On Sat, Mar 23, 2013 at 8:12 PM, Misa Simic <misa.simic@xxxxxxxxx> wrote: > but problem is - we don't know the thing id - we know calc_id: > > EXPLAIN ANALYZE > SELECT * FROM t2_left_t3_volatile v INNER JOIN t1 USING (thing_id) > WHERE calc_id = 20 With this query you've got to scan all three tables. The calc_id qual can only be pushed down into the scan on t1, so you need the whole t2/t3 join product. > EXPLAIN ANALYZE > SELECT v.no_index FROM t2_left_t3 v INNER JOIN t1 USING (thing_id) > WHERE calc_id = 20 With this query you only need to scan 2 tables. The join between t2 and t3 is eliminated by the join removal code in favor of scanning only t2, as shown in the plan you included: > "Nested Loop (cost=437.49..13047.74 rows=12111 width=4) (actual > time=6.360..71.818 rows=12038 loops=1)" > " -> Seq Scan on t1 (cost=0.00..2.25 rows=1 width=4) (actual > time=0.016..0.024 rows=1 loops=1)" > " Filter: (calc_id = 20)" > " Rows Removed by Filter: 99" > " -> Bitmap Heap Scan on t2 (cost=437.49..12924.38 rows=12111 width=12) > (actual time=6.330..69.063 rows=12038 loops=1)" > " Recheck Cond: (thing_id = t1.thing_id)" > " -> Bitmap Index Scan on t5_c2_idx (cost=0.00..434.46 rows=12111 > width=0) (actual time=4.372..4.372 rows=12038 loops=1)" > " Index Cond: (thing_id = t1.thing_id)" > "Total runtime: 72.461 ms" The difference is that this query has only one column in its target list, not *. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
