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https://issues.apache.org/jira/browse/LOG4J2-1784?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15884556#comment-15884556
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Ralph Goers commented on LOG4J2-1784:
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Any update on this?
> 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
> Assignee: Ralph Goers
>
> 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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