Do you use LoggerMessage in .NET?

Logging is a critical component in modern applications, but it can easily introduce performance overhead.

.NET 6 introduced the LoggerMessageAttribute, a feature in the Microsoft.Extensions.Logging namespace that enables source-generated, highly performant logging APIs. This approach eliminates runtime overheads like boxing and temporary allocations, making it faster than traditional logging methods.

Key performance benefits of LoggerMessageAttribute

• Source Generation: Automatically generates the implementation of partial methods with compile-time diagnostics.
• Improved Performance: Reduces runtime overhead by leveraging compile-time optimizations.
• Flexible Usage: Supports static and instance-based methods with configurable log levels and message templates.

How to use LoggerMessageAttribute

Define logging methods as partial and static to trigger the code generator:

public static partial class Log
{
    [LoggerMessage(
        EventId = 0,
        Level = LogLevel.Critical,
        Message = "Could not open socket to `{HostName}`")]
    public static partial void CouldNotOpenSocket(
        ILogger logger, string hostName);
}

Logging methods can also be used in an instance context by accessing an ILogger field or primary constructor parameter:

public partial class InstanceLoggingExample(ILogger logger)
{
    [LoggerMessage(
        EventId = 0,
        Level = LogLevel.Critical,
        Message = "Could not open socket to `{HostName}`")]
    public partial void CouldNotOpenSocket(string hostName);
}

Using LoggerMessageAttribute with JsonConsole formatter can produce structured logs. In our log messages we can specify custom event names as well as utelize string formatters:

[LoggerMessage(
        EventId = 9,
        Level = LogLevel.Trace,
        EventName = "PropertyValueEvent")]
        Message = "In {City} the average property value is {Value:E}")]
public static partial void PropertyValueInAustralia(ILogger logger, string city double value);

Constraints

When using LoggerMessageAttribute, ensure:

• Logging methods must be partial and return void.
• Logging method names must not start with an underscore.
• Parameter names of logging methods must not start with an underscore.
• Logging methods may not be defined in a nested type.
• Logging methods cannot be generic.
• If a logging method is static, the ILogger instance is required as a parameter.

More information

See this great article on Microsoft Learn which goes into more detail and usage examples: Compile-time logging source generation in .NET.