hadoop-mapreduce-dev mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From Daniel Templeton <dan...@cloudera.com>
Subject Re: Map reduce sample program
Date Tue, 22 Aug 2017 18:22:01 GMT
On 8/19/17 3:28 AM, Remil Mohanan wrote:
> I am trying to pass multiple non key values from mapper to reducer.

The only way to pass data from the mapper to the reducer is through 
passing key-values.  One common trick is to designate a special key as 
the out-of-band information key and then use a custom sorting comparator 
to make sure that key comes first in the sort order.  I'm sure you can 
find examples online.

> Similarly for reading and writing a file inside the hdfs system other than normal read
and write.

I don't understand.  Reading and writing a file in HDFS from an MR task 
works exactly the same as doing it from a stand-alone program. You 
probably want to do it in the setup() method, though.


To unsubscribe, e-mail: mapreduce-dev-unsubscribe@hadoop.apache.org
For additional commands, e-mail: mapreduce-dev-help@hadoop.apache.org

View raw message