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From "Ralph Goers (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (LOG4J2-1784) Large values for max in DefaultRolloverStrategy blocks application
Date Sun, 15 Jan 2017 03:18:26 GMT

     [ https://issues.apache.org/jira/browse/LOG4J2-1784?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Ralph Goers updated LOG4J2-1784:
--------------------------------
    Issue Type: Improvement  (was: Bug)

> Large values for max in DefaultRolloverStrategy blocks application
> ------------------------------------------------------------------
>
>                 Key: LOG4J2-1784
>                 URL: https://issues.apache.org/jira/browse/LOG4J2-1784
>             Project: Log4j 2
>          Issue Type: Improvement
>          Components: Appenders
>    Affects Versions: 2.7
>         Environment: Played around a lot in 2.5, once realized issue was related to log4j,
upgraded to 2.7 and confirmed it is still happening.  Using on a raspberry pi.
>            Reporter: Charles Hache
>
> Hi all,
> I'm trying to debug an application which is using log4j2 for logging.  After discovering
that by default the RollingRandomAccessFile only kept the last 7 logs using the counter, I
found the DefaultRolloverStrategy option and set the max to something like 99999, so in theory
I wouldn't have to worry about it.
> A couple days later I started looking at everything again (log files from log4j, timestamped
CSV files from the application, etc) I can see something is going terribly wrong.  What I'm
finding is that when it comes time to rotate the logs, it looks like the whole application
hangs.  I see the following:
> - All logging to the log file stops;
> - All my data going to the CSV files stop;
> - CPU usage goes to 100%;
> - I cannot stop my application cleanly;
> After a while (~4-5 minutes) everything goes back to normal (until the next log rotation),
but then the first lines of the logs have timestamps like this:
> 2017-01-14 07:43:00,001 INFO ....
> 2017-01-14 07:42:11,329 DEBUG ....
> 2017-01-14 07:47:26,648 TRACE ....
> 2017-01-14 07:47:26,695 INFO ....
> 2017-01-14 07:47:26,697 TRACE ....
> 2017-01-14 07:47:26,737 INFO ....
> 2017-01-14 07:47:26,739 TRACE ....
> 2017-01-14 07:47:26,741 TRACE ....
> 2017-01-14 07:47:26,744 TRACE ....
> 2017-01-14 07:47:26,768 TRACE ....
> Of note is that there is a gap of a few minutes in the first couple lines of the file
(I'm not too concerned about the out-of-order timestamps as lots of different threads are
logging).  The application always writes many (dozens, maybe hundreds) of lines per second,
so a gap of a couple minutes is uncharacteristic.  The rest of the log file looks normal (has
no gaps, has log lines every few milliseconds).  From my specific log lines and where they
are w.r.t. each other, I looks to me like calls to the logger are blocking (eg: in cases I'll
have a couple log lines that usually log 1-2 milliseconds apart, but when they occur at rollover
time they'll be minutes apart).
> I shrunk the file size rollover to something small (256K), which I hit in maybe 15 seconds
or so, and it is clearly reproducible.  When I reduced the default rollover strategy max file
to 40, the problem when away and I can see it rolling over the file practically instantly.
> The documentation for the DefaultRolloverStrategy says "When the ascending attribute
is set to true (the default) then the counter will be incremented and the current log file
will be renamed to include the counter value. If the counter hits the maximum value then the
oldest file, which will have the smallest counter, will be deleted, all other files will be
renamed to have their counter decremented and then the current file will be renamed to have
the maximum counter value. Note that with this counting strategy specifying a large maximum
value may entirely avoid renaming files."
> I took this to mean that having a value so large that it would never be hit would be
more efficient, since it doesn't have to do anything, just keep counting up.  I'm wondering
now if it's doing something like "check if log-1.log exists... check if log-2.log exist .......
check if log-99999.log exists" but I don't see any iobound activity in iotop or anything (although
I can't say for sure if FS calls to see if something exists would show up there, for example).
> This might not necessarily be a bug in the logger per se, but it would at least be a
documentation issue if there is some O(n) operation based on the max value for the DefaultRolloverStrategy.
 
> I'd usually dig deeper, but now I still have to debug the original issues with the actual
application.  Let me know if there is any more info I should provide or if there is anything
else I can do!
> Thanks,
> Charles



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