[TAJO-408] Improve function system

• Type: Improvement
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 0.8.0, 0.9.0
• Component/s: Function/UDF
• Assignee: SeongHwa Ahn
• Reporter: Hyunsik Choi
• Created: 11/Dec/13 05:41
• Updated: 15/Feb/15 09:18
• Resolved: 15/Feb/15 09:18

Description

Currently, function system was designed few years ago. So, there are lack of key features necessary for functions and user-defined functions.

I have discussed this issue with epsilon. We could summary the following issues.

• There is no way to describe explanation of functions.
  • For user convenience, Tajo needs to show users function information, including signature, parameters, results, descriptions, and examples.
• TajoMaster registers lots of functions at startup time. This is a burden to maintain registration codes. We need to improve this to automatically register built-in functions in a specific package.
• Currently, the way to find matched function is too strict.
  • Due to this function match system, we have to register functions for each parameter type combination.
  • Function match mechanism should consider type compatibility. For example, count(val:integer) can be compatibly to count(val:long). In this case, we need to only register count(val:bigint) function. Tajo has to find count(val:bigint) even though count(val:integer) function is called.
• We need more elaborate UDF regestration system.
  • Currently, registering a user-defined function requires system restart. There is no way to register UDFs in runtime.
  • Tajo should provide a run-time UDF registration system.
  • It should involve user jars distribution.
  • It should provide 'CREATE FUNCTION' and 'DROP FUNCTION' statements.
  • The registration functions are stored in catalog system, and they should be loaded even though a Tajo cluster is restarted.

This is an umbrella issue. we'll create one or more sub tasks for the above issues.