cost-based optimizer
Choose among query plans using estimated resource costs.
Use this when A join order performs badly because the database misestimates intermediate row counts.
without the term
“This join’s row estimate is far from reality. Explain how the estimated resource cost affects the chosen plan.”
with the term · How do you ask a model for cost-based optimizer?
Diagnose this cost-based optimizer estimate. Check statistics and skew, then compare plans on representative data.
What is cost-based optimizer?
A cost-based optimizer estimates candidate plan costs from statistics and a cost model. It chooses among considered plans, without a guarantee of finding the globally fastest plan.
Why does cost-based optimizer matter when vibe coding?
An agent can tune random cost settings while the actual error is stale or unrepresentative statistics.
How do you do cost-based optimizer?
Find the largest estimate-versus-actual mismatch. Check statistics, data distribution, and cost assumptions. Compare candidate plans under the same representative workload.
What goes wrong with cost-based optimizer?
Cost units are model units, not milliseconds. Correlated columns and changing workloads can defeat simple estimates.
Sources for this entry
- PostgreSQL: Using EXPLAIN
Planner estimates, cost units, actual execution statistics, and the fact that ANALYZE executes the statement.
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