You don't need to do all that work.
Just set:
<property>
<name>mapred.reduce.tasks</name>
<value>4</value>
<description>The default number of map tasks per job. Typically set
to a prime several times greater than number of available hosts.
Ignored when mapred.job.tracker is "local".
</description>
</property>
Either in hadoop-site or in your program using
conf.set("mapred.reduce.tasks", 4)
That will give you 4 reduce threads. You can have lots more than that if
you like.
On 10/3/07 6:50 PM, "Nguyen Manh Tien" <[EMAIL PROTECTED]> wrote:
> I know in Hadoop we can implement multi-threaded, asynchronous mapping with
> class MapRunnable. But this don't exist the similar class to do
> multi-threaded in reduce phrase. Could we do milti-thread in reduce phrase?.
> Does the following code work?
>
> public void reduce(WritableComparable key, Iterator values,
> OutputCollector output, Reporter reporter) {
> new SomeThread(output).start(); // transfer OutputCollector to thread
> }
>
> public class SomeThread extend Thread {
> OutputCollector ouput;
> public SomeThread(OutputCollector output) {
> this.output = output;
> }
> public void run() {
> output.collect(key, value);
> }
> }
