看到了吗https://community.cloudera.com/t5/support-questions/hive-multiple-small-files/td-p/204038

set hive.merge.mapfiles=true;     -- Merge small files at the end of a map-only job.
set hive.merge.mapredfiles=true;  -- Merge small files at the end of a map-reduce job.

set hive.merge.size.per.task=???; -- Size (bytes) of merged files at the end of the job.

set hive.merge.smallfiles.avgsize=??? -- File size (bytes) threshold
-- When the average output file size of a job is less than this number, 
-- Hive will start an additional map-reduce job to merge the output files 
-- into bigger files. This is only done for map-only jobs if hive.merge.mapfiles 
-- is true, and for map-reduce jobs if hive.merge.mapredfiles is true.

限制输出文件的数量意味着您要限制减速器的数量。你可以借助 mapred.reduce.tasks 属性。例子：

hive>  set mapred.reduce.tasks = 5;

但它可能会影响查询的性能。或者，你可以使用 getmerge 完成查询后，从hdfsshell发出命令。此命令将源目录和目标文件作为输入，并将src中的文件连接到目标本地文件中。
用法：

bin/hadoop fs -getmerge <src> <localdst>

hth公司