||vs page read |
|| cost of sequentially fetched disk page.
|| cost of nonsequentially fetched disk page.
|| 4x slower|
|| cost of processing each tuple (row).
|| 100x faster|
|| cost of processing each operator or function call.
|| 400x faster|
|| cost of processing each index entry during an index scan.
|| 1000x faster|
•Costs are estimates of the time a node is expected to take
•By default costs are in units of “time a sequential 8kb block read takes”
•Each node has two costs, “startup” cost and “total” cost
•Costs cumulative – parents assume their children's costs
•Optimizer selects plans based on overall lowest startup and total cost
위 5가지 패러미터가 옵티마이저 플랜 수립에 직접적 영향을 주는 핵심 패러미터들입니다.
SQL 튜닝 전문가라면 반드시 살펴봐야할 패러미터들입니다.