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
In order to keep everything on the grid use hadoop streaming with a single reducer and cat as the mapper and reducer (basically a noop) – add compression using MR flags. hadoop jar \ $HADOOP_PREFIX/share/hadoop/tools/lib/hadoop-streaming.jar \<br> -Dmapred.reduce.tasks=1 \ -Dmapred.job.queue.name=$QUEUE \ -input “$INPUT” \ -output “$OUTPUT” \ -mapper cat \ -reducer cat If you want compression … Read more
In short, for your questions: Does CLUSTER BY guarantee a global order? No. DISTRIBUTE BY puts the same keys into same reducers but what about the adjacent keys? Depends on the hash function, which depends on your query. related question: How does the built-in Apache Hive hash function work and where can I find that … Read more
Check your core-site.xml : <property> <name>fs.default.name</name> <value>hdfs://host:port</value> </property> This port can be 9000 or 8020. Make sure that you are using the same port in your code or command
Typically, you can quantify how well an algorithm will scale by using big-O notation to analyze its growth rate. When you say that your algorithm works by “brute force,” it’s unclear to what extent it will scale. If your “brute force” solution works by listing all possible subsets or combinations of a set of data, … Read more
The split size is calculated by the formula:- max(mapred.min.split.size, min(mapred.max.split.size, dfs.block.size)) In your case it will be:- split size=max(128,min(Long.MAX_VALUE(default),64)) So above inference:- each map will process 2 hdfs blocks(assuming each block 64MB): True There will be a new division of my input file (previously included HDFS) to occupy blocks in HDFS 128M: False but making … 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;
It is absolutely possible without doing anything extra. Hadoop provides us the facility to read/write binary files. So, practically anything which can be converted into bytes can be stored into HDFS(images, videos etc). To do that Hadoop provides something called as SequenceFiles. SequenceFile is a flat file consisting of binary key/value pairs. The SequenceFile provides … Read more
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