Correct way of using log4net (logger naming)

Question

There are two ways of configuring and using log4net. First one is when I can configure my own appender and associated logger:

<!-- language: xml -->

<appender name="myLogAppender" type="log4net.Appender.RollingFileAppender" >
    <file value="Logs\myLog.log" />
    <layout type="log4net.Layout.PatternLayout">
        <conversionPattern value="%date %level - %message%n" />
    </layout>
</appender>

<logger name="myLog">
    <level value="All"></level>
    <appender-ref ref="myLogAppender" />
</logger>

And then when I want to write something in log, I can do the following:

ILog log = LogManager.GetLogger("myLog");
log.Info("message");

Another way to use it is to configure root to be as detailed as I want:

<!-- language: xml -->

<root>
    <level value="Error" />
    <appender-ref ref="myLogAppender" />
</root>

And in this case I can log messages like this:

ILog log = LogManager.GetLogger(typeof(Bar));
log.Info("message");

The benefits of second approach is that you can enable or disable some messages on the fly. But the problem is that I'm developing in EPiServer CMS and it has its own logging system that uses log4net and if I enable info logging at root level, then a lot of system logs will be written.

How do you use log4net? Each part of a system writes in its own logger, or everything is written in default logger, and configuration decides what to do next?

Answer 1

Regarding how you log messages within code, I would opt for the second approach:

ILog log = LogManager.GetLogger(typeof(Bar));
log.Info("message");

Where messages sent to the log above will be 'named' using the fully-qualifed type Bar, e.g.

MyNamespace.Foo.Bar [INFO] message

The advantage of this approach is that it is the de-facto standard for organising logging, it also allows you to filter your log messages by namespace. For example, you can specify that you want to log INFO level message, but raise the logging level for Bar specifically to DEBUG:

<log4net>
    <!-- appenders go here -->
    <root>
        <level value="INFO" />
        <appender-ref ref="myLogAppender" />
    </root>

    <logger name="MyNamespace.Foo.Bar">
        <level value="DEBUG" />
    </logger>
</log4net>

The ability to filter your logging via name is a powerful feature of log4net, if you simply log all your messages to "myLog", you loose much of this power!

Regarding the EPiServer CMS, you should be able to use the above approach to specify a different logging level for the CMS and your own code.

For further reading, here is a codeproject article I wrote on logging:

• The Art Of Logging