Code: src/backend/executor

PostgreSQL uses pipelining ...

• query plan is a tree of Plan nodes
• each type of node implements one kind of RA operation
  (node implements specific access method via iterator interface)
• node types e.g. Scan, Group, Indexscan, Sort, HashJoin
• execution is managed via a tree of PlanState nodes
  (mirrors the structure of the tree of Plan nodes; holds execution state)