Re: Possible regression in PG18 beta1

>
> Yes, this is intentional as of 95dbd827f2edc
>
Thanks!

> >> > * Changing the table from TEMP to UNLOGGED makes both versions use
> >> > "Parallel Seq Scan", with PG18 being ~25% faster. (190ms vs. 150ms).
>
> I'll be curious about tests with a normal table as well with a
> sufficiently large shared_buffers.
>

Here are results for a normal table with default shared_buffers (128 MB)
and large shared_buffers (4GB):

==== PG17.5, shared_buffers=128MB ======
QUERY PLAN
------------------------------------------------------
Gather (actual rows=1 loops=1)
Workers Planned: 2
Workers Launched: 2
Buffers: shared hit=3584 read=50496
-> Parallel Seq Scan on t (actual rows=0 loops=3)
Filter: (k = 1)
Rows Removed by Filter: 3333333
Buffers: shared hit=3584 read=50496
Settings: random_page_cost = '1.1'
Planning Time: 0.119 ms
Execution Time: 141.374 ms
(11 rows)

==== PG17.5, shared_buffers=4GB ======
select * from t where k = 1;
QUERY PLAN
------------------------------------------------------
Gather (actual rows=1 loops=1)
Workers Planned: 2
Workers Launched: 2
Buffers: shared hit=3872 read=50208
-> Parallel Seq Scan on t (actual rows=0 loops=3)
Filter: (k = 1)
Rows Removed by Filter: 3333333
Buffers: shared hit=3872 read=50208
Settings: random_page_cost = '1.1'
Planning Time: 0.118 ms
Execution Time: 141.846 ms
(11 rows)

==== PG18 beta1, shared_buffers=128MB ======
QUERY PLAN
---------------------------------------------------------
Gather (actual rows=1.00 loops=1)
Workers Planned: 2
Workers Launched: 2
Buffers: shared hit=15986 read=38094
-> Parallel Seq Scan on t (actual rows=0.33 loops=3)
Filter: (k = 1)
Rows Removed by Filter: 3333333
Buffers: shared hit=15986 read=38094
Settings: random_page_cost = '1.1'
Planning Time: 0.123 ms
Execution Time: 110.650 ms
(11 rows)

==== PG18 beta1, shared_buffers=4GB ======
QUERY PLAN
---------------------------------------------------------
Gather (actual rows=1.00 loops=1)
Workers Planned: 2
Workers Launched: 2
Buffers: shared hit=15991 read=38089
-> Parallel Seq Scan on t (actual rows=0.33 loops=3)
Filter: (k = 1)
Rows Removed by Filter: 3333333
Buffers: shared hit=15991 read=38089
Settings: random_page_cost = '1.1'
Planning Time: 0.095 ms
Execution Time: 109.073 ms
(11 rows)

Best Regards,
Sadeq Dousti