C#主流日志库深度对比：NLog、log4net与Serilog如何选择？

日志作为系统的"黑匣子"，是故障排查与性能分析的基石。但在.NET生态中，NLog、log4net、Serilog三大主流日志库常让开发者陷入选择困难。本文通过多维实测，带你穿透技术迷雾！

一、核心特性对比：架构设计决定能力边界

架构差异解析：

• Serilog采用结构化日志模型，直接生成JSON格式日志，省去文本解析开销
• NLog通过异步队列实现高吞吐，支持200+输出目标扩展
• log4net采用同步写入模型，在并发场景下易成性能瓶颈

二、性能实测：吞吐量相差2918倍的秘密

1. 基准测试（单线程1万条日志）

代码实现：

    using BenchmarkDotNet.Attributes;
    using log4net;
    using log4net.Appender;
    using log4net.Config;
    using log4net.Core;
    using log4net.Filter;
    using log4net.Layout;
    using NLog;
    using Serilog;

    [MemoryDiagnoser]
    [ThreadingDiagnoser]
    public class LogBenchmarks
    {
        private static readonly Serilog.ILogger serilogLogger = Log.Logger;
        private static readonly Logger nlogLogger = NLog.LogManager.GetCurrentClassLogger();
        private static readonly ILog log4netLogger = log4net.LogManager.GetLogger(typeof(LogBenchmarks));

        [Params(10000)]
        public int LogCount { get; set; }

        [GlobalSetup]
        public void Setup()
        {
            // Serilog配置（异步文件写入）
            Log.Logger = new LoggerConfiguration()
                .WriteTo.Async(a => a.File("serilog.log"), bufferSize: 1000)
                .CreateLogger();

            // NLog配置（异步文件写入）
            var nlogConfig = new NLog.Config.LoggingConfiguration();
            var asyncFileTarget = new NLog.Targets.FileTarget("asyncFile")
            { 
                FileName = "nlog.log",
                BufferSize = 1000,
            };
            nlogConfig.AddRuleForAllLevels(asyncFileTarget);
            NLog.LogManager.Configuration = nlogConfig;

            // log4net配置（同步文件写入）
            var logRepository = log4net.LogManager.GetRepository(System.Reflection.Assembly.GetEntryAssembly());
            RollingFileAppender appender = new RollingFileAppender
            {
                Name = "root",
                File = "log\\log_",
                AppendToFile = true,
                LockingModel = new FileAppender.MinimalLock(),
                RollingStyle = RollingFileAppender.RollingMode.Date,
                DatePattern = "yyyyMMdd-HH\".log\"",
                StaticLogFileName = false,
                MaxSizeRollBackups = 10,
                Layout = new PatternLayout("[%d{HH:mm:ss.fff}] %-5p %c T%t:%n%m%n")
            };
            appender.ClearFilters();
            appender.AddFilter(new LevelMatchFilter() { LevelToMatch = Level.Debug });
            BasicConfigurator.Configure(logRepository, appender);
            appender.ActivateOptions();
        }

        [Benchmark(Description = "Serilog Async")]
        public void SerilogTest()
        {
            for (int i = 0; i < LogCount; i++)
                serilogLogger.Information("Log entry {Number}", i);
        }

        [Benchmark(Description = "NLog Async")]
        public void NLogTest()
        {
            for (int i = 0; i < LogCount; i++)
                nlogLogger.Info("Log entry {0}", i);
        }

        [Benchmark(Description = "log4net Sync")]
        public void Log4NetTest()
        {
            for (int i = 0; i < LogCount; i++)
                log4netLogger.InfoFormat("Log entry {0}", i);
        }
    }

2. 并发测试（100线程写入）

    [MemoryDiagnoser]
    [ThreadingDiagnoser]
    public class StructBenchmark
    {
        private static readonly Serilog.ILogger serilogLogger = Log.Logger;
        private static readonly NLog.Logger nlogLogger = NLog.LogManager.GetCurrentClassLogger();
        private static readonly ILog log4netLogger = log4net.LogManager.GetLogger(typeof(LogBenchmarks));

        [GlobalSetup]
        public void Setup()
        {
            // Serilog配置（异步文件写入）
            Log.Logger = new LoggerConfiguration()
                .WriteTo.File("serilog.log")
                .CreateLogger();

            // NLog配置（异步文件写入）
            var nlogConfig = new NLog.Config.LoggingConfiguration();
            var asyncFileTarget = new NLog.Targets.FileTarget("syncFile ")
            {
                FileName = "nlog.log",
                BufferSize = 1000,
            };
            nlogConfig.AddRuleForAllLevels(asyncFileTarget);
            NLog.LogManager.Configuration = nlogConfig;

            // log4net配置（同步文件写入）
            var logRepository = log4net.LogManager.GetRepository(System.Reflection.Assembly.GetEntryAssembly());
            RollingFileAppender appender = new RollingFileAppender
            {
                Name = "root",
                File = "log\\log_",
                AppendToFile = true,
                LockingModel = new FileAppender.MinimalLock(),
                RollingStyle = RollingFileAppender.RollingMode.Date,
                DatePattern = "yyyyMMdd-HH\".log\"",
                StaticLogFileName = false,
                MaxSizeRollBackups = 10,
                Layout = new PatternLayout("[%d{HH:mm:ss.fff}] %-5p %c T%t:%n%m%n")
            };
            appender.ClearFilters();
            appender.AddFilter(new LevelMatchFilter() { LevelToMatch = Level.Debug });
            BasicConfigurator.Configure(logRepository, appender);
            appender.ActivateOptions();
        }

        [Benchmark(Description = "Serilog Structured Sync")]
        public void SerilogStructured()
        {
            var user = new { Name = "Alice", Age = 30 };
            serilogLogger.Information("User {Name} logged in", user.Name);
        }

        [Benchmark(Description = "NLog Text Sync")]
        public void NLogText()
        {
            var user = new { Name = "Alice", Age = 30 };
            nlogLogger.Info($"User {user.Name} logged in");
        }
        [Benchmark(Description = "log4net Text Sync")]
        public void Log4NetText()
        {
            var user = new { Name = "Alice", Age = 30 };
            log4netLogger.InfoFormat($"User {user.Name} logged in");
        }
    }

关键结论：

1. Serilog异步批处理机制在并发场景下表现出色
2. log4net同步锁导致严重线程竞争
3. NLog在吞吐量与稳定性间取得平衡

三、实战代码示例

1. Serilog结构化日志实现

// 配置支持JSON输出的日志
Log.Logger = new LoggerConfiguration()
    .WriteTo.Console(new JsonFormatter())
    .WriteTo.Elasticsearch(new ElasticsearchSinkOptions(new Uri("http://es:9200")))
    .CreateLogger();

// 结构化日志记录
var user = new { Id = 1, Name = "张三" };
Log.Information("用户登录 {@User}，登录IP {IP}", user, "192.168.1.1");

输出效果：

{
  "Timestamp": "2023-12-20T14:30:22.123Z",
  "Level": "Information",
  "Message": "用户登录 { Id: 1, Name: 张三 }, 登录IP 192.168.1.1",
  "User": { "Id": 1, "Name": "张三" },
  "IP": "192.168.1.1"
}

2. NLog多目标配置

<!-- NLog.config -->
<targets>
    <target name="file" xsi:type="File" 
            fileName="${basedir}/logs/${shortdate}.log"
            layout="${longdate}|${level}|${message}"/>
    
    <target name="db" xsi:type="Database"
            commandText="INSERT INTO Logs(Date,Level,Message) VALUES(@date,@level,@message)">
        <parameter name="@date" layout="${date}"/>
        <parameter name="@level" layout="${level}"/>
        <parameter name="@message" layout="${message}"/>
    </target>
</targets>

<rules>
    <logger name="*" minlevel="Info" writeTo="file,db"/>
</rules>

四、选型决策矩阵

五、终极选型建议

1. 微服务/云原生场景

   • 首选Serilog：结构化日志与ELK生态无缝对接
   • 典型组合：Serilog + Elasticsearch + Grafana

2. 传统企业级系统

   • 选择NLog：通过XML配置实现复杂日志路由策略
   • 推荐方案：NLog异步模式 + 数据库存储

3. 遗留系统维护

   • 谨慎使用log4net：建议逐步替换或启用异步包装器
   • 过渡方案：log4net.Async扩展包 + 性能监控

避坑指南：

• 避免在log4net中直接使用同步日志核心组件
• Serilog需注意对象序列化深度控制
• NLog配置文件需启用async="true"属性

六、性能优化技巧

1. 异步日志全攻略

// Serilog异步配置
.WriteTo.Async(a => a.File("logs/app.log"), 
    blockWhenFull: true,  // 队列满时阻塞
    bufferSize: 10000)     // 缓冲区大小

// NLog异步配置
<target name="asyncFile" xsi:type="AsyncWrapper" 
    queueLimit="5000" 
    overflowAction="Block">
    <target xsi:type="File" fileName="logs/nlog.log"/>
</target>

2. 结构化日志优化原则

• 避免记录大型对象（超过1MB）
• 敏感字段使用Destructurama.Attribute标记

[NotLogged] 
public string Password { get; set; }

3. 高性能日志实践

• 禁用不必要的日志级别（生产环境关闭Debug）
• 采用批处理写入（如Serilog的PeriodicBatching）
• 文件日志启用滚动归档策略

结语

通过本文的深度对比可见，Serilog凭借现代化的设计理念在性能与功能上全面领先，而NLog在传统企业级场景仍具优势。建议新项目优先选择Serilog，老系统逐步迁移替换log4net。你的项目用哪个日志库？欢迎评论区交流实战经验！