If you want to use NLineInputFormat, and also want the individual file to be processed in the map task which prefer to be on the same task node as data node, you need to implement and control that kind of logic by yourself. Extend the NLineInputFormat, Override the getSplits() method, read the location of the HDFS file, and assign the server of the same file/block. Keep in mind that NLineInputFormat will send one file to one mapper. So you need to make sure that the file size is less than one block, Split is on block level instead of file. About detail how to control the Mapper execution location, you can refer this book: Professional Hadoop Solution http://www.amazon.com/Professional-Hadoop-Solutions-Boris-Lublinsky/dp/1118611934/ref=sr_1_1?s=books&ie=UTF8&qid=1408644908&sr=1-1&keywords=hadoop+solution Chapter 4 Customizing MapReduce Execution describes some examples how to do that. Yong
Date: Thu, 21 Aug 2014 22:26:12 +0530 Subject: Re: Hadoop InputFormat - Processing large number of small files From: [email protected] To: [email protected] Hello, This means that a file with names of all the files that need to be processed and is fed to hadoop with NLineInputFormat? If this is the case, then, how can we ensure that map processes are scheduled in the node where blocks containing the files are stored already? regardsrab On Thu, Aug 21, 2014 at 9:07 PM, Felix Chern <[email protected]> wrote: If I were you, I’ll first generate a file with those file name: hadoop fs -ls > term_file Then run the normal map reduce job Felix On Aug 21, 2014, at 1:38 AM, rab ra <[email protected]> wrote: Thanks for the link. If it is not required for CFinputformat to have contents of the files in the map process but only the filename, what changes need to be done in the code? rab. On 20 Aug 2014 22:59, "Felix Chern" <[email protected]> wrote: I wrote a post on how to use CombineInputFormat:http://www.idryman.org/blog/2013/09/22/process-small-files-on-hadoop-using-combinefileinputformat-1/ In the RecordReader constructor, you can get the context of which file you are reading in.In my example, I created FileLineWritable to include the filename in the mapper input key.Then you can use the input key as: public static class TestMapper extends Mapper<FileLineWritable, Text, Text, IntWritable>{ private Text txt = new Text(); private IntWritable count = new IntWritable(1); public void map (FileLineWritable key, Text val, Context context) throws IOException, InterruptedException{ StringTokenizer st = new StringTokenizer(val.toString()); while (st.hasMoreTokens()){ txt.set(key.fileName + st.nextToken()); context.write(txt, count); } } } Cheers,Felix On Aug 20, 2014, at 8:19 AM, rab ra <[email protected]> wrote: Thanks for the response. Yes, I know wholeFileInputFormat. But i am not sure filename comes to map process either as key or value. But, I think this file format reads the contents of the file. I wish to have a inputformat that just gives filename or list of filenames. Also, files are very small. The wholeFileInputFormat spans one map process per file and thus results huge number of map processes. I wish to span a single map process per group of files. I think I need to tweak CombineFileInputFormat's recordreader() so that it does not read the entire file but just filename. regardsrab regardsBala On Wed, Aug 20, 2014 at 6:48 PM, Shahab Yunus <[email protected]> wrote: Have you looked at the WholeFileInputFormat implementations? There are quite a few if search for them... http://hadoop-sandy.blogspot.com/2013/02/wholefileinputformat-in-java-hadoop.html https://github.com/tomwhite/hadoop-book/blob/master/ch07/src/main/java/WholeFileInputFormat.java Regards,Shahab On Wed, Aug 20, 2014 at 1:46 AM, rab ra <[email protected]> wrote: Hello, I have a use case wherein i need to process huge set of files stored in HDFS. Those files are non-splittable and they need to be processed as a whole. Here, I have the following question for which I need answers to proceed further in this. 1. I wish to schedule the map process in task tracker where data is already available. How can I do it? Currently, I have a file that contains list of filenames. Each map get one line of it via NLineInputFormat. The map process then accesses the file via FSDataInputStream and work with it. Is there a way to ensure this map process is running on the node where the file is available?. 2. Since the files are not large and it can be called as 'small' files by hadoop standard. Now, I came across CombineFileInputFormat that can process more than one file in a single map process. What I need here is a format that can process more than one files in a single map but does not have to read the files, and either in key or value, it has the filenames. In map process then, I can run a loop to process these files. Any help? 3. Any othe alternatives? regards rab
