I might have figured out the issue:
https://issues.apache.org/jira/browse/LOG4NET-291

Regards,
Chun Kit

p.s. Just joined the mailing list. Thought that replies will be sent
to a special email address (so that it'll be put in the same thread),
and I didn't (know how to) update the original thread without a reply
email. From this email it seems it's threaded simply based on email
subject and content. I shouldn't have thought too much. :)

On Sun, Apr 10, 2011 at 2:14 PM, Ron Grabowski <rongrabowski@yahoo.com> wrote:
> When I change your code to:
> for (int i1 = 0; i1 <= 20; i1++)
> {
>     for (int i2 = 0; i2 < 1000; i2++)
>     {
>         log.Debug("" + i2 + " " + superLongText);
>     }
> }
> the 3 files are created.
> The small file size after 20 runs is probably caused because one of the
> files is 10mb and the other file has been reset. I'm not sure why that
> occurs but it seems like the RFA maintains some sort of internal roll over
> state that isn't preserved when the program starts up again.
>
> ________________________________
> From: Lee Chun Kit <chunkit85@gmail.com>
> To: log4net-user@logging.apache.org
> Sent: Monday, April 4, 2011 5:54 AM
> Subject: RollingFileAppender does not seem to preserve old log messages
>
> Here is the configuration xml I am using:
> <log4net debug="true">
>     <appender name="RollingLogFileAppender"
> type="log4net.Appender.RollingFileAppender">
>         <lockingModel type="log4net.Appender.FileAppender+ExclusiveLock" />
>         <file value="./output/" />
>         <appendToFile value="true" />
>         <rollingStyle value="Composite" />
>         <datePattern value="'LoggerTest'yyyyMMdd'.log'" />
>         <maxSizeRollBackups value="-1" />
>         <maximumFileSize value="10MB" />
>         <staticLogFileName value="false" />
>         <layout type="log4net.Layout.PatternLayout">
>             <conversionPattern value="%date [%level] %message%newline" />
>         </layout>
>     </appender>
>     <logger name="Logger" additivity="false">
>         <level value="DEBUG" />
>         <appender-ref ref="RollingLogFileAppender" />
>     </logger>
> </log4net>
> ---
> Here are the significant portions of my code:
>
>     static readonly string superLongText = new string('a', 1024);
>     static readonly log4net.ILog log =
> log4net.LogManager.GetLogger("Logger");
>
>     static void Main(string[] args)
>     {
>         log4net.Config.XmlConfigurator.Configure("./TestConfig.xml")));
>
>         for (int i = 0; i < 1000; i++)
>         {
>             log.Debug("" + i + " " + superLongText);
>         }
>     }
> ---
> Total size (in bytes) of the generated logs after each execution of my
> program:
> 01: 1061890
> 02: 2123780
> 03: 3185670
> 04: 4247560
> 05: 5309450
> 06: 6371340
> 07: 7433230
> 08: 8495120
> 09: 9557010
> 10: 10618900
> 11: 11680790
> 12: 12742680
> 13: 13804570
> 14: 14866460
> 15: 15928350
> 16: 16990240
> 17: 18052130
> 18: 19114020
> 19: 20175910
> 20: 10751650
> ---
> log files:
>   LoggerTest20110404.log
>   LoggerTest20110404.log.1
> ---
> After run 19, LoggerTest20110404.log is 9463KB (almost 10MB), and
> LoggerTest20110404.log.1 is 10241KB.
> After run 20, LoggerTest20110404.log is 260KB, and
> LoggerTest20110404.log.1 is 10241KB. However, file
> LoggerTest20110404.log.2 is not created (I expect the logger to do
> so).
>
> Does anyone know why is it the case that the log information is not
> preserved between run 19 and run 20? May I know if it is an error in
> my xml configuration or a limitation of the RollingFileAppender and
> the combination of settings I used?
>
> Thanks.
>
> Regards,
> Chun Kit
>
>
>