| Parameter |
Description |
Default |
vs page read |
| seq_page_cost |
cost of sequentially fetched disk page. |
1.00 |
|
| random_page_cost |
cost of nonsequentially fetched disk page. |
4.00 |
4x slower |
| cpu_tuple_cost |
cost of processing each tuple (row). |
0.01 |
100x faster |
| cpu_operator_cost |
cost of processing each operator or function call. |
0.0025 |
400x faster |
| cpu_index_tuple_cost |
cost of processing each index entry during an index scan. |
0.005 |
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.
