This topic describes how to use the data copy tool Jindo DistCp.

Prerequisites

An EMR cluster of the 3.28.0 version or later is created. For information about how to create a cluster, see Create a cluster.

Use Jindo DistCp

Run the following command to obtain the help information:

[root@emr-header-1 opt]# jindo distcp --help

--src and --dest

--src specifies the source directory. --dest specifies the destination directory.

By default, Jindo DistCp copies all files in the directory specified by --src to the directory specified by --dest. If you do not specify a root directory, Jindo DistCp automatically creates a root directory.

For example, you can run the following command to copy files in the/opt/tmp directory of HDFS to an OSS bucket: 
jindo distcp --src /opt/tmp --dest oss://yang-hhht/tmp

--parallelism

--parallelism specifies the mapreduce.job.reduces parameter for the MapReduce job that is executed to copy files. The default value is 7. You can customize --parallelism based on your available cluster resources. This allows you to determine how many reduce tasks can be run in parallel.

For example, you can run the following command to copy files in the /opt/tmp directory of HDFS to an OSS bucket: 
jindo distcp --src /opt/tmp --dest oss://yang-hhht/tmp --parallelism 20

--srcPattern

--srcPattern specifies a regular expression that filters files for the copy operation. The regular expression must match a full path.

For example, if you need to copy all log files in the /data/incoming/hourly_table/2017-02-01/03 directory, set --srcPattern to .*\.log.

Run the following command to view the files in the /data/incoming/hourly_table/2017-02-01/03 directory: 
[root@emr-header-1 opt]# hdfs dfs -ls /data/incoming/hourly_table/2017-02-01/03
The following information is returned: 
Found 6 items
-rw-r-----   2 root hadoop       2252 2020-04-17 20:42 /data/incoming/hourly_table/2017-02-01/03/000151.sst
-rw-r-----   2 root hadoop       4891 2020-04-17 20:47 /data/incoming/hourly_table/2017-02-01/03/1.log
-rw-r-----   2 root hadoop       4891 2020-04-17 20:47 /data/incoming/hourly_table/2017-02-01/03/2.log
-rw-r-----   2 root hadoop       4891 2020-04-17 20:42 /data/incoming/hourly_table/2017-02-01/03/OPTIONS-000109
-rw-r-----   2 root hadoop       1016 2020-04-17 20:47 /data/incoming/hourly_table/2017-02-01/03/emp01.txt
-rw-r-----   2 root hadoop       1016 2020-04-17 20:47 /data/incoming/hourly_table/2017-02-01/03/emp06.txt
Run the following command to copy the log files: 
jindo distcp --src /data/incoming/hourly_table --dest oss://yang-hhht/hourly_table --srcPattern . *\.log --parallelism 20
Run the following command to view files in the destination OSS bucket: 
[root@emr-header-1 opt]# hdfs dfs -ls oss://yang-hhht/hourly_table/2017-02-01/03
The following information is returned. Only log files in the source directory are copied. 
Found 2 items
-rw-rw-rw-   1       4891 2020-04-17 20:52 oss://yang-hhht/hourly_table/2017-02-01/03/1.log
-rw-rw-rw-   1       4891 2020-04-17 20:52 oss://yang-hhht/hourly_table/2017-02-01/03/2.log

--deleteOnSuccess

--deleteOnSuccess enables Jindo DistCp to delete the copied files from the source directory after a copy operation succeeds.

For example, you can run the following command to copy files in /data/incoming/hourly_table to an OSS bucket and delete the copied files from the source directory:
jindo distcp --src /data/incoming/hourly_table --dest oss://yang-hhht/hourly_table --deleteOnSuccess --parallelism 20

--outputCodec

--outputCodec specifies the compression codec that is used to compress copied files online. Example: 

jindo distcp --src /data/incoming/hourly_table --dest oss://yang-hhht/hourly_table --outputCodec=gz --parallelism 20
Run the following command to view files in the destination directory: 
[root@emr-header-1 opt]# hdfs dfs -ls oss://yang-hhht/hourly_table/2017-02-01/03
The following information is returned. Files in the destination directory are compressed in the GZ format. 
Found 6 items
-rw-rw-rw-   1        938 2020-04-17 20:58 oss://yang-hhht/hourly_table/2017-02-01/03/000151.sst.gz
-rw-rw-rw-   1       1956 2020-04-17 20:58 oss://yang-hhht/hourly_table/2017-02-01/03/1.log.gz
-rw-rw-rw-   1       1956 2020-04-17 20:58 oss://yang-hhht/hourly_table/2017-02-01/03/2.log.gz
-rw-rw-rw-   1       1956 2020-04-17 20:58 oss://yang-hhht/hourly_table/2017-02-01/03/OPTIONS-000109.gz
-rw-rw-rw-   1        506 2020-04-17 20:58 oss://yang-hhht/hourly_table/2017-02-01/03/emp01.txt.gz
-rw-rw-rw-   1        506 2020-04-17 20:58 oss://yang-hhht/hourly_table/2017-02-01/03/emp06.txt.gz
You can set this parameter to gzip, gz, lzo, lzop, snappy, none, or keep. Default value: keep.
  • none: Jindo DistCp does not compress copied files. If the files have been compressed, Jindo DistCp decompresses them.
  • keep: Jindo DistCp copies files with no change in the compression.
Note If you want to use the LZO codec in an open source Hadoop cluster, you must install the native library of gplcompression and the hadoop-lzo package.

--outputManifest and --requirePreviousManifest

--outputManifest generates a manifest file that contains the information about all the files copied by Jindo DistCp. The information includes the destination files, source files, and file sizes.

If you want to generate a manifest file, set --requirePreviousManifest to false. By default, the file is compressed in the GZ format. This is the only supported format. 
jindo distcp --src /data/incoming/hourly_table --dest oss://yang-hhht/hourly_table --outputManifest=manifest-2020-04-17.gz --requirePreviousManifest=false --parallelism 20
Run the following command to view the content of the file: 
[root@emr-header-1 opt]# hadoop fs -text oss://yang-hhht/hourly_table/manifest-2020-04-17.gz > before.lst
[root@emr-header-1 opt]# cat before.lst
The following information is returned: 
{"path":"oss://yang-hhht/hourly_table/2017-02-01/03/000151.sst","baseName":"2017-02-01/03/000151.sst","srcDir":"oss://yang-hhht/hourly_table","size":2252}
{"path":"oss://yang-hhht/hourly_table/2017-02-01/03/1.log","baseName":"2017-02-01/03/1.log","srcDir":"oss://yang-hhht/hourly_table","size":4891}
{"path":"oss://yang-hhht/hourly_table/2017-02-01/03/2.log","baseName":"2017-02-01/03/2.log","srcDir":"oss://yang-hhht/hourly_table","size":4891}
{"path":"oss://yang-hhht/hourly_table/2017-02-01/03/OPTIONS-000109","baseName":"2017-02-01/03/OPTIONS-000109","srcDir":"oss://yang-hhht/hourly_table","size":4891}
{"path":"oss://yang-hhht/hourly_table/2017-02-01/03/emp01.txt","baseName":"2017-02-01/03/emp01.txt","srcDir":"oss://yang-hhht/hourly_table","size":1016}
{"path":"oss://yang-hhht/hourly_table/2017-02-01/03/emp06.txt","baseName":"2017-02-01/03/emp06.txt","srcDir":"oss://yang-hhht/hourly_table","size":1016}

--outputManifest and --previousManifest

--outputManifest generates a manifest file that contains a list of both previously and newly copied files. --previousManifest generates a manifest file that contains a list of previously copied files. This way, you can recreate the full history of operations and see what files are copied by the current job:

For example, two files are added to the source directory. Run the following command to copy the newly added files: 
jindo distcp --src /data/incoming/hourly_table --dest oss://yang-hhht/hourly_table --outputManifest=manifest-2020-04-18.gz --previousManifest=oss://yang-hhht/hourly_table/manifest-2020-04-17.gz --parallelism 20
Run the following command to view the copied files: 
[root@emr-header-1 opt]# hadoop fs -text oss://yang-hhht/hourly_table/manifest-2020-04-18.gz > current.lst
[root@emr-header-1 opt]# diff before.lst current.lst
The following information is returned: 
3a4,5
> {"path":"oss://yang-hhht/hourly_table/2017-02-01/03/5.log","baseName":"2017-02-01/03/5.log","srcDir":"oss://yang-hhht/hourly_table","size":4891}
> {"path":"oss://yang-hhht/hourly_table/2017-02-01/03/6.log","baseName":"2017-02-01/03/6.log","srcDir":"oss://yang-hhht/hourly_table","size":4891}

--copyFromManifest

You can use --copyFromManifest to specify a manifest file that was previously generated by --outputManifest and copy the files listed in the manifest file to the destination directory. Example:
jindo distcp --src /data/incoming/hourly_table --dest oss://yang-hhht/hourly_table --previousManifest=oss://yang-hhht/hourly_table/manifest-2020-04-17.gz --copyFromManifest --parallelism 20

--srcPrefixesFile

--srcPrefixesFile enables Jindo DistCp to copy files in multiple folders at a time.

Run the following command to view the sub-folders under hourly_table: 
[root@emr-header-1 opt]# hdfs dfs -ls oss://yang-hhht/hourly_table
The following information is returned: 
Found 4 items
drwxrwxrwx   -          0 1970-01-01 08:00 oss://yang-hhht/hourly_table/2017-02-01
drwxrwxrwx   -          0 1970-01-01 08:00 oss://yang-hhht/hourly_table/2017-02-02
Run the following command to copy all the files under hourly_table to the destination folder. A file named folders.txt is generated. It contains prefixes that correspond to each of the sub-folders under hourly_table. 
jindo distcp --src /data/incoming/hourly_table --dest oss://yang-hhht/hourly_table --srcPrefixesFile file:///opt/folders.txt --parallelism 20
Run the following command to view the content of the folders.txt file: 
[root@emr-header-1 opt]# cat folders.txt
The following information is returned: 
hdfs://emr-header-1.cluster-50466:9000/data/incoming/hourly_table/2017-02-01
hdfs://emr-header-1.cluster-50466:9000/data/incoming/hourly_table/2017-02-02

--groupBy and -targetSize

Reading a large number of small files from HDFS affects the data processing performance. Therefore, we recommend that you use Jindo DistCp to merge small files into large files of a specified size. This optimizes analysis performance and reduces costs.

Run the following command to view the files in the specified folder: 
[root@emr-header-1 opt]# hdfs dfs -ls /data/incoming/hourly_table/2017-02-01/03
The following information is returned: 
Found 8 items
-rw-r-----   2 root hadoop       2252 2020-04-17 20:42 /data/incoming/hourly_table/2017-02-01/03/000151.sst
-rw-r-----   2 root hadoop       4891 2020-04-17 20:47 /data/incoming/hourly_table/2017-02-01/03/1.log
-rw-r-----   2 root hadoop       4891 2020-04-17 20:47 /data/incoming/hourly_table/2017-02-01/03/2.log
-rw-r-----   2 root hadoop       4891 2020-04-17 21:08 /data/incoming/hourly_table/2017-02-01/03/5.log
-rw-r-----   2 root hadoop       4891 2020-04-17 21:08 /data/incoming/hourly_table/2017-02-01/03/6.log
-rw-r-----   2 root hadoop       4891 2020-04-17 20:42 /data/incoming/hourly_table/2017-02-01/03/OPTIONS-000109
-rw-r-----   2 root hadoop       1016 2020-04-17 20:47 /data/incoming/hourly_table/2017-02-01/03/emp01.txt
-rw-r-----   2 root hadoop       1016 2020-04-17 20:47 /data/incoming/hourly_table/2017-02-01/03/emp06.txt
Run the following command to merge the TXT files in the folder into files each with a size of no more than 10 MB: 
jindo distcp --src /data/incoming/hourly_table --dest oss://yang-hhht/hourly_table --targetSize=10 --groupBy='.*/([a-z]+). *.txt' --parallelism 20
Run the following command to view the files in the destination directory. The two TXT files are merged into one. 
[root@emr-header-1 opt]# hdfs dfs -ls oss://yang-hhht/hourly_table/2017-02-01/03/
Found 1 items
-rw-rw-rw-   1       2032 2020-04-17 21:18 oss://yang-hhht/hourly_table/2017-02-01/03/emp2

--enableBalancePlan

If both small and large files are to be copied but the file sizes are not significantly different among small files and among large files, you can use --enableBalancePlan to optimize the job allocation plan. This improves the copy performance of Jindo DistCp. If you do not specify an application plan, files are randomly allocated. 
jindo distcp --src /data/incoming/hourly_table --dest oss://yang-hhht/hourly_table --enableBalancePlan --parallelism 20
Note You cannot use this option in the same command as --groupby or --targetSize.

--enableDynamicPlan

If the files to be copied are significantly different in size and most of the files are small files, you can use --enableDynamicPlan to optimize the job allocation plan. This improves the copy performance of Jindo DistCp. 
jindo distcp --src /data/incoming/hourly_table --dest oss://yang-hhht/hourly_table --enableDynamicPlan --parallelism 20
Note You cannot use this option in the same command as --groupby or --targetSize.

--enableTransaction

--enableTransaction ensures the integrity of job levels and transaction support among jobs. Example: 

jindo distcp --src /data/incoming/hourly_table --dest oss://yang-hhht/hourly_table --enableTransaction --parallelism 20

--diff

After files are copied, you can use --diff to check the differences between the source and destination directories.

Example:
jindo distcp --src /data/incoming/hourly_table --dest oss://yang-hhht/hourly_table --diff
If all files are copied, the following information is returned: 
INFO distcp.JindoDistCp: distcp has been done completely
If some files are not copied, a manifest file that contains a list of these files is generated in the destination directory. Then, you can use --copyFromManifest and --previousManifest to copy the files in the list to the destination directory. This way, the data volume and file quantity are verified. If Jindo DistCp has performed compression or decompression operations during the copy process, --diff does not return accurate file size differences. 
jindo distcp --src /data/incoming/hourly_table --dest oss://yang-hhht/hourly_table --dest oss://yang-hhht/hourly_table --previousManifest=file:///opt/manifest-2020-04-17.gz --copyFromManifest --parallelism 20
Note If your destination directory is an HDFS directory, you must specify --dest in the format of /path, hdfs://hostname:ip/path, or hdfs://headerIp:ip/path. Other formats, such as hdfs:///path and hdfs:/path, are not supported.

Check DistCp Counters

Run the following commands to check DistCp Counters in the counter information of MapReduce: 
Distcp Counters
        Bytes Destination Copied=11010048000
        Bytes Source Read=11010048000
        Files Copied=1001

Shuffle Errors
        BAD_ID=0
        CONNECTION=0
        IO_ERROR=0
        WRONG_LENGTH=0
        WRONG_MAP=0
        WRONG_REDUCE=0
Note If Jindo DistCp has performed compression or decompression operations during the copy process, the values of Bytes Destination Copied and Bytes Source Read may be different.

Use an AccessKey pair to access OSS

If you want to access OSS from an instance outside EMR or AccessKey-free access is not supported, you can use an AccessKey pair to access OSS. Set the --ossKey, --ossSecret, and --ossEndPoint parameters in the command to specify an AccessKey pair.

Example:
jindo distcp --src /data/incoming/hourly_table --dest oss://<your_bucket>/hourly_table --ossSecret yourkey --secret yoursecret --ossEndPoint oss-cn-hangzhou.aliyuncs.com --parallelism 20

Write data into OSS in IA or Archive mode

When you use a Distcp task to write data into OSS, you can write data in Archive or Infrequent Access (IA) mode.
  • Example of the Archive mode (--archive):
    jindo distcp --src /data/incoming/hourly_table --dest oss://<your_bucket>/hourly_table --policy archive --parallelism 20
  • Example of the IA mode (--ia):
    jindo distcp --src /data/incoming/hourly_table --dest oss://<your_bucket>/hourly_table --policy ia --parallelism 20

Clean up residual files

When you run a DistCp task, files that are not correctly uploaded may be generated in your destination directory. The files are managed by OSS based on uploadId and may be invisible to users. In this case, you can specify the --cleanUpPending parameter in the command. This way, the system automatically cleans up the residual files after the task is completed. Alternatively, you can also clean up the files in the OSS console.

Example:
jindo distcp --src /data/incoming/hourly_table --dest oss://<your_bucket>/hourly_table --cleanUpPending --parallelism 20