In order to limit the maximum number of reducers: Tuning this value down increases parallelism and may improve performance. Reducers: There are two conditions for no. so if you are playing with less than 1 GB of data and you are not specifically setting the number of reducer so 1 reducer would be used . Too many reducers and you end up with lots of small files. A single reducer might work on one or more partitions. Using this property could increase or decrease the execution time of the query depending on size of the data or number of files to merge. number of reducers using the following formula and then schedules the Tez DAG. c. In the Add Property window, enter mapred.map.output.compression.codec as the key and org.apache.hadoop.io.compress.SnappyCodec as the value. max. 17) Can reducers communicate with each other? Making statements based on opinion; back them up with references or personal experience. Can you still use Commanders Strike if the only attack available to forego is an attack against an ally? This is not recommended and you should avoid using this. https://cwiki.apache.org/confluence/display/Hive/Configuration+Properties, http://hortonworks.com/blog/apache-tez-dynamic-graph-reconfiguration/, http://www.slideshare.net/t3rmin4t0r/hivetez-a-performance-deep-dive and, http://www.slideshare.net/ye.mikez/hive-tuning (Mandatory), http://www.slideshare.net/AltorosBY/altoros-practical-steps-to-improve-apache-hive-performance, http://www.slideshare.net/t3rmin4t0r/data-organization-hive-meetup, http://www.slideshare.net/InderajRajBains/using-apache-hive-with-high-performance. second table number of splitted files in hdfs --> 17 files. Cloudera WXM can assist in evaluating the benefits of query changes during performance testing. How does Hive choose the number of reducers for a job? Embedded hyperlinks in a thesis or research paper. What does 'They're at four. Master uses these information while scheduling. The parameter for this is hive.optimize.reducededuplication.min.reducer which by default is 4. Performance is BETTER with 24 reducers than with 38 reducers. A single reducer might work on one or more partitions. Where does the version of Hamapil that is different from the Gemara come from? HIVE_HOME/bin/hive -set mapred.reducer.tasks= "command". can assist in evaluating the benefits of query changes during performance testing. There is no way to do it on a per-join basis (at least not yet). 08 April 2021, [{"Product":{"code":"SSCRJT","label":"IBM Db2 Big SQL"},"Business Unit":{"code":"BU059","label":"IBM Software w\/o TPS"},"Component":"Open Source Tools","Platform":[{"code":"PF016","label":"Linux"}],"Version":"2.0.0;2.1.0;1.4.0;1.3.0","Edition":"Enterprise Edition;Basic Edition","Line of Business":{"code":"LOB10","label":"Data and AI"}}], Resolving an exceeded max jobconf size error in Hive. exec. Total MapReduce jobs = 2 Connect and share knowledge within a single location that is structured and easy to search. (By default this is set to -1, indicating Hive should use its heuristics.). Tez could try processing this data with at least two tasks because max data/task could be 1 G. Eventually, Tez could force 1000 files (splits) to be combined to two tasks, leading to slower execution times. Why doesn't this short exact sequence of sheaves split? Content Discovery initiative April 13 update: Related questions using a Review our technical responses for the 2023 Developer Survey, Setting the number of map tasks and reduce tasks, Deciding on the optimal number of reducers to be specified for fastest processing in a Hadoop map reduce program, Hadoop "Unable to load native-hadoop library for your platform" warning, Setting the Number of Reducers in a MapReduce job which is in an Oozie Workflow, Hive takes long time to launch hadoop job. But internally the ResourceManager has its own algorithm running, optimizing things on the go. Thanks for contributing an answer to Stack Overflow! Depending on the reduce stage estimates, tweak the. Not the answer you're looking for?