Fetch抓取是指：Hive在某些情況下的查詢可以不用走MapReduce程序，如全表查詢、字段查詢、limit查詢。 ```sql hive (default)> select * from emp; hive (default)> select ename from emp; hive (default)> select ename from emp limit 5; ``` 像上面的三種查詢，Hive可以簡單地讀取到employee對應的hdfs存儲目錄下的文件，將結果輸出。 <br/> **開啟Fetch抓取：** *`{hive_home}/conf/hive-site.xml`* ```xml <property> <name>hive.fetch.task.conversion</name> <!-- 默認就是more，開啟--> <value>more</value> <description> Expects one of [none, minimal, more]. Some select queries can be converted to single FETCH task minimizing latency. Currently the query should be single sourced not having any subquery and should not have any aggregations or distincts (which incurs RS), lateral views and joins. 0. none : disable hive.fetch.task.conversion 1. minimal : SELECT STAR, FILTER on partition columns, LIMIT only // more: 該屬性修改為 more 以后，在全局查找、字段查找、limit 查找等都不走 mapreduce 2. more : SELECT, FILTER, LIMIT only (support TABLESAMPLE andvirtual columns) </description> </property> ```