Metrics.Net实践（2）在WEB中应用度量

Gauges

可以画出Http Request执行时间的波形图：
actionInfo表示MVC中的Action，即按照action类型来分组

Metric.Context(this.actionInfo.ActionType)
     .Gauge(counterName, () => milliseconds, Unit.Custom("Milliseconds"));

Counters

记录总的请求数和并发请求数：

public class WebApiApplication : System.Web.HttpApplication
    {
        private readonly Counter totalRequestsCounter = 
               Metric.Context("[Request]").Counter("Total_Requests", Unit.Custom("個"), "request");

        private readonly Counter concurrentRequestsCounter = 
               Metric.Context("[Request]").Counter("Concurrent_Requests", Unit.Custom("個"), "request,concurrent");

        /// <summary>
        /// 應用程序啟動方法
        /// </summary>
        protected void Application_Start()
        {
            GlobalConfiguration.Configure(WebApiConfig.Register);

            Metric.Config
               .WithHttpEndpoint("http://localhost:1234/metrics/");
            //Metric.Config.WithHttpEndpoint("http://+:8898/")//外网可以访问
        }

        /// <summary>
        /// 開始請求
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        protected void Application_BeginRequest(object sender, EventArgs e)
        {
            totalRequestsCounter.Increment();
            concurrentRequestsCounter.Increment();
        }

        /// <summary>
        /// 結束請求
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        protected void Application_EndRequest(object sender, EventArgs e)
        {
            concurrentRequestsCounter.Decrement();
        }
    }

Histograms

度量POST&PUT请求大小的直方图：

public PostAndPutRequestSizeMetric(ActionInfo info)
            : base(info)
        {
            this.histogram = Metric.Context(this.actionInfo.ActionType)
                  .Histogram(COUNTER_NAME, Unit.Bytes, SamplingType.FavourRecent);
        }


        /// <summary>
        /// Constant defining the name of this counter
        /// </summary>
        public const String COUNTER_NAME = "Post & Put Request Size";


        /// <summary>
        /// Reference to the performance counter 
        /// </summary>
        private Histogram histogram;

        public override void OnActionStart()
        {
            var method = this.actionInfo.HttpMethod.ToUpper();
            if (method == "POST" || method == "PUT")
            {
                histogram.Update(this.actionInfo.ContentLength);
            }
        }

Histrogram 的度量值不仅仅是计算最大/小值、平均值，方差，他还展现了分位数（如中位数，或者95th分位数），如75%,90%,98%,99%的数据在哪个范围内。

传统上，中位数（或者其他分位数）是在一个完整的数据集中进行计算的，通过对数据的排序，然后取出中间值（或者离结束1%的那个数字，来计算99th分位数）。这种做法是在小数据集，或者是批量计算的系统中，但是在一个高吞吐、低延时的系统中是不合适的。

一个解决方案就是从数据中进行抽样，保存一个少量、易管理的数据集，并且能够反应总体数据流的统计信息。使我们能够简单快速的计算给定分位数的近似值。这种技术称作reservoir sampling。

Meters

Meter度量一系列事件发生的比率：

 public DeltaExceptionsThrownMetric(ActionInfo info)
            : base(info)
        {
            this.deltaExceptionsThrownCounter
                = Metric.Context(this.actionInfo.ActionType).Meter(COUNTER_NAME, Unit.Errors, TimeUnit.Seconds);
        }

        /// <summary>
        /// Constant defining the name of this counter
        /// </summary>
        public const String COUNTER_NAME = "Errors";


        /// <summary>
        /// Reference to the performance counter 
        /// </summary>
        private Meter deltaExceptionsThrownCounter;


        /// <summary>
        /// Method called by the custom action filter after the action completes
        /// </summary>
        /// <remarks>
        /// If exceptionThrown is true, then the Total Exceptions Thrown counter will be 
        /// incremented by 1
        /// </remarks>
        public override void OnActionComplete(long elapsedTicks, bool exceptionThrown)
        {
            if (exceptionThrown)
                this.deltaExceptionsThrownCounter.Mark();
        }

Meter需要除了Name之外的两个额外的信息，事件类型（enent type）跟比率单位（rate unit）。事件类型简单的描述Meter需要度量的事件类型，在上面的例子中，Meter是度量失败的请求数，所以他的事件类型也叫做“Errors”。比率单位是命名这个比率的单位时间，在上面的例子中，这个Meter是度量每秒钟的失败请求次数，所以他的单位就是秒。这两个参数加起来就是表述这个Meter，描述每秒钟的失败请求数。

Timers

Timer是Histogram跟Meter的一个组合

public TimerForEachRequestMetric(ActionInfo info)
            : base(info)
        {
            String controllerName = this.actionInfo.ControllerName;
            String actionName = this.actionInfo.ActionName;
            string counterName = string.Format("{0}{1}", controllerName, actionName);

            this.averageTimeCounter = Metric.Context(this.actionInfo.ActionType)
                 .Timer(counterName, Unit.Requests, SamplingType.FavourRecent,
                TimeUnit.Seconds, TimeUnit.Milliseconds);
        }

        #region Member Variables
        private Timer averageTimeCounter;
        #endregion

        /// <summary>
        /// Method called by the custom action filter after the action completes
        /// </summary>
        /// <remarks>
        /// This method increments the Average Time per Call counter by the number of ticks
        /// the action took to complete and the base counter is incremented by 1 (this is
        /// done in the PerfCounterUtil.IncrementTimer() method).  
        /// </remarks>
        /// <param name="elapsedTicks">A long of the number of ticks it took to complete the action</param>
        public override void OnActionComplete(long elapsedTicks, bool exceptionThrown)
        {
            averageTimeCounter.Record(elapsedTicks, TimeUnit.Nanoseconds);
        }

REF :http://www.cnblogs.com/mrblue/p/7080242.html