MapReduce

问题 I am using Ubuntu 20.10 on Virtual Box and Hadoop version 3.2.1 (if you need any more info comment me). My output at this moment gives me this : Aaron Wells Peirsol ,M,17,United States,Swimming,2000 Summer,0,1,0 Aaron Wells Peirsol ,M,21,United States,Swimming,2004 Summer,1,0,0 Aaron Wells Peirsol ,M,25,United States,Swimming,2008 Summer,0,1,0 Aaron Wells Peirsol ,M,25,United States,Swimming,2008 Summer,1,0,0 For the above output I would like to be able to sum all of his medals (the three

问题 There is Hive 2.1.1 over MR, table test_table stored as sequencefile and the following ad-hoc query: select t.* from test_table t where t.test_column = 100 Although this query can be executed without starting MR (fetch task), sometimes it takes longer to scan HDFS files rather than triggering a single map job. When I want to enforce MR execution, I make the query more complex: e.g., using distinct . The significant drawbacks of this approach are: Query results may differ from the original

问题 Following are my two collections users:{ _id: "", email: "test@gmail.com", department: "hr" } details:{ _id: "", email: "abc@gmail.com" some_data:[ {user_email: "test@gmail.com", ....}, {user_email: "test1@gmail.com", ....}, {user_email: "test@gmail.com", ....}, ] } What I require is an output saying top 3 departments in the details based on email. Example: If I query for email: abc@gmail.com, I must get [ {department: "hr", count: 4}, {department: "finance", count: 3}, {department: "IT",

问题 Following are my two collections users:{ _id: "", email: "test@gmail.com", department: "hr" } details:{ _id: "", email: "abc@gmail.com" some_data:[ {user_email: "test@gmail.com", ....}, {user_email: "test1@gmail.com", ....}, {user_email: "test@gmail.com", ....}, ] } What I require is an output saying top 3 departments in the details based on email. Example: If I query for email: abc@gmail.com, I must get [ {department: "hr", count: 4}, {department: "finance", count: 3}, {department: "IT",

问题 In Hive I ofter do queries like: select columnA, sum(columnB) from ... group by ... I read some mapreduce example and one reducer can only produce one key. It seems the number of reducers completely depends on number of keys in columnA. Therefore, why could hive set number of reducers manully? If there are 10 different values in columnA and I set number of reducers to 2 , what will happen? Each reducers will be reused 5 times? If there are 10 different values in columnA and I set number of

问题 In Hive I ofter do queries like: select columnA, sum(columnB) from ... group by ... I read some mapreduce example and one reducer can only produce one key. It seems the number of reducers completely depends on number of keys in columnA. Therefore, why could hive set number of reducers manully? If there are 10 different values in columnA and I set number of reducers to 2 , what will happen? Each reducers will be reused 5 times? If there are 10 different values in columnA and I set number of

问题 I tried this command in command prompt (run as administrator): hadoop jar C:\Users\tejashri\Desktop\Hadoopproject\WordCount.jar WordcountDemo.WordCount /work /out but i got this error message: my application got stopped. 2020-04-04 23:53:27,918 INFO client.RMProxy: Connecting to ResourceManager at /0.0.0.0:8032 2020-04-04 23:53:28,881 WARN mapreduce.JobResourceUploader: Hadoop command-line option parsing not performed. Implement the Tool interface and execute your application with ToolRunner

问题 I have an AVRO file(created by JAVA) and seems like it is some kind of zipped file for hadoop/mapreduce, i want to 'unzip' (deserialize) it to a flat file. Per record per row. I learned that there is an AVRO package for python, and I installed it correctly. And run the example to read the AVRO file. However, it came up with the errors below and I am wondering what is going on reading the simplest example? Can anyone help me interpret the errors bellow. >>> reader = DataFileReader(open("/tmp

问题 I'm new to RavenDB, and am loving it so far. I have one remaining index to create for my project. The Problem I have thousands of responses to surveys (i.e. " Submissions "), and each submission has an array of answers to specific questions (i.e. " Answers "), and each answer has an array of options that were selected (i.e. " Values "). Here is what a single Submission basically looks like: { "SurveyId": 1, "LocationId": 1, "Answers": [ { "QuestionId": 1, "Values": [2,8,32], "Comment": null }

问题 I'm new to RavenDB, and am loving it so far. I have one remaining index to create for my project. The Problem I have thousands of responses to surveys (i.e. " Submissions "), and each submission has an array of answers to specific questions (i.e. " Answers "), and each answer has an array of options that were selected (i.e. " Values "). Here is what a single Submission basically looks like: { "SurveyId": 1, "LocationId": 1, "Answers": [ { "QuestionId": 1, "Values": [2,8,32], "Comment": null }