On Fri, Sep 8, 2023 at 3:15 AM Robert Haas <robertmh...@gmail.com> wrote:
> The example query provided here seems rather artificial. Surely few > people write a join clause that references neither of the tables being > joined. Is there a more realistic case where this makes a big > difference? Yes the given example query is not that convincing. I tried a query with plans as below (after some GUC setting) which might be more realistic in real world. unpatched: explain select * from partsupp join lineitem on l_partkey > ps_partkey; QUERY PLAN -------------------------------------------------------------------------------------- Gather (cost=0.00..5522666.44 rows=160466667 width=301) Workers Planned: 4 -> Nested Loop (cost=0.00..5522666.44 rows=40116667 width=301) Join Filter: (lineitem.l_partkey > partsupp.ps_partkey) -> Parallel Seq Scan on lineitem (cost=0.00..1518.44 rows=15044 width=144) -> Seq Scan on partsupp (cost=0.00..267.00 rows=8000 width=157) (6 rows) patched: explain select * from partsupp join lineitem on l_partkey > ps_partkey; QUERY PLAN -------------------------------------------------------------------------------------- Gather (cost=0.00..1807085.44 rows=160466667 width=301) Workers Planned: 4 -> Nested Loop (cost=0.00..1807085.44 rows=40116667 width=301) Join Filter: (lineitem.l_partkey > partsupp.ps_partkey) -> Parallel Seq Scan on lineitem (cost=0.00..1518.44 rows=15044 width=144) -> Materialize (cost=0.00..307.00 rows=8000 width=157) -> Seq Scan on partsupp (cost=0.00..267.00 rows=8000 width=157) (7 rows) The execution time (ms) are (avg of 3 runs): unpatched: 71769.21 patched: 65510.04 So we can see some (~9%) performance gains in this case. Thanks Richard