Part VI: Other ways to run a plan

The plan is chosen: what changes when an engine runs it another way?

Every plan so far ran the same way: each operator pulled batches from the one below it, and the top of the plan drove the run. The engines you use do not all run that way. This part takes one plan and runs it differently, and counts what the difference changes. It starts by turning the loop upside down, so that the scan pushes rows up the plan, and asks what that costs in stopping early and saves in reading once for several consumers (ch18). Last, it turns a pipeline into code before the first row is read, and counts what the interpreter no longer does, and what the code gives up in return (ch19).

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