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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！
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
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：
- Serilog异步批处理机制在并发场景下表现出色
- log4net同步锁导致严重线程竞争
- 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
| 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 |
五、终极选型建议
-
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
-
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
-
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
- 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>
- 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; }
- 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！