A change made for
LOG4NET-205 has the LoggingEvent.CreateCompositeProperties method get the UserName property for every log event. Since getting the UserName is very slow, this change has a significant impact on performance in log4net.
In one trace captured with dotTrace on a large web application we found that the get UserName property (called from CreateCompositeProperties) accounted for 34% of all time spent in log4net code.
Our workaround for the issue has been to "fix" the UserName property by adding <fix value="32" /> to all our appenders.