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Date: Tue, 17 Aug 2010 12:41:17 -0400 (EDT)
From: "Luke Lu (JIRA)" <jira@apache.org>
To: common-issues@hadoop.apache.org
Subject: [jira] Commented: (HADOOP-6884) Add LOG.isDebugEnabled() guard for
 each LOG.debug("...")
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    [ https://issues.apache.org/jira/browse/HADOOP-6884?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12899461#action_12899461 ] 

Luke Lu commented on HADOOP-6884:
---------------------------------

Did some digging on the aspectj wrapping approach. Looks like it's a no go performance wise, as it cannot solve the arguments building cost issue without fixing aspectj itself, as someone else tried to do exactly the same thing here:

http://dev.eclipse.org/mhonarc/lists/aspectj-users/msg09294.html

Looks the most reasonable current course of action is just committing the patch as it looks correct, low risk and significantly lower gc stress (especially in namenode code, according to Suresh in offline discussions.) 

We should file a separate jira to explore the switching to slf4j api (still using log4j as backend) approach. One open issue even with slf4j API is that it doesn't solve the autoboxing cost issue for primitive types, which we use a lot the logs:

http://qos.ch/pipermail/slf4j-dev/2005-August/000241.html (old but still reflecting the current API design.)

> Add LOG.isDebugEnabled() guard for each LOG.debug("...")
> --------------------------------------------------------
>
>                 Key: HADOOP-6884
>                 URL: https://issues.apache.org/jira/browse/HADOOP-6884
>             Project: Hadoop Common
>          Issue Type: Improvement
>    Affects Versions: 0.22.0
>            Reporter: Erik Steffl
>            Assignee: Erik Steffl
>             Fix For: 0.22.0
>
>         Attachments: HADOOP-6884-0.22-1.patch, HADOOP-6884-0.22.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 whether it's necessary or not).

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