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From Remko Popma <remko.po...@gmail.com>
Subject Re: defer creation of RollingFileAppender log files when Logger and/or AppenderRef level attribute has a value of "OFF"?
Date Thu, 07 Jul 2016 22:59:58 GMT

Just thinking out loud, Log4j 2 has the ability to start logging to a new log file that is
not explicitly defined in configuration with the RoutingAppender. See https://logging.apache.org/log4j/2.x/faq.html#separate_log_files

You may be able to use this feature, perhaps in combination with a custom Filter. The Filter
would usually DENY all log events, but would start to ACCEPT events for certain products when
these products were selected in some admin gui. 

This solution would require that all log events have the relevant product ID or something
in their context map. Currently the only way to put data in the LogEvent's context map is
via the ThreadContext. (There is a ticket to make this customizable: https://issues.apache.org/jira/browse/LOG4J2-1010).

Can you think about whether these together can form a solution? Maybe experiment a little
with a test program, to see what obstacles come up. 


Sent from my iPhone

> On 2016/07/08, at 4:26, <Cheryl_Mrozienski@Dell.com> <Cheryl_Mrozienski@Dell.com>
> Dell - Internal Use - Confidential
> Hi,
> I am currently using Log4j version 2.3, but might be able to update to a newer version
if that would help.
> I have a log4j2.xml file containing more than thirty RollingFileAppenders (one per product
component).  Most of these RollingFileAppenders will not be written to until the user turns
on logging via our product's user interface.  By default, the AppenderRefs that reference
these RollingFileAppenders have the "level" attribute set to a value of "OFF".  Once the user
turns on logging from the user interface, the "level" attribute will be updated with a value
of "INFO", "DEBUG", etc.  And, once the updated log4j2.xml file is persisted, the code will
then call LoggerContext.reconfigure() to get Log4j to read in the new log4j2.xml file, so
the new log levels take effect.
> My question is whether there is a way to tell Log4j to defer log file creation when nothing
will initially write to the file (e.g. all references to the Appender have a level of "OFF")?
 Having lots of zero sized log files is not that big of an issue, although not completely
optimal.  However, having too many open file handles that are not doing anything, could potentially
become an issue.  Note that I do not have control over the number of Appenders configured
for the product.  Each product component team contributes its Appender and Loggers to log4j2.xml.
> To work around the open file handle issue at server startup time, I am currently using
the Log4j2 private core API calls to loop through the AppenderRefs to determine which ones
are "OFF", and then I'm calling the RollingFileAppender.stop() method to close the output
stream.  If anyone has any ideas that would avoid creating and opening the log files in the
first place, I'd love to hear your thoughts.
> Thanks and regards,
> -Cheryl
> p.s. for reference, the relevant log4j2.xml snippets follow:
> <Appenders>
>    <RollingFile
>      fileName="${sys:com.compellent.msaserviceDir}/etc/compservices/debuglogs/Scheduler/Scheduler.debuglog"
>      filePattern="${sys:com.compellent.msaserviceDir}/etc/compservices/debuglogs/Scheduler/Scheduler_%i.debuglog.gz"
>      name="debug.Scheduler">
>      <PatternLayout>
>        <Pattern>%d{yyyy-MM-dd HH:mm:ss,SSS} %-5p {%C:%M} [%marker] (%t) - %msg%n</Pattern>
>      </PatternLayout>
>      <Policies>
>        <SizeBasedTriggeringPolicy size="50 MB"/>
>      </Policies>
>      <DefaultRolloverStrategy max="10"/>
>      <Filters>
>        <MarkerFilter marker="Scheduler" onMatch="ACCEPT" onMismatch="DENY"/>
>      </Filters>
>    </RollingFile>
> </Appenders>
> <Loggers>
>    <Logger includeLocation="true" level="TRACE" name="debugLogger">
>      <AppenderRef level="DEBUG" ref="debug.ModuleManager"/>
>      <AppenderRef level="OFF" ref="debug.Scheduler"/>
>    </Logger>
> </Loggers>

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