Home | About | Sematext search-lucene.com search-hadoop.com
NEW: Monitor These Apps!
elasticsearch, apache solr, apache hbase, hadoop, redis, casssandra, amazon cloudwatch, mysql, memcached, apache kafka, apache zookeeper, apache storm, ubuntu, centOS, red hat, debian, puppet labs, java, senseiDB
 Search Hadoop and all its subprojects:

Switch to Threaded View
MapReduce >> mail # user >> Stupid questions about combiners in ...hadoop.mapreduce


Copy link to this message
-
Re: Stupid questions about combiners in ...hadoop.mapreduce
Questions 2 and 3 can be answered relatively easily:
Remember, the output of the combiner is going to be consumed by the reducer.
So the output key/vlaue classes of the combiner have to align with the input
key/vlaue classes of the reducer.

On Mon, May 23, 2011 at 11:32 AM, Mike Spreitzer <[EMAIL PROTECTED]>wrote:

> In general, the Java interfaces say that one invocation of a combiner
> (technically, a Class<? *extends* Reducer>) can output multiple
> (key,value) pairs.  So:
>
> What happens if one invocation of a combiner outputs more than one value?
>
> What happens if an output key is different from the input key?
>
> What happens if an output value is of a different class than the class of
> the input values?
>
> Thanks,
> Mike Spreitzer
>
NEW: Monitor These Apps!
elasticsearch, apache solr, apache hbase, hadoop, redis, casssandra, amazon cloudwatch, mysql, memcached, apache kafka, apache zookeeper, apache storm, ubuntu, centOS, red hat, debian, puppet labs, java, senseiDB