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From "Owen O'Malley" <o...@yahoo-inc.com>
Subject Re: Configuration policy
Date Wed, 21 Jun 2006 15:55:09 GMT

On Jun 20, 2006, at 5:10 PM, Paul Sutter wrote:

> Thanks very much for the explanation, and to confirm I will repeat it:
>
> The first occurence of a parameter is used, and the search order is:
>
> hadoop-site.xml, then
> job.xml, then
> mapred-default.xml, then
> hadoop-default.xml
>
> Thats great, and it explains behavior that had been confusing before.

Exactly correct. One other piece that can cause confusion is that all 
of the files are found via the java class path. And they are present 
both in the conf directory in the distribution AND the hadoop-*.jar 
file.

One side effect of this is that I recommend never having a copy of 
hadoop-default.xml in your config directory. That is the one 
configuration file that you always want updated automatically when you 
update your distribution.

For the record, I like setting up my hadoop directories like:

$hadoop_prefix/hadoop-0.4-dev     # distribution directory
$hadoop_prefix/conf                          # local configuration
$hadoop_prefix/current                     # sym link over to the 
distribution directory
$hadoop_prefix/run/log                     # log directory
$hadoop_prefix/run/pid                     # pid directory
$hadoop_prefix/run/mapred             # map-reduce server directory
$hadoop_prefix/run/dfs/{data,name} # dfs server directories

-- Owen


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