S3 has no catalogs concept, but that does not stop us from putting / as delimiters in the object keys and think of files with the same key prefix as files in the same directory.
That causes a problem when we want to copy one catalog’s content into another because we cannot just copy files to a different location. We have to preserve parts of the object keys.
In a file system on a computer when we have those files:
/home/user/the_directory/file_A
/home/user/the_directory/file_B
/home/user/the_directory/file_C
/home/user/the_directory/file_D
and we want to copy them to the home directory of user another_user, the expected result looks like this:
/home/another_user/the_directory/file_A
/home/another_user/the_directory/file_B
/home/another_user/the_directory/file_C
/home/another_user/the_directory/file_D
How do we achieve the same outcome in S3?
We need two things:
- a running EMR cluster
- the
s3-dist-cpscript, which is available on all EMR clusters
Let’s pretend that the above directory structure is also the structure of our S3 keys. For example, we have a file in this location: s3://home/user/the_directory/file_A.
First, we have to SSH into the master node of the cluster.
After that, we run the s3-dist-cp command using the source prefix as the source and the target prefix as the destination. The script will automatically preserve the rest of the object keys:
s3-dist-cp --src=s3://home/user --dest=s3://home/another_user
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