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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！

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一、核心特性对比：架构设计决定能力边界

日志库	核心优势	典型场景
NLog	XML配置支持异步日志、多目标输出（文件/DB/网络）	企业级复杂日志策略定制
log4net	Apache生态集成、跨语言兼容性强	传统.NET Framework项目维护
Serilog	结构化日志、高性能JSON输出、现代化API设计	微服务架构、ELK日志分析场景

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

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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);}}

日志库/模式	LogCount	平均耗时(ms)	内存分配(MB)	标准差(ms)	特殊现象
Serilog Asynchronous	10,000	2.565	4.69	0.1720	双峰分布警告
NLog Async	10,000	48.338	1.68	3.8510	3个离群值移除
Log4net Sync	10,000	7,486.255	50.65	1,371.2566	无异步支持

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");}}

日志库/模式	Mean (平均耗时)	StdDev (标准差)
Serilog Structured Async	252.8 ns	11.25 ns
NLog Text Async	4,978.7 ns	464.88 ns
Log4net Text Sync	564,903.8 ns	32,919.23 ns

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

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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>

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四、选型决策矩阵

评估维度	权重	Serilog	NLog	log4net
性能	25%	95	85	60
扩展性	20%	90	95	80
易用性	15%	92	85	75
综合得分	100%	90.5	86.5	72.5

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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

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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

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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！