How torunning nutch on 2G memory tasknode

[SunGod]

Error occurred in  "crawldb TestDB/crawldb" reduce phase

i get error msg --- java.lang.OutOfMemoryError: Java heap space

my command
 bin/nutch crawl url -dir TestDB -depth 4 -threads 3

 single fetchlist around in 200000

my settings on the memory

hadoop-env.sh
export HADOOP_HEAPSIZE=800

hadoop-site.xml
<property>
  <name>mapred.tasktracker.map.tasks.maximum</name>
  <value>4</value>
</property>
<property>
  <name>mapred.tasktracker.reduce.tasks.maximum</name>
  <value>4</value>
</property>
<property>
  <name>mapred.map.tasks</name>
  <value>2</value>
</property>
<property>
  <name>mapred.reduce.tasks</name>
  <value>2</value>
</property>
<property>
  <name>mapred.map.max.attempts</name>
  <value>4</value>
</property>
<property>
  <name>mapred.reduce.max.attempts</name>
  <value>4</value>
</property>
<property>
  <name>mapred.child.java.opts</name>
  <value>-Xmx250m</value>
</property>