Answer
The planner evaluates possible execution paths and selects the lowest-cost plan using statistics.
Quick Answer
PostgreSQL query planner estimates the cost of different execution strategies (seq scan, index scan, hash join, nested loop) using table statistics from pg_statistic. It chooses the plan with lowest estimated cost. Cost estimates depend on: row count estimates, column value distribution, physical I/O cost settings (seq_page_cost, random_page_cost). Stale stats or bad estimates lead to poor plan choices.
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SugharaIQ Editorial Team
Verified Answer
This answer has been peer-reviewed by industry experts holding senior engineering roles to ensure technical accuracy and relevance for modern interview standards.
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Source: SugharaIQ