[jira] Commented: (HADOOP-3110) NameNode does logging in critical sections just about everywhere

["Raghu Angadi (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HADOOP-3110?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12582795#action_12582795 ] 

Raghu Angadi commented on HADOOP-3110:
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Pretty much everything that FSNamesystem (ie. pretty much all that NameNode does) is under one lock, of course including these logs. This one global lock has been under the discussion for quite sometime.

Do you have any benchmark numbers that show any improvement when we comment out these log statements? Benchmark of either realistic load or artificial load is fine. 

To use async logger you mentioned, is it just a matter of changing log4j.properties?

> 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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