How can I vary the behavior of an appender by logger

Question

I have an appender that calls a stored procedure to to write a log record. It looks like this (trimmed for brevity):

<log4net>
  <root>
    <level value="WARN" />
    <appender-ref ref="ElsAppender" />
  </root>
  <appender name="LogAppender" type="LoggerAssembly.Appender, LoggerAssembly">
    <bufferSize value="1" />
    <reconnectonerror value="True" />
    <parameter>
      <parameterName value="@EntryDate" />
      <dbType value="DateTime" />
      <layout type="log4net.Layout.RawTimeStampLayout" />
    </parameter>
    <parameter>
      <parameterName value="@message" />
      <dbType value="String" />
      <size value="40000" />
      <layout type="log4net.Layout.PatternLayout">
        <conversionPattern value="%message" />
      </layout>
    </parameter>
  </appender>
</log4net>

Note the size field of the message parameter is set to 40,000.

I have a logger however where I need the message length to be much longer. How do I change this setting for that specific logger. I tried cloning the LogAppender and changing the size value, like this:

<log4net>
  <root>
    <level value="WARN" />
    <appender-ref ref="LogAppender" />
  </root>
  <logger name="SpecialLogger">
    <level value="INFO" />
    <appender-ref ref="SpecialLogAppender" />
  </logger>
  <appender name="LogAppender" type="LoggerAssembly.Appender, LoggerAssembly">
    <bufferSize value="1" />
    <reconnectonerror value="True" />
    <parameter>
      <parameterName value="@EntryDate" />
      <dbType value="DateTime" />
      <layout type="log4net.Layout.RawTimeStampLayout" />
    </parameter>
    <parameter>
      <parameterName value="@message" />
      <dbType value="String" />
      <size value="40000" />
      <layout type="log4net.Layout.PatternLayout">
        <conversionPattern value="%message" />
      </layout>
    </parameter>
  </appender>
  <appender name="SpecialLogAppender" type="LoggerAssembly.Appender, LoggerAssembly">
    <bufferSize value="1" />
    <reconnectonerror value="True" />
    <parameter>
      <parameterName value="@EntryDate" />
      <dbType value="DateTime" />
      <layout type="log4net.Layout.RawTimeStampLayout" />
    </parameter>
    <parameter>
      <parameterName value="@message" />
      <dbType value="String" />
      <size value="400000" />
      <layout type="log4net.Layout.PatternLayout">
        <conversionPattern value="%message" />
      </layout>
    </parameter>
  </appender>
</log4net>

but that results in the message from the SpecialLogger being logged twice, once by the LogAppender and once by the SpecialLogAppender. Any ideas?

Answer 1

You need to add additivity="false" to your special logger definition:

<logger name="SpecialLogger" additivity="false">
  <level value="INFO" />
  <appender-ref ref="SpecialLogAppender" />
</logger>

Answer 2

You need to add a suitable <filter> element to your log4net appender(s). See

• http://logging.apache.org/log4net/release/manual/configuration.html#filters
• http://logging.apache.org/log4net/release/sdk/log4net.Filter.html
• http://logging.apache.org/log4net/release/sdk/index.html

Log4net appenders are checked in document order, so your special appender needs to precede the default appender. Then something like this ought to do yo:

<appender name="SpecialAppender" type="log4net.Appender.FileAppender">
  <file value="log.txt" />
  <filter type="log4net.Filter.LoggerMatchFilter">
    <loggerToMatch value="your-logger-name-here">
    <acceptOnMatch="true"
  </filter>
  <layout type="log4net.Layout.SimpleLayout" />
</appender>
<appender name="DefaultAppender" type="log4net.Appender.FileAppender">
  <file value="log.txt" />
  <filter type="log4net.Filter.LoggerMatchFilter">
    <loggerToMatch value="your-logger-name-here">
    <acceptOnMatch="false"
  </filter>
  <layout type="log4net.Layout.SimpleLayout" />
</appender>