[IMPALA-10388] Document the limitation on mask functions

• Type: Documentation
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Fix Version/s: Impala 4.0.0
• Component/s: Docs
• Epic Link: Ranger Column Masking
• Epic Color: ghx-label-11
• Assignee: shajini thayasingh
• Reporter: Quanlong Huang
• Created: 10/Dec/20 08:03
• Updated: 27/Mar/21 10:44
• Resolved: 27/Mar/21 10:44

Description

Hive's mask functions are GenericUDFs. Impala currently doesn't support Hive GenericUDFs, so we have our builtin implementation for them. Due to lack of a corresponding framework for GenericUDF in Impala (IMPALA-9271), we implement these mask functions by overloads. However, it may requires hundreds of overloads to cover all possible combinations. We just implement some important overloads, including

• those used by Ranger default masking policies,
• those with simple arguments and may be useful for users,
• an overload with all arguments in int type for full functionality. Char argument need to be converted to their ASCII value.

If you encountered errors like "No matching function with signature: mask...", it means Impala is lack of the corresponding overload. Use the following query to find the available overloads:

show functions in _impala_builtins like "mask*";