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https://issues.apache.org/jira/browse/LOG4J2-1784?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15823016#comment-15823016
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Ralph Goers edited comment on LOG4J2-1784 at 1/15/17 3:25 AM:
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Actually, this is a known problem and the documentation clearly tells you not
to do this. When the file rolls it looks for all the files it might have to
clean up so it looks for all the files between the min value and the max value
one by one. I have actually been working on an enhancement to the
RollingFileAppender and while reviewing this code realized that it could be
modified to use a DirectoryStream to get just the set of qualifying files to
look at. After I get my current enhancement working I might look into this one.
Actually, in looking at the documentation I notice that nothing is mentioned
there. The javadoc for the DefaultRolloverStrategy does say however, "Given
that this rollover algorithm requires as many file renaming operations as the
window size, large window sizes are discouraged.". The change I mentioned
above would do nothing to fix this, so if you really do get a large number of
files things would still get very slow.
was (Author: ralphgoers):
Actually, this is a known problem and the documentation clearly tells you not
to do this. When the file rolls it looks for all the files it might have to
clean up so it looks for all the files between the min value and the max value
one by one. I have actually been working on an enhancement to the
RollingFileAppender and while reviewing this code realized that it could be
modified to use a DirectoryStream to get just the set of qualifying files to
look at. After I get my current enhancement working I might look into this one.
> 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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