We have used EvalNode for two purposes:
- logical planning of expressions
- evaluation of expressions
EvalNode still is very nice for the purpose of logical planning. But, each EvalNode tree takes Datum included in a tuple and results in a Datum as a evaluation result.
So, the current approach requires many object creations, and causes interpret overheads, meaning that each one evaluation involves tree traverses and many function calls. interpretation involves also many branches, and it is harmful to CPU pipelining.
I propose Java byte code generation for each expression, and I'll use ASM (http://asm.ow2.org/) for it. This approach will write native java byte code, eliminating many condition branches and function calls. In addition, it is easier to deal with java primitive data types for expressions.