Hi, @Harsh: Thanks for the reply. Would the patch work in Hadoop 1.0.4 release?
-----Original Message----- From: Harsh J [mailto:[email protected]] Sent: Monday, May 13, 2013 1:03 PM To: <[email protected]> Subject: Re: How to combine input files for a MapReduce job For "control number of mappers" question: You can use http://hadoop.apache.org/docs/current/api/org/apache/hadoop/mapred/lib/CombineFileInputFormat.html which is designed to solve similar cases. However, you cannot beat the speed you get out of a single large file (or a few large files), as you'll still have file open/close overheads which will bog you down. For "which file is being submitted to which" question: Having https://issues.apache.org/jira/browse/MAPREDUCE-3678 in the version/distribution of Apache Hadoop you use would help. On Mon, May 13, 2013 at 12:50 PM, Agarwal, Nikhil <[email protected]> wrote: > Hi, > > > > I have a 3-node cluster, with JobTracker running on one machine and > TaskTrackers on other two. Instead of using HDFS, I have written my > own FileSystem implementation. As an experiment, I kept 1000 text > files (all of same size) on both the slave nodes and ran a simple > Wordcount MR job. It took around 50 mins to complete the task. > Afterwards, I concatenated all the > 1000 files into a single file and then ran a Wordcount MR job, it took > 35 secs. From the JobTracker UI I could make out that the problem is > because of the number of mappers that JobTracker is creating. For 1000 > files it creates > 1000 maps and for 1 file it creates 1 map (irrespective of file size). > > > > Thus, is there a way to reduce the number of mappers i.e. can I > control the number of mappers through some configuration parameter so > that Hadoop would club all the files until it reaches some specified > size (say, 64 MB) and then make 1 map per 64 MB block? > > > > Also, I wanted to know how to see which file is being submitted to > which TaskTracker or if that is not possible then how do I check if > some data transfer is happening in between my slave nodes during a MR job? > > > > Sorry for so many questions and Thank you for your time. > > > > Regards, > > Nikhil -- Harsh J
