log4net configuration: Add an appender of type, log4net.Appender.TraceAppender to the web.config,
<appender name="DebugSQL" type="log4net.Appender.TraceAppender">
<layout type="log4net.Layout.PatternLayout">
<conversionPattern value="%date [%thread] %-5level %logger [%property{NDC}] - %message%newline" />
</layout>
</appender>
NHibernate logs all SQL statements using a logger named, NHibernate.SQL.
Add a logger to the web.config. The name must be NHibernate.SQL, and DEBUG must be assigned to the level for this to work:
<logger name="NHibernate.SQL" additivity="false">
<level value="DEBUG"/>
<appender-ref ref="NHibernate.SQL" />
</logger>
<logger name="NHibernate.SQL" additivity="false">
<level value="DEBUG"/>
<appender-ref ref="NHibernate.SQL" />
</logger>