reducers

I have a five node cluster, three nodes of which contain DataNodes and TaskTrackers. I've imported around 10million rows from Oracle via Sqoop and process it via MapReduce in an Oozie workflow. The MapReduce job takes about 30 minutes and is only using one reducer. Edit - If I run the MapReduce code on its own, separate from Oozie, the job.setNumReduceTasks(4) correctly establishes 4 reducers. I have tried the following methods to manually set the number of reducers to four, with no success: In Oozie, set the following property in the tag of the map reduce node: <property><name>mapred.reduce

I have the following Reducer class public static class TokenCounterReducer extends Reducer<Text, Text, Text, Text> { public void reduce(Text key, Iterable<Text> values, Context context) throws IOException, InterruptedException { JSONObject jsn = new JSONObject(); for (Text value : values) { String[] vals = value.toString().split("\t"); String[] targetNodes = vals[0].toString().split(",",-1); jsn.put("source",vals[1] ); jsn.put("target",targetNodes); } // context.write(key, new Text(sum)); } } Going thru examples (disclaimer: newbie here), I can see that the general output type seems to be like

I followed Dan Abramov's code at https://github.com/tayiorbeii/egghead.io_redux_course_notes/blob/master/08-Reducer_Composition_with_Arrays.md I am getting error message "Unexpected token at line 22" referring to the ...todo Didn't think it's to do with Babel presets as ...state is working just fine. When I substitute ...todo with ...state inside the map function, it returns the same error. ///Reducer// export default (state=[], action) => { switch (action.type) { case 'ADD_TODO': return [...state, { id:action.id, text: action.text, completed:false } ]; case 'TOGGLE_TODO': return state.map

I have a reducer whereby I am retuning the appropriate state when an action is dispatched. Now I am calling an API at regular intervals so the result will trigger an action again and again. So what I want is that if the reducer state already has data then another reducer doesn't show the state as loading while the call is sent. It must maintain its loading state when receiving data the first time only. I hope I am able to explain it properly Here are my code snippets Loading state reducer const loading = (state = false, action) => { switch (action.type) { case 'GET_AUDIT_DATA': // here I want

In the MapReduce framework, one reducer is used for each key generated by the mapper. So you would think that specifying the number of Reducers in Hadoop MapReduce wouldn't make any sense because it's dependent on the program. However, Hadoop allows you to specify the number of reducers to use (-D mapred.reduce.tasks=# of reducers). What does this mean? Is the parameter value for number of reducers specifying how many machine resources go to the reducers instead of the number of actual reducers used? Judge Mental one reducer is used for each key generated by the mapper This comment is not

As given by Hadoop wiki to calculate ideal number of reducers is 0.95 or 1.75 * (nodes * mapred.tasktracker.tasks.maximum) but when to choose 0.95 and when 1.75? what is factor that considered while deciding this multiplier ? Let's say that you have 100 reduce slots available in your cluster. With a load factor of 0.95 all the 95 reduce tasks will start at the same time, since there are enough reduce slots available for all the tasks. This means that no tasks will be waiting in the queue, until one of the rest finishes. I would recommend this option when the reduce tasks are "small", i.e.,