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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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9
src/test/regress/sql/union.sql
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@ -134,10 +134,15 @@ select count(*) from
select count(*) from
( select unique1 from tenk1 intersect select fivethous from tenk1 ) ss;
-- this query will prefer a sorted setop unless we force it.
set enable_indexscan to off;
explain (costs off)
select unique1 from tenk1 except select unique2 from tenk1 where unique2 != 10;
select unique1 from tenk1 except select unique2 from tenk1 where unique2 != 10;
reset enable_indexscan;
-- the hashed implementation is sensitive to child plans' tuple slot types
explain (costs off)
select * from int8_tbl intersect select q2, q1 from int8_tbl order by 1, 2;
@ -162,6 +167,10 @@ explain (costs off)
select unique1 from tenk1 except select unique2 from tenk1 where unique2 != 10;
select unique1 from tenk1 except select unique2 from tenk1 where unique2 != 10;
explain (costs off)
select f1 from int4_tbl union all
(select unique1 from tenk1 union select unique2 from tenk1);
reset enable_hashagg;
-- non-hashable type