Sofia, You can access any HDFS file from a normal java application so long as your classpath and some configuration is set up correctly. That is all that the hadoop jar command does. It is a shell script that sets up the environment for java to work with Hadoop. Look at the example for the Tool Class
http://hadoop.apache.org/common/docs/current/api/org/apache/hadoop/util/Tool.html If you delete the JobConf stuff you can then just talk to the FIleSystem by doing the following Path p = new Path("URI OF FILE TO OPEN"); FileSystem fs = p.getFileSystem(conf); InputStream in = fs.open(p); Now you can use in to read your data. Just be sure to close it when you are done. --Bobby Evans On 7/25/11 4:40 PM, "Sofia Georgiakaki" <geosofie_...@yahoo.com> wrote: Good evening, I have built an Rtree on HDFS, in order to improve the query performance of high-selectivity spatial queries. The Rtree is composed of a number of hdfs files (each one created by one Reducer, so as the number of the files is equal to the number of the reducers), where each file is a subtree of the root of the Rtree. I investigate the way to use the Rtree in an efficient way, with respect to the locality of each file on hdfs (data-placement). I would like to ask, if it is possible to read a file which is on hdfs, from a java application (not MapReduce). In case this is not possible (as I believe), either I should download the files on the local filesystem (which is not a solution, since the files could be very large), orrun the queries using the Hadoop. In order to maximise the gain, I should probably process a batch of queries during each Job, and run each query on a node that is "near" to the files that are involved in handling the specific query. Can I find the node where each file is located (or at least most of its blocks), and run on that node a reducer that handles these queries? Could the function DFSClient.getBlockLocations() help ? Thank you in advance, Sofia
