You understanding is correct. I would define it as following: If you do not need sorting of map results – you set 0 reduced,and the job is called map only. If you need to sort the mapping results, but do not need any aggregation – you choose identity reducer. And to complete the picture we … Read more
Using Hive in HDInsight, I set the following properties before I create my external table in the Hive query and it works for me. SET hive.mapred.supports.subdirectories=TRUE; SET mapred.input.dir.recursive=TRUE;
First of all, open up your job tracker and look at the number of free reducer slots and other running jobs – is there another job running which is consuming all the free reducer slots when then become available. Once you’ve proved to yourself that there are some free reducer slots available to run a … Read more
Here is the current state of functionality for Map/Reduce in MongoDB 1) Most of the performance limitations for Map/Reduce still remain in MongoDB version 2.2. The Map/Reduce engine still requires that every record get converted from BSON to JSON, the actual calculations are performed using the embedded JavaScript engine (which is slow), and there still … Read more
That’s not the real error, here’s how to find it: Go to the hadoop jobtracker web-dashboard, find the hive mapreduce jobs that failed and look at the logs of the failed tasks. That will show you the real error. The console output errors are useless, largely beause it doesn’t have a view of the individual … Read more
Try: sed -n ‘$=’ filename Also cat is unnecessary: wc -l filename is enough in your present way.
The exception is a bit misleading; there’s no real relative path being parsed, the issue here is that Hadoop “Path” doesn’t support ‘:’ in filenames. In your case, “rsrc:hbase-common-0.98.1-hadoop2.jar” is being interpreted as “rsrc” being the “scheme”, whereas I suspect you really intended to add the resource file:///path/to/your/jarfile/rsrc:hbase-common-0.98.1-hadoop2.jar”. Here’s an old JIRA discussing the illegal … Read more
How Many Reduces? ( From official documentation) The right number of reduces seems to be 0.95 or 1.75 multiplied by (no. of nodes) * (no. of maximum containers per node). With 0.95 all of the reduces can launch immediately and start transferring map outputs as the maps finish. With 1.75 the faster nodes will finish … Read more
The answer by @user1668782 is a great explanation for the question and I’ll try to give a graphical depiction of it. Assume we have a file of 400MB with consists of 4 records(e.g : csv file of 400MB and it has 4 rows, 100MB each) If the HDFS Block Size is configured as 128MB, then … Read more