PostgreSQL 19 features an advanced query planner that utilizes table statistics from pg_statistic, gathered during the ANALYZE process, to generate and evaluate potential query plans based on their costs. The planner assesses various configurations, especially in complex joins, to select the most efficient option. Instances of poor planning are treated as bugs and addressed promptly. To improve query performance, users are advised to refresh statistics with ANALYZE, use CREATE STATISTICS for column correlations, modify indexes, and adjust memory settings. In cases where the query cannot be altered, providing planner advice may be necessary, particularly when the planner misestimates the output of PL/pgSQL functions or other custom functions, leading to inefficient query execution.