[ http://issues.apache.org/jira/browse/HADOOP-115?page=comments#action_12372801 ]
Teppo Kurki commented on HADOOP-115: ------------------------------------ " I.e., the input keys and values are drawn from a different domain than the output keys and values. Furthermore, the intermediate keys and values are from the same domain as the output keys and values. " The Google MapReduce paper states the Web-Link graph example where this is not the case: "Reverse Web-Link Graph: The map function outputs (target; source) pairs for each link to a target URL found in a page named source. The reduce function concatenates the list of all source URLs associated with a given target URL and emits the pair: (target; list(source))". > Hadoop should allow the user to use SequentialFileOutputformat as the output > format and to choose key/value classes that are different from those for map > output. > ------------------------------------------------------------------------------------------------------------------------------------------------------------------ > > Key: HADOOP-115 > URL: http://issues.apache.org/jira/browse/HADOOP-115 > Project: Hadoop > Type: Improvement > Components: mapred > Reporter: Runping Qi > > When map tasks write intermediate data out, they always use SequencialFile > RecordWriter with key/value classes from the job object. > When the reducers write the final results out, its output format is obtained > from the job object. By default, it is TextOutputFormat, and no conflicts. > However, if one wants to use SequencialFileFormat for the final results, then > the key/value classes are also obtained from the job object, the same as the > map tasks' output. Now we have a problem. It is impossible for the map > outputs and reducer outputs use different key/value classes, if one wants the > reducers generate outputs in SequentialFileFormat. > A simple fix would be to add another two attributes to JobConf class: > mapOutputLeyClass and mapOutputValueClass. That allows the user to have > different key/value classes for the intermediate and final outputs. -- This message is automatically generated by JIRA. - If you think it was sent incorrectly contact one of the administrators: http://issues.apache.org/jira/secure/Administrators.jspa - For more information on JIRA, see: http://www.atlassian.com/software/jira
