hadoop memory settings

[Visioner Sadak]

Is ther a relation between HADOOP_HEAPSIZE mapred.child.java.opts and
mapred.child.ulimit settings in hadoop-env.sh and mapred-site.xml i have a
sinngle machine with 2gb ram and running hadoop on psuedo distr mode my
HADOOP_HEAPSIZE is set to 256 wat shud i set mapred.child.java.opts and
mapred.child.ulimit and how these settings are calculated if my ram is
incresed or machine clusters are increased