1
除了map函數輸出的所有鍵都相同之外,什麼會導致MapReduce作業中只有一個Reducer?MapReduce低效減速器
除了map函數輸出的所有鍵都相同之外,什麼會導致MapReduce作業中只有一個Reducer?MapReduce低效減速器
可能的原因:
<property>
<name>mapred.reduce.tasks</name>
<value>1</value>
<description>The default number of reduce tasks per job. Typically set to 99%
of the cluster's reduce capacity, so that if a node fails the reduces can
still be executed in a single wave.
Ignored when mapred.job.tracker is "local".
</description>
</property>