Re: isSplitable() problem
I have chosen to use Jay's suggestion as a quick workaround and am pleased to report that it seems to work well on small test inputs. My question now is, are the mappers guaranteed to receive the file's lines in order? Browsing the source suggests this is so, but I just want to make sure as my understanding of Hadoop is transubstantial. Thank you for your patience in answering my questions. On 23 April 2012 14:28, Harsh J ha...@cloudera.com wrote: Jay, On Mon, Apr 23, 2012 at 6:43 PM, JAX jayunit...@gmail.com wrote: Curious : Seems like you could aggregate the results in the mapper as a local variable or list of strings--- is there a way to know that your mapper has just read the LAST line of an input split? True. Can be one way to do it (unless aggregation of 'records' needs to happen live, and you don't wish to store it all in memory). Is there a cleanup or finalize method in mappers that is run at the end of a whole steam read to support these sort of chunked, in memor map/r operations? Yes there is. See: Old API: http://hadoop.apache.org/common/docs/r0.20.2/api/org/apache/hadoop/mapred/Mapper.html (See Closeable's close()) New API: http://hadoop.apache.org/common/docs/r0.20.2/api/org/apache/hadoop/mapreduce/Mapper.html#cleanup(org.apache.hadoop.mapreduce.Mapper.Context) -- Harsh J
isSplitable() problem
I require each input file to be processed by each mapper as a whole. I subclass c.o.a.h.mapreduce.lib.input.TextInputFormat and override isSplitable() to invariably return false. The job is configured to use this subclass as the input format class via setInputFormatClass(). The job runs without error, yet the logs reveal files are still processed line by line by the mappers. Any help would be greatly appreciated, Thanks
Re: isSplitable() problem
Thanks for the clarification. On 23 April 2012 12:52, Harsh J ha...@cloudera.com wrote: Dan, Split and reading a whole file as a chunk are two slightly different things. The former controls if your files ought to be split across mappers (useful if there are multiple blocks of file in HDFS). The latter needs to be achieved differently. The TextInputFormat provides by default a LineRecordReader, which as it name goes - reads whatever stream is provided to it line-by-line. This is regardless of the file's block splits (a very different thing than line splits). You need to implement your own RecordReader and return it from your InputFormat to do what you want it to - i.e. read the whole stream into an object and then pass it out to the Mapper. On Mon, Apr 23, 2012 at 5:10 PM, Dan Drew wirefr...@googlemail.com wrote: I require each input file to be processed by each mapper as a whole. I subclass c.o.a.h.mapreduce.lib.input.TextInputFormat and override isSplitable() to invariably return false. The job is configured to use this subclass as the input format class via setInputFormatClass(). The job runs without error, yet the logs reveal files are still processed line by line by the mappers. Any help would be greatly appreciated, Thanks -- Harsh J
