[PIG-2421] EvalFuncs need redesigned

• Type: New Feature
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Affects Version/s: 0.11
• Component/s: impl
• Assignee: Alan Gates
• Reporter: Alan Gates
• Created: 10/Dec/11 15:58
• Updated: 30/Aug/12 23:06

Description

The current EvalFunc interface (and associated Algebraic and Accumulator interfaces) have grown unwieldy. In particular, people have noted the following issues:

1. Writing a UDF requires a lot of boiler plate code.
2. Since UDFs always pass a tuple, users are required to manage their own type checking for input.
3. Declaring schemas for output data is confusing.
4. Writing a UDF that accepts multiple different parameters (using getArgToFuncMapping) is confusing.
5. Using Algebraic and Accumulator interfaces often entails duplicating code from the initial implementation.
6. UDF implementors are exposed to the internals of Pig since they have to know when to return a tuple (Initial, Intermediate) and when not to (exec, Final).
7. The separation of Initial, Intermediate, and Final into separate classes forces code duplication and makes it hard for UDFs in other languages to use those interfaces.
8. There is unused code in the current interface that occasionally causes confusion (e.g. isAsynchronous)

Any change must be done in a way that allows existing UDFs to continue working essentially forever.

Issue Links

• is related to: PIG-2430 An EvalFunc which overrides getArgToFuncMapping with FuncSpec with constructor arguments is not properly instantiated with said arguments
• is related to: PIG-2344 UDF / LoadFunc / StoreFunc should be serializable
• relates to: PIG-2699 Reduce the number of instances of Load and Store Funcs down to 2+1. It should be 1 in the front-end and 1 in the backend