I have a log4cpp implementation in a multiple process environment . Logger is configured once during initialization and then is shared among forked processes which server http requests.
During first minute or so , I see the logs rolls perfectly fine at the query per second load( say it runs at 100qps). After that, the log slows down dramatically. So, I logged pid as well and notice that only one process gets to write to the log for a time duration ( around 10-15 seconds) and then another process starts writing and so on so forth . Processes don't die. They just don't get a chance to write.
This is different from what happens when the server starts . At that time, every other log line is written by a different process. ( Also, I write one-log-line per process at the end of serving the request. )
At this point, I can't think of what could be going wrong. This is how my log4cpp conf file looks
log4cpp.rootCategory=DEBUG,rootAppender
log4cpp.appender.rootAppender=org.apache.log4cpp.RollingFileAppender
log4cpp.appender.rootAppender.fileName=/tmp/mylogfile.log
log4cpp.appender.rootAppender.layout=org.apache.log4cpp.PatternLayout
log4cpp.appender.rootAppender.layout.ConversionPattern=%d|%p|%m%n
log4cpp.category.http.server.main=INFO,MAIN
log4cpp.additivity.http.server.main=false
log4cpp.appender.MAIN=org.apache.log4cpp.RollingFileAppender
log4cpp.appender.MAIN.maxBackupIndex=10
log4cpp.appender.MAIN.maxFileAge=1
log4cpp.appender.MAIN.append=true
log4cpp.appender.MAIN.fileName=/tmp/mylogfile.log
log4cpp.appender.MAIN.layout=org.apache.log4cpp.PatternLayout
log4cpp.appender.MAIN.layout.ConversionPattern=%d|%p|%m%n
Edit: more updates : Thanks @Botje for your time.
I see that whenever a new child process is created , it is only that process that gets to write to the log. That tells me that all the reference other processes were holding become invalid.
I also tried setting additive property to true. With that , server starts properly writing into the /tmp/myfile.log and then switches to writing into /tmp/myfile.log.1 withing a minute . And then stops writing after a minute. At that point logs gets directed to stderr which is directed to another log file.
Also,
I did notice that the log4cpp FileAppender uses seek to determine the file size before writing log entries. If the file handle is shared between processes that will cause writes to end up at the start of the file instead of the end. Even if you fix that, you still have multiple processes that think they are in charge of log file rotation.
I suggest you have all processes write to a common udp/tcp/Unix socket and designate one process that collects all log entries and actually writes it to a file. You don't have to reinvent the wheel, you can use the syslog protocol and either the system syslog or a copy running in userspace.