Multiple Xmx Parameters to Java Process

When launching hadoop, the setting of environment variable HADOOP_HEAPMAX results in multiple Xmx parameters being passed to the java application launcher. This is because a default Xmx setting included in the HADOOP_CLIENT_OPTS in etc/hadoop/hadoop-env.sh, line 61:

# The following applies to multiple commands (fs, dfs, fsck, distcp etc)
export HADOOP_CLIENT_OPTS="-Xmx512m $HADOOP_CLIENT_OPTS"

is merged into the variable HADOOP_OPTS in bin/hadoop, line 160:

    # Always respect HADOOP_OPTS and HADOOP_CLIENT_OPTS
    HADOOP_OPTS="$HADOOP_OPTS $HADOOP_CLIENT_OPTS"

Orthogonally, the HADOOP_HEAPMAX environment variable triggers the setting of JAVA_HEAP_MAX in hadoop-config.sh, line 192:

# check envvars which might override default args
if [ "$HADOOP_HEAPSIZE" != "" ]; then
  #echo "run with heapsize $HADOOP_HEAPSIZE"
  JAVA_HEAP_MAX="-Xmx""$HADOOP_HEAPSIZE""m"
  #echo $JAVA_HEAP_MAX
fi

Which is ultimately passed to the java application launcher in bin/hadoop, line 166:

    exec "$JAVA" $JAVA_HEAP_MAX $HADOOP_OPTS $CLASS "$@"

The result: two Xmx settings passed to the Java application launcher. Which one is respected depends on the JVM, but for HotSpot the rightmost setting is respected, and so the HADOOP_HEAPMAX environment variable has no effect and the default setting in HADOOP_CLIENT_OPTS wins.