当数据量比较大，我们需要更快的完成任务，多个map和reduce进程是唯一的选择。
但是如果输入文件是一个的话，map任务只能启动一个。
此时bucket table是个很好的选择，通过指定CLUSTERED的字段，将文件通过hash打散成多个小文件。
create table sunwg_test11(id int,name string)
CLUSTERED BY(id) SORTED BY(name) INTO 32 BUCKETS
ROW FORMAT DELIMITED
FIELDS TERMINATED BY ‘/t’;
执行insert前不要忘记设置
set hive.enforce.bucketing = true;
强制采用多个reduce进行输出
hive> INSERT OVERWRITE TABLE sunwg_test11 select * from test09;
Total MapReduce jobs = 1
Launching Job 1 out of 1
Number of reduce tasks determined at compile time: 32
In order to change the average load for a reducer (in bytes):
set hive.exec.reducers.bytes.per.reducer=<number>
In order to limit the maximum number of reducers:
set hive.exec.reducers.max=<number>
In order to set a constant number of reducers:
set mapred.reduce.tasks=<number>
Starting Job = job_201103070826_0018, Tracking URL =
http://hadoop00:50030/jobdetails.jsp?jobid=job_201103070826_0018
Kill Command = /home/hjl/hadoop/bin/../bin/hadoop job -Dmapred.job.tracker=hadoop00:9001 -kill job_201103070826_0018
2011-03-08 11:34:23,055 Stage-1 map = 0%, reduce = 0%
2011-03-08 11:34:27,084 Stage-1 map = 6%, reduce = 0%
2011-03-08 11:34:29,100 Stage-1 map = 13%, reduce = 0%
2011-03-08 11:34:32,124 Stage-1 map = 19%, reduce = 0%
2011-03-08 11:34:34,142 Stage-1 map = 22%, reduce = 0%
2011-03-08 11:34:35,151 Stage-1 map = 25%, reduce = 0%
2011-03-08 11:34:37,167 Stage-1 map = 28%, reduce = 0%
2011-03-08 11:34:39,182 Stage-1 map = 31%, reduce = 0%
2011-03-08 11:34:41,199 Stage-1 map = 34%, reduce = 1%
2011-03-08 11:34:42,211 Stage-1 map = 38%, reduce = 1%
2011-03-08 11:34:44,233 Stage-1 map = 41%, reduce = 1%
2011-03-08 11:34:46,250 Stage-1 map = 44%, reduce = 1%
2011-03-08 11:34:48,270 Stage-1 map = 47%, reduce = 1%
2011-03-08 11:34:49,280 Stage-1 map = 50%, reduce = 1%
2011-03-08 11:34:51,300 Stage-1 map = 53%, reduce = 1%
2011-03-08 11:34:53,316 Stage-1 map = 56%, reduce = 1%
2011-03-08 11:34:55,330 Stage-1 map = 59%, reduce = 1%
2011-03-08 11:34:56,340 Stage-1 map = 63%, reduce = 1%
2011-03-08 11:34:58,357 Stage-1 map = 66%, reduce = 1%
2011-03-08 11:35:00,378 Stage-1 map = 69%, reduce = 1%
2011-03-08 11:35:02,393 Stage-1 map = 72%, reduce = 1%
2011-03-08 11:35:04,409 Stage-1 map = 75%, reduce = 1%
2011-03-08 11:35:05,419 Stage-1 map = 78%, reduce = 1%
2011-03-08 11:35:07,435 Stage-1 map = 81%, reduce = 1%
2011-03-08 11:35:09,451 Stage-1 map = 84%, reduce = 2%
2011-03-08 11:35:12,475 Stage-1 map = 88%, reduce = 2%
2011-03-08 11:35:14,496 Stage-1 map = 91%, reduce = 2%
2011-03-08 11:35:16,513 Stage-1 map = 94%, reduce = 2%
2011-03-08 11:35:18,528 Stage-1 map = 97%, reduce = 2%
2011-03-08 11:35:20,552 Stage-1 map = 100%, reduce = 2%
2011-03-08 11:35:25,589 Stage-1 map = 100%, reduce = 6%
2011-03-08 11:35:33,645 Stage-1 map = 100%, reduce = 9%
2011-03-08 11:35:34,654 Stage-1 map = 100%, reduce = 13%
2011-03-08 11:35:39,693 Stage-1 map = 100%, reduce = 16%
2011-03-08 11:35:41,710 Stage-1 map = 100%, reduce = 19%
2011-03-08 11:35:45,740 Stage-1 map = 100%, reduce = 22%
2011-03-08 11:35:47,757 Stage-1 map = 100%, reduce = 25%
2011-03-08 11:35:52,793 Stage-1 map = 100%, reduce = 28%
2011-03-08 11:35:54,808 Stage-1 map = 100%, reduce = 31%
2011-03-08 11:35:59,844 Stage-1 map = 100%, reduce = 34%
2011-03-08 11:36:01,861 Stage-1 map = 100%, reduce = 38%
2011-03-08 11:36:05,891 Stage-1 map = 100%, reduce = 41%
2011-03-08 11:36:07,911 Stage-1 map = 100%, reduce = 44%
2011-03-08 11:36:12,947 Stage-1 map = 100%, reduce = 47%
2011-03-08 11:36:13,958 Stage-1 map = 100%, reduce = 50%
2011-03-08 11:36:19,002 Stage-1 map = 100%, reduce = 53%
2011-03-08 11:36:21,017 Stage-1 map = 100%, reduce = 56%
2011-03-08 11:36:26,053 Stage-1 map = 100%, reduce = 59%
2011-03-08 11:36:28,068 Stage-1 map = 100%, reduce = 63%
2011-03-08 11:36:33,106 Stage-1 map = 100%, reduce = 66%
2011-03-08 11:36:35,122 Stage-1 map = 100%, reduce = 69%
2011-03-08 11:36:39,152 Stage-1 map = 100%, reduce = 72%
2011-03-08 11:36:41,169 Stage-1 map = 100%, reduce = 75%
2011-03-08 11:36:46,208 Stage-1 map = 100%, reduce = 78%
2011-03-08 11:36:48,227 Stage-1 map = 100%, reduce = 81%
2011-03-08 11:36:53,262 Stage-1 map = 100%, reduce = 84%
2011-03-08 11:36:54,271 Stage-1 map = 100%, reduce = 88%
2011-03-08 11:36:59,309 Stage-1 map = 100%, reduce = 91%
2011-03-08 11:37:01,328 Stage-1 map = 100%, reduce = 94%
2011-03-08 11:37:06,365 Stage-1 map = 100%, reduce = 97%
2011-03-08 11:37:08,382 Stage-1 map = 100%, reduce = 100%
Ended Job = job_201103070826_0018
Loading data to table sunwg_test11
5 Rows loaded to sunwg_test11
OK
Time taken: 175.036 seconds
hive的sunwg_test11文件夹下面出现了32个文件，而不是一个文件
[hadoop@hadoop00 ~]$ hadoop fs -ls /hjl/sunwg_test11
Found 32 items
-rw-r–r– 3 hjl hadoop 0 2011-03-08 11:20 /hjl/sunwg_test11/attempt_201103070826_0018_r_000000_0
-rw-r–r– 3 hjl hadoop 0 2011-03-08 11:20 /hjl/sunwg_test11/attempt_201103070826_0018_r_000001_0
-rw-r–r– 3 hjl hadoop 0 2011-03-08 11:20 /hjl/sunwg_test11/attempt_201103070826_0018_r_000002_0
-rw-r–r– 3 hjl hadoop 0 2011-03-08 11:20 /hjl/sunwg_test11/attempt_201103070826_0018_r_000003_0
-rw-r–r– 3 hjl hadoop 8 2011-03-08 11:20 /hjl/sunwg_test11/attempt_201103070826_0018_r_000004_0
-rw-r–r– 3 hjl hadoop 9 2011-03-08 11:20 /hjl/sunwg_test11/attempt_201103070826_0018_r_000005_0
-rw-r–r– 3 hjl hadoop 8 2011-03-08 11:20 /hjl/sunwg_test11/attempt_201103070826_0018_r_000006_0
-rw-r–r– 3 hjl hadoop 9 2011-03-08 11:20 /hjl/sunwg_test11/attempt_201103070826_0018_r_000007_0
-rw-r–r– 3 hjl hadoop 9 2011-03-08 11:20 /hjl/sunwg_test11/attempt_201103070826_0018_r_000008_0
-rw-r–r– 3 hjl hadoop 0 2011-03-08 11:20 /hjl/sunwg_test11/attempt_201103070826_0018_r_000009_0
-rw-r–r– 3 hjl hadoop 0 2011-03-08 11:20 /hjl/sunwg_test11/attempt_201103070826_0018_r_000010_0
-rw-r–r– 3 hjl hadoop 0 2011-03-08 11:20 /hjl/sunwg_test11/attempt_201103070826_0018_r_000011_0
-rw-r–r– 3 hjl hadoop 0 2011-03-08 11:20 /hjl/sunwg_test11/attempt_201103070826_0018_r_000012_0
-rw-r–r– 3 hjl hadoop 0 2011-03-08 11:20 /hjl/sunwg_test11/attempt_201103070826_0018_r_000013_0
-rw-r–r– 3 hjl hadoop 0 2011-03-08 11:21 /hjl/sunwg_test11/attempt_201103070826_0018_r_000014_0
-rw-r–r– 3 hjl hadoop 0 2011-03-08 11:21 /hjl/sunwg_test11/attempt_201103070826_0018_r_000015_0
-rw-r–r– 3 hjl hadoop 0 2011-03-08 11:21 /hjl/sunwg_test11/attempt_201103070826_0018_r_000016_0
-rw-r–r– 3 hjl hadoop 0 2011-03-08 11:21 /hjl/sunwg_test11/attempt_201103070826_0018_r_000017_0
-rw-r–r– 3 hjl hadoop 0 2011-03-08 11:21 /hjl/sunwg_test11/attempt_201103070826_0018_r_000018_0
-rw-r–r– 3 hjl hadoop 0 2011-03-08 11:21 /hjl/sunwg_test11/attempt_201103070826_0018_r_000019_0
-rw-r–r– 3 hjl hadoop 0 2011-03-08 11:21 /hjl/sunwg_test11/attempt_201103070826_0018_r_000020_0
-rw-r–r– 3 hjl hadoop 0 2011-03-08 11:21 /hjl/sunwg_test11/attempt_201103070826_0018_r_000021_0
-rw-r–r– 3 hjl hadoop 0 2011-03-08 11:21 /hjl/sunwg_test11/attempt_201103070826_0018_r_000022_0
-rw-r–r– 3 hjl hadoop 0 2011-03-08 11:21 /hjl/sunwg_test11/attempt_201103070826_0018_r_000023_0
-rw-r–r– 3 hjl hadoop 0 2011-03-08 11:21 /hjl/sunwg_test11/attempt_201103070826_0018_r_000024_0
-rw-r–r– 3 hjl hadoop 0 2011-03-08 11:21 /hjl/sunwg_test11/attempt_201103070826_0018_r_000025_0
-rw-r–r– 3 hjl hadoop 0 2011-03-08 11:21 /hjl/sunwg_test11/attempt_201103070826_0018_r_000026_0
-rw-r–r– 3 hjl hadoop 0 2011-03-08 11:21 /hjl/sunwg_test11/attempt_201103070826_0018_r_000027_0
-rw-r–r– 3 hjl hadoop 0 2011-03-08 11:21 /hjl/sunwg_test11/attempt_201103070826_0018_r_000028_0
-rw-r–r– 3 hjl hadoop 0 2011-03-08 11:21 /hjl/sunwg_test11/attempt_201103070826_0018_r_000029_0
-rw-r–r– 3 hjl hadoop 0 2011-03-08 11:21 /hjl/sunwg_test11/attempt_201103070826_0018_r_000030_0
-rw-r–r– 3 hjl hadoop 0 2011-03-08 11:21 /hjl/sunwg_test11/attempt_201103070826_0018_r_000031_0
文件被打散后，可以启动多个mapreduce task
当执行一些操作的时候，你会发现系统启动了32个map任务。
本文转自http://www.oratea.net/?p=492