Radim Marek: How TABLESAMPLE picks rows

T2Covered by 1 source · first reported by Planet PostgreSQL at 11 Oct, 18:45 UTC

Most exploratory questions against a large table only need a rough answer, but without an index on status, even "roughly how many shipped orders" costs a full scan. On the two-million-row orders table, Postgres has to read every single 8 kB page, all 18,085 of them (141 MB), just to count matching…