The new encryption support on HDFS makes Hive incompatible and unusable when this feature is used.
HDFS encryption is designed so that an user can configure different encryption zones (or directories) for multi-tenant environments. An encryption zone has an exclusive encryption key, such as AES-128 or AES-256. Because of security compliance, the HDFS does not allow to move/rename files between encryption zones. Renames are allowed only inside the same encryption zone. A copy is allowed between encryption zones.
HDFS-6134 for more details about HDFS encryption design.
Hive currently uses a scratch directory (like /tmp/$user/$random). This scratch directory is used for the output of intermediate data (between MR jobs) and for the final output of the hive query which is later moved to the table directory location.
If Hive tables are in different encryption zones than the scratch directory, then Hive won't be able to renames those files/directories, and it will make Hive unusable.
To handle this problem, we can change the scratch directory of the query/statement to be inside the same encryption zone of the table directory location. This way, the renaming process will be successful.
Also, for statements that move files between encryption zones (i.e. LOAD DATA), a copy may be executed instead of a rename. This will cause an overhead when copying large data files, but it won't break the encryption on Hive.
Another security thing to consider is when using joins selects. If Hive joins different tables with different encryption key strengths, then the results of the select might break the security compliance of the tables. Let's say two tables with 128 bits and 256 bits encryption are joined, then the temporary results might be stored in the 128 bits encryption zone. This will conflict with the table encrypted with 256 bits temporary.
To fix this, Hive should be able to select the scratch directory that is more secured/encrypted in order to save the intermediate data temporary with no compliance issues.
- This should use a scratch directory (or staging directory) inside the table-aes256 table location.
- This should use a scratch directory inside the table-aes1 location.
- This should use a scratch directory on each of the tables locations.
- The first SELECT will have its scratch directory on table-aes128 directory.
- The second SELECT will have its scratch directory on table-aes256 directory.