[Hadoop]Hadoop Archives

1. 什么是Hadoop archives?

Hadoop archives是特殊的档案格式。一个Hadoop archive对应一个文件系统目录。 Hadoop archive的扩展名是*.har。Hadoop archive包含元数据（形式是_index和_masterindx）和数据（part-*）文件。_index文件包含了档案中的文件的文件名和位置信息。

2. 如何创建archive?

2.1 格式

hadoop archive -archiveName name -p <parent> <src>* <dest>

2.2 参数

（1）由-archiveName选项指定你要创建的archive的名字（name）。比如user_order.har。archive的名字的扩展名应该是*.har

（2）-p参数指定文件存档文件（src）的相对路径，举个例子：

-p /foo/bar a/b/c e/f/g

这里的/foo/bar是a/b/c与e/f/g的父路径，所以完整路径为/foor/bar/a/b/c与/foo/bar/e/f/g

（3）src 是输入归档文件的目录

（4）dest 是目标目录，创建的archive会保存到该目录下

2.3 Example

 hadoop archive -archiveName user_order.har -p /user/xiaosi user/user_active_new_user order/entrance_order test/archive

在上面的例子中， /user/xiaosi/user/user_active_new_user 和 /user/xiaosi/order/entrance_order 会被归档到test/aarchive/user_order.har。当创建archive时，源文件不会被更改或删除。

注意创建archives是一个Map/Reduce job。你应该在map reduce集群上运行这个命令：

xiaosi@yoona:~/opt/hadoop-2.7.3$ hadoop archive -archiveName user_order.har -p /user/xiaosi user/user_active_new_user order/entrance_order test/archive
16/12/26 20:45:36 INFO Configuration.deprecation: session.id is deprecated. Instead, use dfs.metrics.session-id
16/12/26 20:45:36 INFO jvm.JvmMetrics: Initializing JVM Metrics with processName=JobTracker, sessionId=
16/12/26 20:45:37 INFO jvm.JvmMetrics: Cannot initialize JVM Metrics with processName=JobTracker, sessionId= - already initialized
16/12/26 20:45:37 INFO jvm.JvmMetrics: Cannot initialize JVM Metrics with processName=JobTracker, sessionId= - already initialized
16/12/26 20:45:37 INFO mapreduce.JobSubmitter: number of splits:1
16/12/26 20:45:37 INFO mapreduce.JobSubmitter: Submitting tokens for job: job_local133687258_0001
16/12/26 20:45:37 INFO mapreduce.Job: The url to track the job: http://localhost:8080/
16/12/26 20:45:37 INFO mapreduce.Job: Running job: job_local133687258_0001
...
16/12/26 20:45:38 INFO mapred.LocalJobRunner: reduce task executor complete.
16/12/26 20:45:39 INFO mapreduce.Job:  map 100% reduce 100%
16/12/26 20:45:39 INFO mapreduce.Job: Job job_local133687258_0001 completed successfully
16/12/26 20:45:39 INFO mapreduce.Job: Counters: 35
File System Counters
FILE: Number of bytes read=95398
FILE: Number of bytes written=678069
FILE: Number of read operations=0
FILE: Number of large read operations=0
FILE: Number of write operations=0
HDFS: Number of bytes read=974540
HDFS: Number of bytes written=975292
HDFS: Number of read operations=55
HDFS: Number of large read operations=0
HDFS: Number of write operations=11
Map-Reduce Framework
Map input records=8
Map output records=8
Map output bytes=761
Map output materialized bytes=783
Input split bytes=147
Combine input records=0
Combine output records=0
Reduce input groups=8
Reduce shuffle bytes=783
Reduce input records=8
Reduce output records=0
Spilled Records=16
Shuffled Maps =1
Failed Shuffles=0
Merged Map outputs=1
GC time elapsed (ms)=0
Total committed heap usage (bytes)=593494016
Shuffle Errors
BAD_ID=0
CONNECTION=0
IO_ERROR=0
WRONG_LENGTH=0
WRONG_MAP=0
WRONG_REDUCE=0
File Input Format Counters 
Bytes Read=689
File Output Format Counters 
Bytes Written=0

3. 如何查看archives中的文件?

archive作为文件系统层暴露给外界。所以所有的fs shell命令都能在archive上运行，但是要使用不同的URI。 另外，archive是不可改变的。所以重命名，删除和创建都会返回错误。

Hadoop Archives 的URI是

har://scheme-hostname:port/archivepath/fileinarchive

如果没提供scheme-hostname，它会使用默认的文件系统。这种情况下URI是这种形式

har:///archivepath/fileinarchive

获得创建的archive中的文件列表，使用命令

hadoop dfs -ls har:///user/xiaosi/test/archive/user_order.har

Example：

xiaosi@yoona:~/opt/hadoop-2.7.3$ hadoop dfs -ls har:///user/xiaosi/test/archive/user_order.har
DEPRECATED: Use of this script to execute hdfs command is deprecated.
Instead use the hdfs command for it.
Found 2 items
drwxr-xr-x   - xiaosi supergroup          0 2016-12-13 13:39 har:///user/xiaosi/test/archive/user_order.har/order
drwxr-xr-x   - xiaosi supergroup          0 2016-12-24 15:51 har:///user/xiaosi/test/archive/user_order.har/user

查看archive中的entrance_order.txt文件的命令：

hadoop dfs -cat har:///user/xiaosi/test/archive/user_order.har/order/entrance_order/entrance_order.txt

Example：

xiaosi@yoona:~/opt/hadoop-2.7.3$ hadoop dfs -cat har:///user/xiaosi/test/archive/user_order.har/order/entrance_order/entrance_order.txt
DEPRECATED: Use of this script to execute hdfs command is deprecated.
Instead use the hdfs command for it.
{"clickTime":"20161210 14:47:35.000","entrance":"306","actionTime":"20161210 14:48:14.000","orderId":"21014149","businessType":"TRAIN","gid":"1B369BF1D","uid":"8661840271741","vid":"01151","income":105.5,"status":140}
{"clickTime":"20161210 14:47:35.000","entrance":"306","actionTime":"20161210 14:48:18.000","orderId":"121818e46","businessType":"TRAIN","gid":"69BF1D","uid":"86618471741","vid":"01151","income":105.5,"status":140

参考：https://hadoop.apache.org/docs/r1.2.1/hadoop_archives.html