Npgsql中Activity.Duration远低于实际耗时的原因是什么？

我搞不懂Npgsql是怎么计算Duration的，用Stopwatch捕获的耗时比它高一个数量级，原本以为这两个测量结果应该接近得多。

在我的机器上得到如下时间：

Activity.Duration:   00:00:00.0174913
Stopwatch duration:  00:00:00.1394318

复现步骤 #

1. 创建.NET控制台应用代码 #

using System.Diagnostics;
using Npgsql;
using OpenTelemetry;
using OpenTelemetry.Resources;
using OpenTelemetry.Trace;

using var tracerProvider = Sdk.CreateTracerProviderBuilder()
    .SetResourceBuilder(ResourceBuilder.CreateDefault().AddService("npgsql-tester"))
    .SetSampler(new AlwaysOnSampler())
    .AddSource("MyApp")
    .AddNpgsql()
    .AddConsoleExporter()
    .Build();

var connectionString = "Host=localhost;Database=db;Username=dbuser;Password=dbpassword;";
await using var dataSource = NpgsqlDataSource.Create(connectionString);
await using var cmd = dataSource.CreateCommand("SELECT 1");

var timer = new Stopwatch();
timer.Start();

await cmd.ExecuteScalarAsync();

timer.Stop();
Console.WriteLine($"Stopwatch duration: {timer.Elapsed}");

2. 添加依赖包 #

dotnet add package Npgsql -v 7.0.2
dotnet add package Npgsql.OpenTelemetry -v 7.0.2
dotnet add package OpenTelemetry.Exporter.Console -v 1.4.0
dotnet add package OpenTelemetry.Instrumentation.SqlClient -v 1.0.0-rc9.13

3. 启动本地Postgres实例（Docker） #

docker run --name npgsql-duration -p 5432:5432 -e POSTGRES_DB=db -e POSTGRES_USER=dbuser -e POSTGRES_PASSWORD=dbpassword -d postgres

内容的提问来源于stack exchange，提问作者Couper