> The right-anti join plan has the same cost estimation with right join > plan in this case. So would you please help to test what the right join > plan looks like in your env for the query below? > > select * from foo left join bar on foo.a = bar.c;
You're right, it does.
55432 16devel 475322=# explain (analyze, buffers) select * from foo left join bar on foo.a = bar.c; QUERY PLAN ────────────────────────────────────────────────────────────────────────────────────────────────────────────────────── Hash Right Join (cost=1.23..90875.24 rows=10 width=20) (actual time=456.410..456.415 rows=10 loops=1) Hash Cond: (bar.c = foo.a) Buffers: shared hit=15852 read=6273 -> Seq Scan on bar (cost=0.00..72124.00 rows=5000000 width=12) (actual time=0.036..210.468 rows=5000000 loops=1) Buffers: shared hit=15852 read=6272 -> Hash (cost=1.10..1.10 rows=10 width=8) (actual time=0.037..0.038 rows=10 loops=1) Buckets: 1024 Batches: 1 Memory Usage: 9kB Buffers: shared read=1 -> Seq Scan on foo (cost=0.00..1.10 rows=10 width=8) (actual time=0.022..0.026 rows=10 loops=1) Buffers: shared read=1 Planning: Buffers: shared hit=92 read=13 Planning Time: 1.077 ms Execution Time: 456.458 ms (14 filas)
Thanks for help testing. Comparing the anti join plan and the right join plan, the estimated cost and the execution time mismatch a lot. Seems the cost estimate of hashjoin path is not that precise for this case even in the unpatched codes. Maybe this is something we need to improve.
