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Namespace metric

Table of Contents

Introduction

Similar as logging, metric is a basic requirement for creating monitorable services. Metric API enables developers to use their own metric system in both JavaScript and C++ (addon) world.

A metric has its identity containing following information:

  • Section: The group or category of the metric.
  • Name: Name of the metric. Section/Name combination should be unique in the system.
  • Type: Type of the metric, which can be
    • Number: An absolute number, e.g: PrivateBytes.
    • Rate: A flowing volume in number, e.g: QueryPerSecond.
    • Percentile: An absolute number that needs to be sampled by percentiles, e.g: SuccessLatency.
  • Dimensions: A metric can have multiple dimensions, each dimension can bind with a string value at runtime. e.g: IncomingRequestRate can have 2 dimensions: ['client-id', 'request-type'].

Metrics are process-wise objects, which can be used across zones.

C++ API

Interface Metric

 /// <summary> Enumeration of metric type. </summary>
    enum class MetricType {
        Number = 0,
        Rate,
        Percentile,
    };

    /// <summary> Interface to represent a multi-dimensional metric with a maximum dimensionality of 64. </summary>
    class Metric {
    public:

        /// <summary> Sets a metric value with variadic dimension arguments. </summary>
        /// <param name="value"> Int64 value. </param>
        /// <param name="numberOfDimensions"> Number of dimensions being set. </param>
        /// <param name="dimensionValues"> Array of dimension value names. </param>
        /// <returns> Success/Fail. </returns>
        /// <remarks>
        ///     The number of dimension values must exactly match the number of dimensions provided when
        ///     creating this metric.
        /// </remarks>
        virtual bool Set(int64_t value, size_t numberOfDimensions, const char* dimensionValues[]) = 0;

        /// <summary>
        ///     Increments a metric value with variadic dimension arguments.
        ///     Use mainly to simplify rate counters.
        /// </summary>
        /// <param name="value"> UInt64 value to increment. </param>
        /// <param name="numberOfDimensions"> Number of dimensions being set. </param>
        /// <param name="dimensionValues"> Array of dimension value names. </param>
        /// <returns> Success/Fail. </returns>
        /// <remarks>
        ///     The number of dimension values must exactly match the number of dimensions
        ///     provided when creating this metric.
        /// </remarks>
        virtual bool Increment(uint64_t value, size_t numberOfDimensions, const char* dimensionValues[]) = 0;

        /// <summary>
        ///     Decrements metric value with variadic dimension arguments.
        ///     Use mainly to simplify rate counters.
        /// </summary>
        /// <param name="value"> UInt64 value to decrement. </param>
        /// <param name="numberOfDimensions"> Number of dimensions being set. </param>
        /// <param name="dimensionValues"> Array of dimension value names. </param>
        /// <returns> Success/Fail. </returns>
        /// <remarks>
        ///     The number of dimension values must exactly match the number of dimensions
        ///     provided when creating this metric.
        /// </remarks>
        virtual bool Decrement(uint64_t value, size_t numberOfDimensions, const char* dimensionValues[]) = 0;

        /// <summary> Explicitly destroys the Metric. </summary>
        /// <remarks>
        ///     Consumers are not required to call this.
        ///     The MetricProvider owns this class and will automatically perform cleanup on shutdown.
        /// </remarks>
        virtual void Destroy() = 0;

    protected:

        ///<summary> Prevent calling delete on the interface. Must use Destroy! </summary>
        virtual ~Metric() = default;
    };

Interface MetricProvider

    /// <summary> Interface for a generic metric provider. </summary>
    /// <remarks> 
    ///     Ownership of this metric provider belongs to the shared library which created it. Hence the explicit
    ///     Destroy method in this class. To simplify memory management across multiple shared libraries, this class
    ///     can only be created via a factory method provided by the shared library. When it is no longer needed,
    ///     the caller may call Destroy() which will tell the shared library which created it to dispose of the object.
    /// </remarks>
    class MetricProvider {
    public:

        /// <summary>
        ///     Gets or creates a N-dimensional metric. Metric objects are owned and cached by this class.
        ///     Up to 64 dimensions may be used.</summary>
        /// <param name="section"> Section of the metric.</param>
        /// <param name="name"> Name of the metric.</param>
        /// <param name="type"> Type of the metric.</param>
        /// <param name="dimensions">
        ///     Number of dimensions requested for this metric.
        ///     Represents the size of the array passed in for p_dimensionNames.
        /// </param>
        /// <param name="dimensionNames"> Array of dimension names being requested for this metric.</param>
        /// <remarks>
        ///     The IMetric class returned is owned and cached by this class.
        ///     Callers are not required to call destroy() on the Metric.
        /// </remarks>
        virtual Metric* GetMetric(
            const char* section,
            const char* name,
            MetricType type,
            size_t dimensions,
            const char* dimensionNames[]) = 0;

        ///<summary> Explicitly destroys the metric provider. </summary>
        virtual void Destroy() = 0;

    protected:

        ///<summary> Prevent calling delete on the interface. Must use Destroy! </summary>
        virtual ~MetricProvider() = default;
    };

function MetricProvider& GetMetricProvider()

/// <summary> Exports a getter function for retrieves the configured metric provider. </summary>
NAPA_API MetricProvider& GetMetricProvider();

JavaScript API

enum MetricType

export enum MetricType {
    Number = 0,
    Rate,
    Percentile,
}

Class Metric

Class to manipulate metrics in JavaScript.

set(value: number, dimensions?: string[]): void

Set absolute value on an instance of the metric constrained by dimension values. Example:

// Create a percentile metric to measure end-to-end latency, with 1 dimension of client-id.
latency = napa.metric.get(
    'app1',
    'end-to-end-latency',
    napa.metric.MetricType.Percentile, 
    ['client-id']);

// Set end-to-end latency of current request to 100, with client-id 'client1'.
latency.set(100, ['client1']);

increment(dimensions?: string[]): void

Increment the value of an instance of the metric constrained by dimension values.

Example:

// Create a percentile metric to measure end-to-end latency, with 1 dimension of client-id.
latency = napa.metric.get(
    'app1',
    'qps',
    napa.metric.MetricType.Rate, 
    ['client-id']);

// Increment QPS of client-id 'client1'.
latency.increment(['client1']);

decrement(dimensions?: string[]): void

Decrement the value of an instance of the metric constrained by dimension values.

function get(section: string, name: string, type: MetricType, dimensions: string[] = []): Metric

Create a metric with an identity consisting of section, name, type and dimensions. If a metric already exists with given parameters, returns existing one.

Example:

import * as napa from 'napajs';
let metric = napa.metric.get(
    'app1', 
    'counter1', 
    napa.metric.MetricType.Number, 
    []);
metric.increment([]);

Using custom metric providers

Developers can hook up custom metric provider by calling the following before creation of any zones:

napa.runtime.setPlatformSettings({
    "metricProvider": "<custom-metric-provider-module-name>"
}

Developing custom metric providers

TBD