Executor PlanState tree and ExecProcNode pull
Simple terms
Think of the plan as a wiring diagram and the executor as the live circuit. Each box becomes a running node. The top box keeps asking for the next row; each box asks the boxes under it only when it has to. That is why LIMIT can stop a huge sort early from the client’s point of view of rows returned, the pull stops.
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After the planner returns a Plan, what does the executor build, how do tuples move, and how do EXPLAIN ANALYZE’s loops and startup time fall out of that design?
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