hadoop-partitioning

问题 Does the Hadoop split the data based on the number of mappers set in the program? That is, having a data set of size 500MB, if the number of mappers is 200 (assuming that the Hadoop cluster allows 200 mappers simultaneously), is each mapper given 2.5 MB of data? Besides,do all the mappers run simultaneously or some of them might get run in serial? 回答1: I just ran a sample MR program based on your question and here is my finding Input: a file smaller that block size. Case 1: Number of mapper

问题 I have following record set to process like 1000, 1001, 1002 to 1999, 2000, 2001, 2002 to 2999, 3000, 3001, 3002 to 3999 And I want to process the following record set using HIVE in such a way so that reducer-1 will process data 1000 to 1999 and reducer-2 will process data 2000 to 2999 and reducer-3 will process data 3000 to 3999.Please help me to solve above problem. 回答1: Use DISTRIBUTE BY , mappers output is being grouped according to the distribute by clause to be transferred to reducers

问题 I am exploring windowing functions in Hive and I am able to understand the functionalities of all the UDFs. Although, I am not able to understand the partition by and order by that we use with the other functions. Following is the structure that is very similar to the query which I am planning to build. SELECT a, RANK() OVER(partition by b order by c) as d from xyz; Just trying to understand the background process involved for both keywords. Appreciate the help :) 回答1: RANK() analytic

问题 Using hadoop multinode setup (1 mater , 1 salve) After starting up start-mapred.sh on master , i found below error in TT logs (Slave an) org.apache.hadoop.mapred.TaskTracker: Failed to get system directory can some one help me to know what can be done to avoid this error I am using Hadoop 1.2.0 jetty-6.1.26 java version "1.6.0_23" mapred-site.xml file <configuration> <property> <name>mapred.job.tracker</name> <value>master:54311</value> <description>The host and port that the MapReduce job

问题 Using hadoop multinode setup (1 mater , 1 salve) After starting up start-mapred.sh on master , i found below error in TT logs (Slave an) org.apache.hadoop.mapred.TaskTracker: Failed to get system directory can some one help me to know what can be done to avoid this error I am using Hadoop 1.2.0 jetty-6.1.26 java version "1.6.0_23" mapred-site.xml file <configuration> <property> <name>mapred.job.tracker</name> <value>master:54311</value> <description>The host and port that the MapReduce job

问题 I have a custom partitioner like below: import java.util.*; import org.apache.hadoop.mapreduce.*; public static class SignaturePartitioner extends Partitioner<Text,Text> { @Override public int getPartition(Text key,Text value,int numReduceTasks) { return (key.toString().Split(' ')[0].hashCode() & Integer.MAX_VALUE) % numReduceTasks; } } I set the hadoop streaming parameter like below -file SignaturePartitioner.java \ -partitioner SignaturePartitioner \ Then I get an error: Class Not Found. Do

问题 i have an external partitioned table named employee with partition(year,month,day), everyday a new file come and seat at the particular day location call for today's date it will be at 2016/10/13. TABLE SCHEMA: create External table employee(EMPID Int,FirstName String,.....) partitioned by (year string,month string,day string) ROW FORMAT DELIMITED FIELDS TERMINATED BY ',' LINES TERMINATED BY '\n' LOCATION '/.../emp'; so everyday we need to run command which is working fine as ALTER TABLE

问题 i have an external partitioned table named employee with partition(year,month,day), everyday a new file come and seat at the particular day location call for today's date it will be at 2016/10/13. TABLE SCHEMA: create External table employee(EMPID Int,FirstName String,.....) partitioned by (year string,month string,day string) ROW FORMAT DELIMITED FIELDS TERMINATED BY ',' LINES TERMINATED BY '\n' LOCATION '/.../emp'; so everyday we need to run command which is working fine as ALTER TABLE

问题 I am trying to make a custom partitioner to allocate each unique key to a single reducer. this was after the default HashPartioner failed Alternative to the default hashpartioner provided with hadoop I keep getting the following error. It has something to do with the constructor not receiving its arguments, from what I can tell from doing some research. but in this context, with hadoop, aren't the arguments passed automatically by the framework? I cant find an error in the code 18/04/20 17:06

问题 As we know that Hadoop guarantees that the same keys which come from different mappers will be sent to the same reducer . But if two different keys have the same hash value , they definitely will go to the same reducer , so will them be sent to the same reduce method orderly ? Which part is responsible for this logic? Thanks a lot! 回答1: Q1: so will them be sent to the same reduce method orderly Ans : yes Q2: Which part is responsible for this logic Ans : shuffle sort Example : key value 1 2 1