# MapReduce Settings

# Check Memory

Check available server memory.

cat /proc/meminfo | grep "MemTotal"

If the server has less than 8 GB of available physical memory, do not modify the default settings.

# Increase Memory Allocations

Edit /opt/atsd/hadoop/etc/hadoop/mapred-site.xml file.

• Set mapreduce.map.memory.mb and mapreduce.reduce.memory.mb to 50% of the available memory.

• Set mapreduce.map.java.opts and mapreduce.reduce.java.opts to 80% of mapreduce.map.memory.mb and mapreduce.reduce.memory.mb.

Sample memory configuration for a server with 16 GB of RAM:

<property>
    <name>mapreduce.map.memory.mb</name>
    <!-- must not exceed 50% of available physical memory on the server -->
    <value>8000</value>
</property>
<property>
    <name>mapreduce.map.java.opts</name>
    <!-- set to 80% of mapreduce.map.memory.mb -->
    <value>-Xmx5600m</value>
</property>
<property>
    <name>mapreduce.reduce.memory.mb</name>
    <!-- must not exceed 50% of available physical memory on the server -->
    <value>8000</value>
</property>
<property>
    <!-- set to 80% of mapreduce.reduce.memory.mb -->
    <name>mapreduce.reduce.java.opts</name>
    <value>-Xmx5600m</value>
</property>