The heap of application master is controlled
via yarn.app.mapreduce.am.command-opts and its default value is -Xmx1024m (
http://hadoop.apache.org/docs/stable/hadoop-mapreduce-client/hadoop-mapreduce-client-core/mapred-default.xml
).

yarn.scheduler.minimum-allocation-mb is completely different property -
http://hadoop.apache.org/docs/current/hadoop-yarn/hadoop-yarn-common/yarn-default.xml
The minimum allocation for every container request at the RM, in MBs.
Memory requests lower than this won't take effect, and the specified value
will get allocated at minimum.
2013/12/5 Vinod Kumar Vavilapalli <[EMAIL PROTECTED]>