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https://issues.apache.org/jira/browse/HADOOP-3110?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12583136#action_12583136
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Doug Cutting commented on HADOOP-3110:
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> Of course, I think it is worthwhile to open a JIRA around the general issue
> that critical sections are not treated as such in many places.
This seems too general for a JIRA issue. General coding guidelines and
principles are more appropriate on the wiki, no?
The ideal performance-related JIRA describes a measurable problem. Then
specific solutions can be evaluated. So if, for example, you think
synchronized logging is significantly affecting namenode performance (as you
seem to) then that's something we can measure and fix. So let's measure it
first, and if it's indeed significant, let's fix it. Since others seem to
question whether this is in fact significant, I suggested that the task of
measuring it was yours, as this would probably convince others it was worth
fixing. Does that make sense?
> 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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