Vishal Shah wrote: > Hi, > > While running a fetch on 3M urls with -noParsing option set, I noticed > that the reduce is taking too long. Since the reducer class is the > IdentityReducer class in this case, couldn't hadoop handle it internally > by setting the output path of map directly to the final output path? Or, > do a simple rename of the temp output directory to the final output > directory? > > For the reduce phase, it seems that the copy is unnecessary in this > case. I am unfamiliar with the details of Hadoop, so maybe there is a > strong reason to do things the way they are done right now, or maybe I > am mistaken about how they are done. Can the experts please throw some > light on this? > >
Unfortunately, it's not possible - partial outputs from map tasks are basically in random key order, and need to be sorted in order to produce output MapFile-s. IdentityReducer indeed does nothing, but the ReduceTask framework is doing the sorting ... Do you think the copy/sort phase is a performance bottleneck in your case? You could try changing the number of reduce tasks, or perhaps the number of tasks per tasktracker - please see http://wiki.apache.org/lucene-hadoop/HowManyMapsAndReduces for more details. -- Best regards, Andrzej Bialecki <>< ___. ___ ___ ___ _ _ __________________________________ [__ || __|__/|__||\/| Information Retrieval, Semantic Web ___|||__|| \| || | Embedded Unix, System Integration http://www.sigram.com Contact: info at sigram dot com ------------------------------------------------------------------------- Using Tomcat but need to do more? Need to support web services, security? Get stuff done quickly with pre-integrated technology to make your job easier Download IBM WebSphere Application Server v.1.0.1 based on Apache Geronimo http://sel.as-us.falkag.net/sel?cmd=lnk&kid=120709&bid=263057&dat=121642 _______________________________________________ Nutch-general mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/nutch-general
