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https://issues.apache.org/jira/browse/HADOOP-3110?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12582884#action_12582884
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Pete Wyckoff commented on HADOOP-3110:
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I'm seeing 11 microseconds for a small info log message with one variable and
one function call. And about .5 microseconds for it when the logging level is
error.
Maybe small here, but the hadoop synchronized methods aren't really in the
spirit of critical sections, but I'm happy to ignore this.
Of course, I don't know how long a typical call in the NN takes. If it's
something like 10 milliseconds, then this is too small to matter, but if 1 or
so, then this is starting to add up.
> 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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