Hive 关于merge的几个参数
hive.merge.mapfiles(defaulttrue)：这个参数是用来控制是否merge MAP-ONLY型Job的文件输出（如果在Hive里设置了支持DP的话，并且
分析一下Hive 关于merge的三个容易混淆的参数：
hive.mergejob.maponly
hive.merge.mapfiles
hive.merge.mapredfiles
这三个参数是merge以哪种方式的输出文件，以及以哪种方merge.听起来是不是很绕J
hive.merge.mapfiles(defaulttrue)：这个参数是用来控制是否merge MAP-ONLY型Job的文件输出（如果在Hive里设置了支持DP的话，并且涉及到含有DP列的表，如果Hadoop不支持CombineInputFormat，即版本pre-0.20的话那么这个参数和下个参数是不生效的，即都是false）
hive.merge.mapredfiles(defaultfalse)：这个参数是用来控制merge MAP-REDUCE型Job的文件输出
hive.mergejob.maponly(defaulttrue)：这个参数是用来控制是以MAP-ONLY的形式来进行merge（这里有个前提条件就是需要Hadoop支持CombineInputFormat，，0.20之前的即使设置了这个参数true也不会生效）或者以MAP-REDUCE的形式来进行merge.不过关于这个参数还有一个未修复的Bug（https://issues.apache.org/jira/browse/HIVE-2869）因此默认值是true
Hive 的详细介绍：请点这里
Hive 的下载地址：请点这里
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