[database] iterators and joins

Pipe

SQL query -> query parser & optimizer -> relational algebra -> B+ tree indexed scan iterator

Tuple-in -> Tuple-out (dataflow graph)

Query executor instantiates operators

Iterator interface (pull based computation model)

Heap Scan

Does not have any children but call file manager for the next page.

Sort (2-passes)

Group By on Sorted Input

the implement is memory efficient while merge each group with one tuple.

Full Query Plan

Join Operators (binary operators)

Simple Nested Looks Theta Join

Page Nested Loop Join (as page block)

'Memory Chunk' Nested Loop Join