title: Hadoop slows down after map 100%
body: <p>I am running a test on a 5 node cluster, on hadoop 1.0.3. The test consists of a chain of 3 jobs. The first job runs perfectly. The second job takes the output of the first job (around 100MB). After the mapping smoothly gets to a 100%, the job gets stuck in between the map phase and the reduce phase. It takes a lot of time to get the reduce to 5%. Here's the complete Hadoop output with the times.</p>
  
  <pre><code>13/11/19 13:39:25 INFO mapred.JobClient:  map 0% reduce 0%
  13/11/19 13:40:12 INFO mapred.JobClient:  map 1% reduce 0%
  13/11/19 13:40:20 INFO mapred.JobClient:  map 2% reduce 0%
  13/11/19 13:40:24 INFO mapred.JobClient:  map 3% reduce 0%
  13/11/19 13:40:29 INFO mapred.JobClient:  map 4% reduce 0%
  13/11/19 13:40:39 INFO mapred.JobClient:  map 5% reduce 0%
  13/11/19 13:40:42 INFO mapred.JobClient:  map 6% reduce 0%
  13/11/19 13:40:51 INFO mapred.JobClient:  map 7% reduce 0%
  13/11/19 13:41:01 INFO mapred.JobClient:  map 8% reduce 0%
  13/11/19 13:41:06 INFO mapred.JobClient:  map 9% reduce 0%
  13/11/19 13:41:18 INFO mapred.JobClient:  map 10% reduce 0%
  13/11/19 13:41:22 INFO mapred.JobClient:  map 11% reduce 0%
  13/11/19 13:41:33 INFO mapred.JobClient:  map 12% reduce 0%
  13/11/19 13:41:42 INFO mapred.JobClient:  map 13% reduce 0%
  13/11/19 13:41:50 INFO mapred.JobClient:  map 14% reduce 0%
  13/11/19 13:41:55 INFO mapred.JobClient:  map 15% reduce 0%
  13/11/19 13:42:04 INFO mapred.JobClient:  map 16% reduce 0%
  13/11/19 13:42:11 INFO mapred.JobClient:  map 17% reduce 0%
  13/11/19 13:42:18 INFO mapred.JobClient:  map 18% reduce 0%
  13/11/19 13:42:29 INFO mapred.JobClient:  map 19% reduce 0%
  13/11/19 13:42:36 INFO mapred.JobClient:  map 20% reduce 0%
  13/11/19 13:42:42 INFO mapred.JobClient:  map 21% reduce 0%
  13/11/19 13:42:50 INFO mapred.JobClient:  map 22% reduce 0%
  13/11/19 13:42:57 INFO mapred.JobClient:  map 23% reduce 0%
  13/11/19 13:43:07 INFO mapred.JobClient:  map 24% reduce 0%
  13/11/19 13:43:17 INFO mapred.JobClient:  map 25% reduce 0%
  13/11/19 13:43:27 INFO mapred.JobClient:  map 26% reduce 0%
  13/11/19 13:43:37 INFO mapred.JobClient:  map 27% reduce 0%
  13/11/19 13:43:47 INFO mapred.JobClient:  map 28% reduce 0%
  13/11/19 13:43:54 INFO mapred.JobClient:  map 29% reduce 0%
  13/11/19 13:44:03 INFO mapred.JobClient:  map 30% reduce 0%
  13/11/19 13:44:12 INFO mapred.JobClient:  map 31% reduce 0%
  13/11/19 13:44:18 INFO mapred.JobClient:  map 32% reduce 0%
  13/11/19 13:44:28 INFO mapred.JobClient:  map 33% reduce 0%
  13/11/19 13:44:38 INFO mapred.JobClient:  map 34% reduce 0%
  13/11/19 13:44:48 INFO mapred.JobClient:  map 35% reduce 0%
  13/11/19 13:44:54 INFO mapred.JobClient:  map 36% reduce 0%
  13/11/19 13:45:02 INFO mapred.JobClient:  map 37% reduce 0%
  13/11/19 13:45:16 INFO mapred.JobClient:  map 38% reduce 0%
  13/11/19 13:45:21 INFO mapred.JobClient:  map 39% reduce 0%
  13/11/19 13:45:33 INFO mapred.JobClient:  map 40% reduce 0%
  13/11/19 13:45:39 INFO mapred.JobClient:  map 41% reduce 0%
  13/11/19 13:45:50 INFO mapred.JobClient:  map 42% reduce 0%
  13/11/19 13:45:58 INFO mapred.JobClient:  map 43% reduce 0%
  13/11/19 13:46:06 INFO mapred.JobClient:  map 44% reduce 0%
  13/11/19 13:46:17 INFO mapred.JobClient:  map 45% reduce 0%
  13/11/19 13:46:23 INFO mapred.JobClient:  map 46% reduce 0%
  13/11/19 13:46:32 INFO mapred.JobClient:  map 47% reduce 0%
  13/11/19 13:46:39 INFO mapred.JobClient:  map 48% reduce 0%
  13/11/19 13:46:44 INFO mapred.JobClient:  map 49% reduce 0%
  13/11/19 13:46:54 INFO mapred.JobClient:  map 50% reduce 0%
  13/11/19 13:47:01 INFO mapred.JobClient:  map 51% reduce 0%
  13/11/19 13:47:09 INFO mapred.JobClient:  map 52% reduce 0%
  13/11/19 13:47:20 INFO mapred.JobClient:  map 53% reduce 0%
  13/11/19 13:47:26 INFO mapred.JobClient:  map 54% reduce 0%
  13/11/19 13:47:36 INFO mapred.JobClient:  map 55% reduce 0%
  13/11/19 13:47:47 INFO mapred.JobClient:  map 56% reduce 0%
  13/11/19 13:47:59 INFO mapred.JobClient:  map 57% reduce 0%
  13/11/19 13:48:02 INFO mapred.JobClient:  map 58% reduce 0%
  13/11/19 13:48:14 INFO mapred.JobClient:  map 59% reduce 0%
  13/11/19 13:48:25 INFO mapred.JobClient:  map 60% reduce 0%
  13/11/19 13:48:37 INFO mapred.JobClient:  map 61% reduce 0%
  13/11/19 13:48:48 INFO mapred.JobClient:  map 62% reduce 0%
  13/11/19 13:48:56 INFO mapred.JobClient:  map 63% reduce 0%
  13/11/19 13:49:07 INFO mapred.JobClient:  map 64% reduce 0%
  13/11/19 13:49:17 INFO mapred.JobClient:  map 65% reduce 0%
  13/11/19 13:49:27 INFO mapred.JobClient:  map 66% reduce 0%
  13/11/19 13:49:36 INFO mapred.JobClient:  map 67% reduce 0%
  13/11/19 13:49:45 INFO mapred.JobClient:  map 68% reduce 0%
  13/11/19 13:49:55 INFO mapred.JobClient:  map 69% reduce 0%
  13/11/19 13:50:03 INFO mapred.JobClient:  map 70% reduce 0%
  13/11/19 13:50:17 INFO mapred.JobClient:  map 71% reduce 0%
  13/11/19 13:50:26 INFO mapred.JobClient:  map 72% reduce 0%
  13/11/19 13:50:35 INFO mapred.JobClient:  map 73% reduce 0%
  13/11/19 13:50:46 INFO mapred.JobClient:  map 74% reduce 0%
  13/11/19 13:50:56 INFO mapred.JobClient:  map 75% reduce 0%
  13/11/19 13:51:04 INFO mapred.JobClient:  map 76% reduce 0%
  13/11/19 13:51:13 INFO mapred.JobClient:  map 77% reduce 0%
  13/11/19 13:51:19 INFO mapred.JobClient:  map 78% reduce 0%
  13/11/19 13:51:33 INFO mapred.JobClient:  map 79% reduce 0%
  13/11/19 13:51:41 INFO mapred.JobClient:  map 80% reduce 0%
  13/11/19 13:51:51 INFO mapred.JobClient:  map 81% reduce 0%
  13/11/19 13:52:02 INFO mapred.JobClient:  map 82% reduce 0%
  13/11/19 13:52:07 INFO mapred.JobClient:  map 83% reduce 0%
  13/11/19 13:52:18 INFO mapred.JobClient:  map 84% reduce 0%
  13/11/19 13:52:30 INFO mapred.JobClient:  map 85% reduce 0%
  13/11/19 13:52:41 INFO mapred.JobClient:  map 86% reduce 0%
  13/11/19 13:52:54 INFO mapred.JobClient:  map 87% reduce 0%
  13/11/19 13:53:06 INFO mapred.JobClient:  map 88% reduce 0%
  13/11/19 13:53:22 INFO mapred.JobClient:  map 89% reduce 0%
  13/11/19 13:53:32 INFO mapred.JobClient:  map 90% reduce 0%
  13/11/19 13:53:37 INFO mapred.JobClient:  map 91% reduce 0%
  13/11/19 13:53:54 INFO mapred.JobClient:  map 92% reduce 0%
  13/11/19 13:54:09 INFO mapred.JobClient:  map 93% reduce 0%
  13/11/19 13:54:25 INFO mapred.JobClient:  map 94% reduce 0%
  13/11/19 13:54:34 INFO mapred.JobClient:  map 95% reduce 0%
  13/11/19 13:54:49 INFO mapred.JobClient:  map 96% reduce 0%
  13/11/19 13:55:12 INFO mapred.JobClient:  map 97% reduce 0%
  13/11/19 13:55:28 INFO mapred.JobClient:  map 98% reduce 0%
  13/11/19 13:56:00 INFO mapred.JobClient:  map 99% reduce 0%
  13/11/19 13:56:58 INFO mapred.JobClient:  map 100% reduce 0%
  13/11/19 14:19:20 INFO mapred.JobClient:  map 100% reduce 1%
  13/11/19 14:23:39 INFO mapred.JobClient:  map 100% reduce 2%
  13/11/19 14:25:37 INFO mapred.JobClient:  map 100% reduce 3%
  13/11/19 14:31:12 INFO mapred.JobClient:  map 100% reduce 4%
  13/11/19 14:34:26 INFO mapred.JobClient:  map 100% reduce 5%
  13/11/19 14:35:58 INFO mapred.JobClient:  map 89% reduce 5%
  13/11/19 14:46:54 INFO mapred.JobClient:  map 79% reduce 5%
  13/11/19 14:46:55 INFO mapred.JobClient:  map 79% reduce 6%
  13/11/19 14:53:09 INFO mapred.JobClient:  map 79% reduce 7%
  13/11/19 14:56:08 INFO mapred.JobClient:  map 79% reduce 8%
  13/11/19 14:56:50 INFO mapred.JobClient: Task Id : attempt_201310311057_0040_m_000006_0, Status : FAILED
  Task attempt_201310311057_0040_m_000006_0 failed to report status for 1225 seconds. Killing!
  Task attempt_201310311057_0040_m_000006_0 failed to report status for 1249 seconds. Killing!
  13/11/19 14:57:59 WARN mapred.JobClient: Error reading task outputRead timed out
  13/11/19 14:59:00 WARN mapred.JobClient: Error reading task outputRead timed out
  13/11/19 14:59:01 INFO mapred.JobClient:  map 70% reduce 8%
  13/11/19 14:59:20 INFO mapred.JobClient:  map 71% reduce 8%
  13/11/19 15:00:50 INFO mapred.JobClient:  map 71% reduce 9%
  13/11/19 15:01:41 INFO mapred.JobClient:  map 71% reduce 10%
  13/11/19 15:01:54 INFO mapred.JobClient:  map 72% reduce 10%
  13/11/19 15:02:25 INFO mapred.JobClient:  map 73% reduce 10%
  13/11/19 15:02:34 INFO mapred.JobClient: Task Id : attempt_201310311057_0040_m_000005_0, Status : FAILED
  Task attempt_201310311057_0040_m_000005_0 failed to report status for 1212 seconds. Killing!
  13/11/19 15:03:16 INFO mapred.JobClient:  map 74% reduce 10%
  13/11/19 15:04:08 INFO mapred.JobClient:  map 75% reduce 10%
  13/11/19 15:04:48 INFO mapred.JobClient:  map 76% reduce 10%
  13/11/19 15:06:19 INFO mapred.JobClient:  map 77% reduce 10%
  13/11/19 15:07:35 INFO mapred.JobClient:  map 77% reduce 11%
  13/11/19 15:07:46 INFO mapred.JobClient:  map 78% reduce 11%
  13/11/19 15:09:46 INFO mapred.JobClient:  map 79% reduce 11%
  13/11/19 15:10:11 INFO mapred.JobClient:  map 79% reduce 12%
  13/11/19 15:12:00 INFO mapred.JobClient:  map 80% reduce 12%
  13/11/19 15:12:56 INFO mapred.JobClient:  map 81% reduce 12%
  13/11/19 15:13:46 INFO mapred.JobClient:  map 82% reduce 12%
  13/11/19 15:14:37 INFO mapred.JobClient:  map 83% reduce 12%
  13/11/19 15:15:36 INFO mapred.JobClient:  map 84% reduce 12%
  13/11/19 15:16:41 INFO mapred.JobClient:  map 85% reduce 12%
  13/11/19 15:17:44 INFO mapred.JobClient:  map 86% reduce 12%
  13/11/19 15:18:45 INFO mapred.JobClient:  map 87% reduce 12%
  13/11/19 15:20:22 INFO mapred.JobClient:  map 88% reduce 12%
  13/11/19 15:22:41 INFO mapred.JobClient:  map 89% reduce 12%
  13/11/19 15:23:57 INFO mapred.JobClient: Task Id : attempt_201310311057_0040_m_000004_0, Status : FAILED
  Task attempt_201310311057_0040_m_000004_0 failed to report status for 1378 seconds. Killing!
  Task attempt_201310311057_0040_m_000004_0 failed to report status for 1292 seconds. Killing!
  13/11/19 15:24:00 INFO mapred.JobClient:  map 89% reduce 13%
  13/11/19 15:25:08 INFO mapred.JobClient:  map 79% reduce 13%
  13/11/19 15:26:44 INFO mapred.JobClient:  map 69% reduce 13%
  13/11/19 15:28:15 INFO mapred.JobClient:  map 70% reduce 13%
  13/11/19 15:28:40 INFO mapred.JobClient:  map 71% reduce 13%
  13/11/19 15:29:06 INFO mapred.JobClient:  map 71% reduce 12%
  13/11/19 15:29:31 INFO mapred.JobClient:  map 72% reduce 12%
  13/11/19 15:30:13 INFO mapred.JobClient:  map 73% reduce 12%
  13/11/19 15:30:36 INFO mapred.JobClient: Task Id : attempt_201310311057_0040_m_000003_0, Status : FAILED
  Task attempt_201310311057_0040_m_000003_0 failed to report status for 1203 seconds. Killing!
  13/11/19 15:30:36 INFO mapred.JobClient: Task Id : attempt_201310311057_0040_m_000002_0, Status : FAILED
  Task attempt_201310311057_0040_m_000002_0 failed to report status for 1200 seconds. Killing!
  13/11/19 15:30:36 INFO mapred.JobClient: Task Id : attempt_201310311057_0040_r_000006_0, Status : FAILED
  Task attempt_201310311057_0040_r_000006_0 failed to report status for 1202 seconds. Killing!
  13/11/19 15:31:14 INFO mapred.JobClient:  map 74% reduce 12%
  13/11/19 15:31:39 INFO mapred.JobClient:  map 75% reduce 12%
  13/11/19 15:32:29 INFO mapred.JobClient:  map 76% reduce 12%
  13/11/19 15:33:43 INFO mapred.JobClient:  map 77% reduce 12%
  13/11/19 15:34:24 INFO mapred.JobClient:  map 77% reduce 13%
  13/11/19 15:34:42 INFO mapred.JobClient:  map 78% reduce 13%
  13/11/19 15:35:02 INFO mapred.JobClient:  map 78% reduce 14%
  13/11/19 15:35:34 INFO mapred.JobClient:  map 79% reduce 14%
  13/11/19 15:36:29 INFO mapred.JobClient:  map 80% reduce 14%
  13/11/19 15:36:51 INFO mapred.JobClient:  map 80% reduce 15%
  13/11/19 15:37:12 INFO mapred.JobClient:  map 81% reduce 15%
  13/11/19 15:37:46 INFO mapred.JobClient:  map 82% reduce 15%
  13/11/19 15:38:12 INFO mapred.JobClient:  map 83% reduce 15%
  13/11/19 15:38:39 INFO mapred.JobClient:  map 84% reduce 15%
  13/11/19 15:39:18 INFO mapred.JobClient:  map 85% reduce 15%
  13/11/19 15:39:50 INFO mapred.JobClient:  map 86% reduce 15%
  13/11/19 15:40:16 INFO mapred.JobClient:  map 87% reduce 15%
  13/11/19 15:40:52 INFO mapred.JobClient:  map 88% reduce 15%
  13/11/19 15:41:18 INFO mapred.JobClient:  map 89% reduce 15%
  13/11/19 15:41:48 INFO mapred.JobClient:  map 90% reduce 15%
  13/11/19 15:42:47 INFO mapred.JobClient:  map 91% reduce 15%
  13/11/19 15:43:58 INFO mapred.JobClient:  map 92% reduce 15%
  13/11/19 15:45:36 INFO mapred.JobClient:  map 93% reduce 15%
  13/11/19 15:46:29 INFO mapred.JobClient:  map 93% reduce 16%
  13/11/19 15:46:53 INFO mapred.JobClient:  map 94% reduce 16%
  13/11/19 15:48:25 INFO mapred.JobClient:  map 94% reduce 17%
  13/11/19 15:48:56 INFO mapred.JobClient:  map 95% reduce 17%
  13/11/19 15:50:37 INFO mapred.JobClient:  map 96% reduce 17%
  13/11/19 15:51:46 INFO mapred.JobClient:  map 96% reduce 18%
  13/11/19 15:52:15 INFO mapred.JobClient:  map 97% reduce 18%
  13/11/19 15:53:08 INFO mapred.JobClient:  map 97% reduce 19%
  13/11/19 15:56:03 INFO mapred.JobClient:  map 97% reduce 20%
  13/11/19 15:56:54 INFO mapred.JobClient:  map 98% reduce 20%
  13/11/19 15:57:10 INFO mapred.JobClient:  map 98% reduce 21%
  13/11/19 15:59:26 INFO mapred.JobClient:  map 99% reduce 21%
  13/11/19 16:02:58 INFO mapred.JobClient:  map 100% reduce 21%
  13/11/19 16:03:57 INFO mapred.JobClient:  map 100% reduce 22%
  13/11/19 16:30:35 INFO mapred.JobClient:  map 100% reduce 23%
  13/11/19 16:35:00 INFO mapred.JobClient:  map 100% reduce 24%
  13/11/19 16:40:35 INFO mapred.JobClient:  map 100% reduce 25%
  13/11/19 16:40:38 INFO mapred.JobClient:  map 100% reduce 26%
  13/11/19 16:44:38 INFO mapred.JobClient:  map 100% reduce 27%
  13/11/19 16:49:08 INFO mapred.JobClient:  map 100% reduce 28%
  13/11/19 16:49:30 INFO mapred.JobClient:  map 100% reduce 29%
  13/11/19 16:52:25 INFO mapred.JobClient:  map 100% reduce 33%
  13/11/19 16:53:54 INFO mapred.JobClient:  map 100% reduce 38%
  13/11/19 16:54:10 INFO mapred.JobClient:  map 100% reduce 42%
  13/11/19 16:55:21 INFO mapred.JobClient:  map 100% reduce 43%
  13/11/19 16:55:36 INFO mapred.JobClient:  map 100% reduce 47%
  13/11/19 16:55:39 INFO mapred.JobClient:  map 100% reduce 56%
  13/11/19 16:56:40 INFO mapred.JobClient:  map 100% reduce 57%
  13/11/19 16:58:04 INFO mapred.JobClient:  map 100% reduce 58%
  13/11/19 17:01:25 INFO mapred.JobClient:  map 100% reduce 59%
  13/11/19 17:04:47 INFO mapred.JobClient:  map 100% reduce 64%
  13/11/19 17:05:01 INFO mapred.JobClient:  map 100% reduce 69%
  13/11/19 17:07:39 INFO mapred.JobClient:  map 100% reduce 70%
  13/11/19 17:10:32 INFO mapred.JobClient:  map 100% reduce 71%
  13/11/19 17:13:21 INFO mapred.JobClient:  map 100% reduce 72%
  13/11/19 17:16:08 INFO mapred.JobClient:  map 100% reduce 73%
  13/11/19 17:19:03 INFO mapred.JobClient:  map 100% reduce 74%
  13/11/19 17:21:55 INFO mapred.JobClient:  map 100% reduce 75%
  13/11/19 17:24:46 INFO mapred.JobClient:  map 100% reduce 76%
  13/11/19 17:27:35 INFO mapred.JobClient:  map 100% reduce 77%
  13/11/19 17:30:24 INFO mapred.JobClient:  map 100% reduce 78%
  13/11/19 17:33:14 INFO mapred.JobClient:  map 100% reduce 79%
  13/11/19 17:36:07 INFO mapred.JobClient:  map 100% reduce 80%
  13/11/19 17:39:00 INFO mapred.JobClient:  map 100% reduce 81%
  13/11/19 17:41:51 INFO mapred.JobClient:  map 100% reduce 82%
  13/11/19 17:44:39 INFO mapred.JobClient:  map 100% reduce 83%
  13/11/19 17:47:27 INFO mapred.JobClient:  map 100% reduce 84%
  13/11/19 17:50:22 INFO mapred.JobClient:  map 100% reduce 85%
  13/11/19 17:53:09 INFO mapred.JobClient:  map 100% reduce 86%
  13/11/19 17:55:54 INFO mapred.JobClient:  map 100% reduce 87%
  13/11/19 17:58:44 INFO mapred.JobClient:  map 100% reduce 88%
  13/11/19 18:01:35 INFO mapred.JobClient:  map 100% reduce 89%
  13/11/19 18:04:21 INFO mapred.JobClient:  map 100% reduce 90%
  13/11/19 18:07:16 INFO mapred.JobClient:  map 100% reduce 91%
  13/11/19 18:10:08 INFO mapred.JobClient:  map 100% reduce 92%
  13/11/19 18:12:55 INFO mapred.JobClient:  map 100% reduce 93%
  13/11/19 18:15:51 INFO mapred.JobClient:  map 100% reduce 94%
  13/11/19 18:18:45 INFO mapred.JobClient:  map 100% reduce 95%
  13/11/19 18:21:36 INFO mapred.JobClient:  map 100% reduce 96%
  13/11/19 18:24:25 INFO mapred.JobClient:  map 100% reduce 97%
  13/11/19 18:27:42 INFO mapred.JobClient:  map 100% reduce 98%
  13/11/19 18:31:25 INFO mapred.JobClient:  map 100% reduce 99%
  13/11/19 18:41:13 INFO mapred.JobClient:  map 100% reduce 100%
  </code></pre>
  
  <p>During this time (from map 100% reduce 0% to map 100% reduce 5%),  I observed that only 5 map tasks are completed (out of a total of 10), then the other 5 fail because of timeout. Then they re ran. I know this can be fixed by increasing the timeout, this is not the point of my question.</p>
  
  <p>I know that in between Map and Reduce, what happens is that the data is being commited, shuffled and sort. First question. Is it normal having to wait so long between a map phase and a reduce phase with this data size? It doesn't feel right.</p>
  
  <p>My reducer is kinda computationally heavy, so I changed it to an identity reducer. But this didn't seem to help much. Which makes me think that the problem is either in my mapper, or in the shuffling/sorting. So here's my mapper.</p>
  
  <pre><code>  public static class CliquesMapper extends
        Mapper&lt;YearTermKey, SetWritable, YearTermKey, MapWritable&gt; {
  
      private YearTermKey outputKEY=new YearTermKey();
  
  
      public void map(YearTermKey key, SetWritable value, Context context)
          throws IOException, InterruptedException {
  
          Set&lt;Writable&gt; neighbors=value.keySet();
          int listSize=neighbors.size();
          if(listSize!=1){
              for(Writable keyTerm:neighbors){
                  IntWritable KEYTerm=(IntWritable) keyTerm;
                  outputKEY.set(new Text(key.getYear()), KEYTerm);
                  MapWritable outputVALUE=new MapWritable();
                  outputVALUE.put(key.getTerm(), value);                  
                  context.write(outputKEY, outputVALUE);                                
              }
          }else{
              IntWritable finalTerm=new IntWritable();
              for(Writable t:neighbors){
                  finalTerm.set(((IntWritable) t).get());
              }
              outputKEY.set(key.getYear(), finalTerm);
              NullWritable nw=NullWritable.get();
              MapWritable outputVALUE=new MapWritable();
              outputVALUE.put(key.getTerm(), nw);
  
              context.write(outputKEY,outputVALUE);
  
          }             
      }
    }
  </code></pre>
  
  <p>Second question. Is it possible that they the key-value pairs that i am emmiting from the mapper are causing this delay? Otherwise, why is this happening?</p>
  
  <p>In any case, after all the 10 map tasks are completed (around map 100%, reduce 33%), the reducer takes nearly 2 hours to finish. How can this be possible given that it is an identity reducer?</p>