hive中使用rcfile

（1）建student & student1 表：（hive 托管）
create table student(id INT, age INT, name STRING)
partitioned by(stat_date STRING)
clustered by(id) sorted by(age) into 4 buckets
row format delimited fields terminated by ',';

create table studentrc(id INT, age INT, name STRING)
partitioned by(stat_date STRING)
clustered by(id) sorted by(age) into 4 buckets
row format delimited fields terminated by ',' stored as rcfile;

create table studentlzo(id INT, age INT, name STRING)
partitioned by(stat_date STRING)
clustered by(id) sorted by(age) into 4 buckets
row format delimited fields terminated by ',' stored as rcfile;

文件格式 textfile， sequencefile， rcfile
（2）设置环境变量：
set hive.enforce.bucketing = true;
（3）插入数据：
  LOAD DATA local INPATH '/home/hadoop/hivetest1.txt' OVERWRITE INTO TABLE student partition(stat_date="20120802");

(CPU使用率很高)
from student
insert overwrite table student1 partition(stat_date="20120802")
select id,age,name where stat_date="20120802" sort by age;

查看数据
select id, age, name from student  distribute by id ; // distribute相当于mapreduce中的key

抽选数据(一般测试的情况下使用)
select * from student tablesample(bucket 1 out of 2 on id);
TABLESAMPLE(BUCKET x OUT OF y)
其中, x必须比y小, y必须是在创建表的时候bucket on的数量的因子或者倍数, hive会根据y的大小来决定抽样多少, 比如原本分了32分, 当y=16时, 抽取32/16=2分, 这时TABLESAMPLE(BUCKET 3 OUT OF 16) 就意味着要抽取第3和第16+3=19分的样品. 如果y=64， 这要抽取 32/64=1/2份数据, 这时TABLESAMPLE(BUCKET 3 OUT OF 64) 意味着抽取第3份数据的一半来进行.

rcfile操作

// 导入(gzip压缩)
set hive.enforce.bucketing=true;
set hive.exec.compress.output=true;  
set mapred.output.compress=true;  
set mapred.output.compression.codec=org.apache.hadoop.io.compress.GzipCodec;  
set io.compression.codecs=org.apache.hadoop.io.compress.GzipCodec;  
from student
insert overwrite table studentrc partition(stat_date="20120802")  
select id,age,name where stat_date="20120802" sort by age;

// lzo压缩
set hive.io.rcfile.record.buffer.size = 16777216; // 16 * 1024 * 1024
set io.file.buffer.size = 131072; // 缓冲区大小 128 * 1024

set hive.enforce.bucketing=true;
set hive.exec.compress.output=true;  
set mapred.output.compress=true;  
set mapred.output.compression.codec=com.hadoop.compression.lzo.LzoCodec;  
set io.compression.codecs=com.hadoop.compression.lzo.LzoCodec;  
from student
insert overwrite table studentlzo partition(stat_date="20120802")  
select id,age,name where stat_date="20120802" sort by age;

// sequencefile导入
set hive.exec.compress.output=true;  
set mapred.output.compress=true;  
set mapred.output.compression.codec=org.apache.hadoop.io.compress.GzipCodec;  
set io.compression.codecs=org.apache.hadoop.io.compress.GzipCodec;  
insert overwrite table studentseq select * from student;