[ http://issues.apache.org/jira/browse/HADOOP-372?page=comments#action_12427768 ] Runping Qi commented on HADOOP-372: -----------------------------------
It would be great if we make it optional for the user to specify key/value classes for the inputs. Theses classes, if specified by the user, would be used for validation check only. That way, the framework will get the input key/value class info from the the input files alone. That will be very robust. Assuming that all records in each split will have the same key/value classes, then the framework can determine the appropriate mapper class upfront, and call the map function of that mapper class, thus the map function does not need to call instanceof method. The split will not be static. The only constraint is that a split will not span across multiple files, which is true now. > should allow to specify different inputformat classes for different input > dirs for Map/Reduce jobs > -------------------------------------------------------------------------------------------------- > > Key: HADOOP-372 > URL: http://issues.apache.org/jira/browse/HADOOP-372 > Project: Hadoop > Issue Type: New Feature > Components: mapred > Affects Versions: 0.4.0 > Environment: all > Reporter: Runping Qi > > Right now, the user can specify multiple input directories for a map reduce > job. > However, the files under all the directories are assumed to be in the same > format, > with the same key/value classes. This proves to be a serious limit in many > situations. > Here is an example. Suppose I have three simple tables: > one has URLs and their rank values (page ranks), > another has URLs and their classification values, > and the third one has the URL meta data such as crawl status, last crawl > time, etc. > Suppose now I need a job to generate a list of URLs to be crawled next. > The decision depends on the info in all the three tables. > Right now, there is no easy way to accomplish this. > However, this job can be done if the framework allows to specify different > inputformats for different input dirs. > Suppose my three tables are in the following directory respectively: > rankTable, classificationTable. and metaDataTable. > If we extend JobConf class with the following method (as Owen suggested to > me): > addInputPath(aPath, anInputFormatClass, anInputKeyClass, > anInputValueClass) > Then I can specify my job as follows: > addInputPath(rankTable, SequenceFileInputFormat.class, UTF8.class, > DoubleWritable.class) > addInputPath(classificationTable, TextInputFormat.class, UTF8,class, > UTF8.class) > addInputPath(metaDataTable, SequenceFileInputFormat.class, UTF8.class, > MyRecord.class) > If an input directory is added through the current API, it will have the same > meaning as it is now. > Thus this extension will not affect any applications that do not need this > new feature. > It is relatively easy for the M/R framework to create an appropriate record > reader for a map task based on the above information. > And that is the only change needed for supporting this extension. -- 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
