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From "Tsz Wo (Nicholas), SZE (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HDFS-1320) Add LOG.isDebugEnabled() guard for each LOG.debug("...")
Date Thu, 19 Aug 2010 21:58:17 GMT

    [ https://issues.apache.org/jira/browse/HDFS-1320?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12900484#action_12900484
] 

Tsz Wo (Nicholas), SZE commented on HDFS-1320:
----------------------------------------------

> does the JVM not optimize for this case in the fast-path? 

Hi Ryan, from the benchmark results [here|https://issues.apache.org/jira/browse/HADOOP-6884?focusedCommentId=12900087&page=com.atlassian.jira.plugin.system.issuetabpanels%3Acomment-tabpanel#action_12900087],
it does not seem JVM optimized this.  I think JVM cannot do anything in general since parameter
evaluation may have side-effect.  It is hard for the JVM to determine whether it is safe to
skip those instructions.

> Add LOG.isDebugEnabled() guard for each LOG.debug("...")
> --------------------------------------------------------
>
>                 Key: HDFS-1320
>                 URL: https://issues.apache.org/jira/browse/HDFS-1320
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>    Affects Versions: 0.22.0
>            Reporter: Erik Steffl
>            Assignee: Erik Steffl
>             Fix For: 0.22.0
>
>         Attachments: HDFS-1320-0.22-1.patch, HDFS-1320-0.22-2.patch, HDFS-1320-0.22.patch
>
>
> Each LOG.debug("...") should be executed only if LOG.isDebugEnabled() is true, in some
cases it's expensive to construct the string that is being printed to log. It's much easier
to always use LOG.isDebugEnabled() because it's easier to check (rather than in each case
reason wheather it's neccessary or not).

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