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Improve planner's handling of SetOp plans.

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Remove the code for inserting flag columns in the inputs of a SetOp.
That was the only reason why there would be resjunk columns in a
set-operations plan tree, so we can get rid of some code that
supported that, too.

Get rid of choose_hashed_setop() in favor of building Paths for
the hashed and sorted alternatives, and letting them fight it out
within add_path().

Remove set_operation_ordered_results_useful(), which was giving wrong
answers due to examining the wrong ancestor node: we need to examine
the immediate SetOperationStmt parent not the topmost node.  Instead
make each caller of recurse_set_operations() pass down the relevant
parent node.  (This thinko seems to have led only to wasted planning
cycles and possibly-inferior plans, not wrong query answers.  Perhaps
we should back-patch it, but I'm not doing so right now.)

Teach generate_nonunion_paths() to consider pre-sorted inputs for
sorted SetOps, rather than always generating a Sort node.

Patch by me; thanks to Richard Guo and David Rowley for review.

Discussion: https://postgr.es/m/1850138.1731549611@sss.pgh.pa.us
This commit is contained in:
Tom Lane
2024-12-19 17:02:25 -05:00
parent 2762792952
commit 8d96f57d5c
8 changed files with 365 additions and 332 deletions
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32
src/test/regress/sql/subselect.sql
View File

@ -638,8 +638,11 @@ select sum(ss.tst::int) from
where o.ten = 0;
--
-- Test rescan of a SetOp node
-- Test rescan of a hashed SetOp node
--
begin;
set local enable_sort = off;
explain (costs off)
select count(*) from
onek o cross join lateral (
@ -657,6 +660,33 @@ select count(*) from
) ss
where o.ten = 1;
rollback;
--
-- Test rescan of a sorted SetOp node
--
begin;
set local enable_hashagg = off;
explain (costs off)
select count(*) from
onek o cross join lateral (
select * from onek i1 where i1.unique1 = o.unique1
except
select * from onek i2 where i2.unique1 = o.unique2
) ss
where o.ten = 1;
select count(*) from
onek o cross join lateral (
select * from onek i1 where i1.unique1 = o.unique1
except
select * from onek i2 where i2.unique1 = o.unique2
) ss
where o.ten = 1;
rollback;
--
-- Test rescan of a RecursiveUnion node
--