Model
Share a subexpression or recompute it
The deciding input is recurrence, not compute cost, and recurrence is a property of people, not of data.
- Consumers
- consumers of the result
Worked examples, recomputed
Every number the mechanisms quote for this relationship is recomputed from it, so none of them disagrees with it.
- a 2 s scan, k = 2: 2 against 3 + 2 = 5 → recompute
- a 120 s subplan, k = 3: 240 against 10 + 3 × 2 = 16 → cache
Where it appears
Each mechanism states it in its own names. The general symbol each name stands for is shown with it.
- Query Planning & Optimization
How does a system choose a plan for a question when the facts that decide the best plan are unknown until the plan has run?