压缩

1 MR支持的压缩编码

为了支持多种压缩/解压缩算法，Hadoop引入了编码/解码器，如下表所示：

压缩性能的比较

http://google.github.io/snappy/

On a single core of a Core i7 processor in 64-bit mode, Snappy compresses at about 250 MB/sec or more and decompresses at about 500 MB/sec or more.

#查看hadoop支持的压缩算法
hadoop  checknative

2 压缩参数

#修改mapred-site.xml
mapreduce.map.output.compresstrue

mapreduce.map.output.compress.codecorg.apache.hadoop.io.compress.SnappyCodec


mapreduce.output.fileoutputformat.compresstrue

mapreduce.output.fileoutputformat.compress.codecorg.apache.hadoop.io.compress.SnappyCodec


mapreduce.output.fileoutputformat.compress.typeBLOCK

3 测试MR压缩

#创建目录
hadoop fs -mkdir /wc
#上传小文件
hadoop fs -put ./word.txt  /wc#执行wordcount
hadoop jar share/hadoop/mapreduce/hadoop-mapreduce-examples-3.1.3.jar wordcount /wc/word.txt  /wc/1#查看
hadoop fs -D io.compression.codec.snappy.native=true -text /wc/1/part-r-00000.snappy  |head -10

5 修改hive配置文件

vim hive-site.xml
hive.exec.compress.outputtrue

mapreduce.map.output.compress.codecorg.apache.hadoop.io.compress.SnappyCodec


mapreduce.output.fileoutputformat.compresstrue

mapreduce.output.fileoutputformat.compress.codecorg.apache.hadoop.io.compress.SnappyCodec


mapreduce.output.fileoutputformat.compress.typeBLOCK

6 重启hive，创建表，加载数据

CREATE TABLE t_test(
cookieid string,
createtime string, 
pv INT
) ROW FORMAT DELIMITED FIELDS TERMINATED BY ',';load data local inpath '/usr/local/rosh/data/test.txt' into table t_test;

7 执行sql

insert overwrite local directory '/usr/local/rosh/compress' select * from t_test distribute by cookieid sort by pv desc;