The Hadoop command line scripts (hadoop.sh or hadoop.cmd) will call java with "-Xmx" options twice. The impact is that any user defined HADOOP_HEAP_SIZE env variable will take no effect because it is overwritten by the second "-Xmx" option.
For example, here is the java cmd generated for command "hadoop fs -ls /", Notice that there are two "-Xmx" options: "-Xmx1000m" and "-Xmx512m" in the command line:
java -Xmx1000m -Dhadoop.log.dir=C:\tmp\logs -Dhadoop.log.file=hadoop.log -Dhadoop.root.logger=INFO,c
onsole,DRFA -Xmx512m -Dhadoop.security.logger=INFO,RFAS -classpath XXX org.apache.hadoop.fs.FsShell -ls /
Here is the root cause:
The call flow is: hadoop.sh calls hadoop_config.sh, which in turn calls hadoop-env.sh.
In hadoop.sh, the command line is generated by the following pseudo code:
java $JAVA_HEAP_MAX $HADOOP_CLIENT_OPTS -classpath ...
In hadoop-config.sh, $JAVA_HEAP_MAX is initialized as "-Xmx1000m" if user didn't set $HADOOP_HEAP_SIZE env variable.
In hadoop-env.sh, $HADOOP_CLIENT_OPTS is set as this:
export HADOOP_CLIENT_OPTS="-Xmx512m $HADOOP_CLIENT_OPTS"
To fix this problem, we should remove the "-Xmx512m" from HADOOP_CLIENT_OPTS. If we really want to change the memory settings we need to use $HADOOP_HEAP_SIZE env variable.