetric.prototype.update.call(this, value);
};

HistogramMetric.prototype.dump = function () {
    var data = {
        'p50': this._histogram.percentile(50),
        'p95': this._histogram.percentile(95),
        'p99': this._histogram.percentile(99),
        'stddev': this._histogram.stddev()
    };

    var keys = Object.keys(data);
    var that = this;

    keys = keys.map(function (key) {
        return {
            'key': that._name + '.' + key,
            'value': that._dumpValue(1, data[key])
        };
    });

    if (this._values[0] > 0) {
        keys.push({
            'key': this._name + '.min_to_' + this._buckets[0],
            'value': {
                'count': this._values[0]
            }
        });
    }

    for (var i = 1, l = this._buckets.length; i < l; i++) {
        if (this._values[i] > 0) {
            keys.push({
                'key': this._name + '.' + this._buckets[i - 1] + '_to_' + this._buckets[i],
                'value': {
                    'count': this._values[i]
                }
            });
        }
    }

    if (this._values[this._buckets.length] > 0) {
        keys.push({
            'key': this._name + '.' + this._buckets[this._buckets.length - 1] + '_to_max',
            'value': {
                'count': this._values[this._buckets.length]
            }
        })
    }

    keys = keys.concat(GaugeMetric.prototype.dump.call(this));

    return keys;
};

exports.HistogramMetric = HistogramMetric;