There are two important configuration files in a Hadoop cluster:
<li><strong>Default Configuration</strong>: There are core-default.xml, hdfs-default.xml and mapred-default.xml files in which we specify the default configuration for Hadoop cluster. These are read only files.</li> <li><strong>Custom Configuration</strong>: We have site-specific custom files like core-site.xml, hdfs-site.xml, mapred-site.xml in which we can specify the site-specific configuration.
All the Jobs in Hadoop and HDFS implementation uses the parameters defined in the above-mentioned files. With customization we can tune these processes according to our use case.
In Hadoop API, there is a Configuration class that loads these files and provides the values at run time to different jobs.