avamingli commented on PR #1261:
URL: https://github.com/apache/cloudberry/pull/1261#issuecomment-3135176616
Fix cases where window function operations that couldn't be parallel before
can now be parallel in CBDB, such as window functions within subqueries.
In UPSTREAM select_parallel.sql
> -- Window function calculation can't be pushed to workers.
```sql
explain (costs off, verbose)
select count(*) from tenk1 a where (unique1, two) in
(select unique1, row_number() over() from tenk1 b);
QUERY PLAN
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Finalize Aggregate
Output: count(*)
-> Gather Motion 6:1 (slice1; segments: 6)
Output: (PARTIAL count(*))
-> Partial Aggregate
Output: PARTIAL count(*)
-> Parallel Hash Semi Join
Hash Cond: ((a.unique1 = b.unique1) AND (a.two =
(row_number() OVER (?))))
-> Parallel Seq Scan on public.tenk1 a
Output: a.unique1, a.unique2, a.two, a.four,
a.ten, a.twenty, a.hundred, a.thousand, a.twothousand, a.fivethous, a.tenthous,
a.odd, a.even, a.stringu1, a.stringu2, a.string4
-> Parallel Hash
Output: b.unique1, (row_number() OVER (?))
-> Redistribute Motion 1:6 (slice2; segments: 1)
Output: b.unique1, (row_number() OVER (?))
Hash Key: b.unique1
Hash Module: 3
-> WindowAgg
Output: b.unique1, row_number() OVER
(?)
-> Gather Motion 6:1 (slice3;
segments: 6)
Output: b.unique1
-> Parallel Seq Scan on
public.tenk1 b
Output: b.unique1
Settings: enable_parallel = 'on', min_parallel_table_scan_size = '0',
optimizer = 'off', parallel_setup_cost = '0', parallel_tuple_cost = '0'
Optimizer: Postgres query optimizer
(24 rows)
```
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