Whether to enable skew join optimization. The algorithm is as follows: At runtime, detect the keys with a large skew. Instead of processing those keys, store them temporarily in an HDFS directory. In a follow-up map-reduce job, process those skewed keys. The same key need not be skewed ...
9. 10. Whether to enable skew join optimization. The algorithm is as follows: At runtime, detect the keys with a large skew. Instead of processing those keys, store them temporarily in an HDFS directory. In a follow-up map-reduce job, process those skewed keys. The same key need not ...
You must make your changes in hive-site.xml instead.-->252627<!--Hive Execution Parameters-->28<property>29<name>mapred.reduce.tasks</name>30<value>-1</value>31<description>The default number of reduce tasks per job. Typically set32to a prime close to the number of available hosts. Ig...
容易发生数据倾斜。可以用MapJoin把小表全部加载到内存在map端进行join,避免reducer处理。 1、开启MapJoin参数设置 (1)设置自动选择Mapjoin (2)大表小表的阀值设置(默认25M一下认为是小表): 2、MapJo... 黑猴子的家:Hive 文件存储格式 Hive支持的存储数的格式主要有:TEXTFILE 、SEQUENCEFILE、ORC、PARQUET 1、...