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SQL Performance

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There are currently 2 articles with this tag. Use it when you want entries with a similar editorial angle.

Why SSDs alone cannot determine PostgreSQL random_page_cost

random_page_cost reflects assumptions about page access, including caching. Understand its relationship to seq_page_cost, physical row order, and tablespace overrides before testing a value such as 1.1.

Database Postgresql

2026-10-18

Why PostgreSQL COUNT(DISTINCT) cannot use parallel aggregation—and how to rewrite it

PostgreSQL cannot use parallel aggregation when an aggregate call contains DISTINCT. Using the primary source’s execution plans and benchmark as the starting point, this article explains a GROUP BY rewrite, NULL semantics, and what to validate with EXPLAIN.

Database Postgresql

2026-08-06