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https://issues.apache.org/jira/browse/HADOOP-3110?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12583156#action_12583156
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Pete Wyckoff commented on HADOOP-3110:
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I think the 11 microseconds/logged call and the 0.5-1 microsecond per non
logged call (e.g., a debug call with debug logging disabled) is probably
negligible in the critical sections. And since everyone doesn't make an actual
log call that gets logged the avg total per call is probably about 10
microseconds. (each call may go through a number of debug logs + some calls
actually log and do the debug things).
So, I think we can close this issue. Unless there are calls that involved
complex formatting and lots of other function calls to do that formatting, I
don't think it's a problem. And I don't see any calls like that. And obviously
we aren't ever using patterns that log4j sucks on - i.e., ones with file,
method or line # info, it's safe to say it's a non-issue.
> NameNode does logging in critical sections just about everywhere
> ----------------------------------------------------------------
>
> Key: HADOOP-3110
> URL: https://issues.apache.org/jira/browse/HADOOP-3110
> Project: Hadoop Core
> Issue Type: Improvement
> Components: dfs
> Affects Versions: 0.14.0, 0.14.1, 0.14.2, 0.14.3, 0.14.4, 0.15.0, 0.15.1,
> 0.15.2, 0.15.3, 0.16.0, 0.16.1
> Environment: All
> Reporter: Pete Wyckoff
>
> e.g., FSNameSystem.addStoredBlock (but almost every method has logging in its
> critical sections)
> This method is synchronized and it's spitting something out to Log.info every
> block stored. Normally not a big deal, but since this is in the name node and
> these are critical sections...
> We shouldn't even do any logging at all in critical sections, so even the
> info and warn are bad. But, in many places in the code, it would be hard to
> tease these out (although eventually they really should be), but the system
> could start using something like an AsyncAppender and see how it improves
> performance.
> Even though the log may have a buffer, the writing and doing the formatting
> and stuff cause a drag on performance with 100s/1000s of machines trying to
> talk to the name node.
> At a minimum, the most often triggered Log.info could be changed to
> Log.debug.
> for reference:
> http://logging.apache.org/log4j/1.2/apidocs/org/apache/log4j/AsyncAppender.html
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