The wordcount example, by default, will run a single reducer. This is
controllable by passing -Dmapred.reduce.tasks=2 to your launcher. The
following will work:
hadoop jar hadoop-examples.jar wordcount -Dmapred.reduce.tasks=2 input output
Note that just cause a cluster has N nodes, N reducers aren't
necessary to run. It is not dependent on such things, and is simply a
user-configurable number with the default value of 1.
On Tue, Sep 6, 2011 at 3:23 PM, john smith <[EMAIL PROTECTED]> wrote:
> Yep , it works .. I just synced /etc/hosts files and I didnt change other
> configs and now its working fine. Thanks for the help Harsh. Sorry for
> spamming without checking my TTlogs properly.
> Also 1 more doubt . Any idea why its scheduling only a single reduce? I have
> 2 datanodes and I am expecting it to run 2 reducers (data size of 500MB) .
> Any hints?
> On Tue, Sep 6, 2011 at 3:17 PM, Harsh J <[EMAIL PROTECTED]> wrote:
>> Yes, looks like your slave nodes aren't able to properly resolve some
>> hostnames. Hadoop requires a sane network setup to work properly.
>> Also, yes, you need to use a hostname for your fs.default.name and
>> other configs to the extent possible.
>> The easiest way is to keep a properly synchronized /etc/hosts file.
>> For example, it may look like so, on all machines:
>> 127.0.0.1 localhost.localdomain localhost
>> 192.168.0.1 master.hadoop master
>> 192.168.0.2 slave3.hadoop slave3
>> (and so on…)
>> (This way master can resolve slaves, and slaves can resolve master. If
>> you have the time, setup a DNS, its the best thing to do.)
>> Then, in core-site.xml you'll need:
>> fs.default.name = hdfs://master
>> And in mapred-site.xml:
>> mapred.job.tracker = master:8021
>> That should do it, so long as the slave hosts can freely access the
>> master hosts (no blockage of ports via firewall and such).
>> On Tue, Sep 6, 2011 at 3:05 PM, john smith <[EMAIL PROTECTED]> wrote:
>> > Hey My TT logs show this ,
>> > 2011-09-06 13:22:41,860 ERROR org.apache.hadoop.mapred.TaskTracker:
>> > exception: java.net.UnknownHostException: unknown host: rip-pc.local
>> > at org.apache.hadoop.ipc.Client$Connection.<init>(Client.java:195)
>> > at org.apache.hadoop.ipc.Client.getConnection(Client.java:853)
>> > at org.apache.hadoop.ipc.Client.call(Client.java:723)
>> > at org.apache.hadoop.ipc.RPC$Invoker.invoke(RPC.java:220)
>> > at $Proxy5.getProtocolVersion(Unknown Source)
>> > at org.apache.hadoop.ipc.RPC.getProxy(RPC.java:359)
>> > at org.apache.hadoop.hdfs.DFSClient.createRPCNamenode(DFSClient.java:106)
>> > at org.apache.hadoop.hdfs.DFSClient.<init>(DFSClient.java:207)
>> > at org.apache.hadoop.hdfs.DFSClient.<init>(DFSClient.java:170)
>> > at
>> > ^C at
>> > at org.apache.hadoop.fs.FileSystem.access$200(FileSystem.java:66)
>> > at org.apache.hadoop.fs.FileSystem$Cache.get(FileSystem.java:1390)
>> > at org.apache.hadoop.fs.FileSystem.get(FileSystem.java:196)
>> > May be some error in configs ?? I am using IPs in the conf files ..should
>> > put entries in /etc/hosts files?
>> > On Tue, Sep 6, 2011 at 3:00 PM, john smith <[EMAIL PROTECTED]>
>> >> Hi Harsh,
>> >> My jt log : http://pastebin.com/rXAEeDkC
>> >> I have some startup exceptions (which doesn't matter much I guess) but
>> >> tail indicates that its locating the splits correctly and then it hangs
>> >> Any idea?
>> >> Thanks
>> >> On Tue, Sep 6, 2011 at 1:30 PM, Harsh J <[EMAIL PROTECTED]> wrote:
>> >>> I'd check the tail of JobTracker logs after a submit is done to see if
>> >>> an error/warn there is causing this. And then dig further on
>> >>> why/what/how.
>> >>> Hard to tell what your problem specifically is without logs :)