how to update config parameter of hadoop mapred-site.xml without restarting the cluster

Question:

I would like to add/update the following parameter

<property>
    <name>mapred.map.tasks.speculative.execution</name>
    <value>false</value>
</property>

in mapred-site.xml in hadoop. How can I do this without restarting the cluster?

Answer:

You can set this per-job in your job's configuration. If you want to change this behaviour globally you have to restart your cluster. There is no way to change it without restarting.