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Revert commit 66c0185a3 and follow-on patches.

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This reverts 66c0185a3 (Allow planner to use Merge Append to
efficiently implement UNION) as well as the follow-on commits
d5d2205c8, 3b1a7eb28, 7487044d6.  In addition to those, 07746a8ef
had to be removed then re-applied in a different place, because
66c0185a3 moved the relevant code.

The reason for this last-minute thrashing is that depesz found a
case in which the patched code creates a completely wrong plan
that silently gives incorrect query results.  It's unclear what
the cause is or how many cases are affected, but with beta1 wrap
staring us in the face, there's no time for closer investigation.
After we figure that out, we can decide whether to un-revert this
for beta2 or hold it for v18.

Discussion: https://postgr.es/m/Zktzf926vslR35Fv@depesz.com
(also some private discussion among pgsql-release)
This commit is contained in:
Tom Lane
2024-05-20 15:08:30 -04:00
parent d2a04470aa
commit 7204f35919
18 changed files with 287 additions and 761 deletions
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61
src/backend/optimizer/path/equivclass.c
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@@ -2882,67 +2882,6 @@ add_child_join_rel_equivalences(PlannerInfo *root,
MemoryContextSwitchTo(oldcontext);
}
/*
* add_setop_child_rel_equivalences
* Add equivalence members for each non-resjunk target in 'child_tlist'
* to the EquivalenceClass in the corresponding setop_pathkey's pk_eclass.
*
* 'root' is the PlannerInfo belonging to the top-level set operation.
* 'child_rel' is the RelOptInfo of the child relation we're adding
* EquivalenceMembers for.
* 'child_tlist' is the target list for the setop child relation. The target
* list expressions are what we add as EquivalenceMembers.
* 'setop_pathkeys' is a list of PathKeys which must contain an entry for each
* non-resjunk target in 'child_tlist'.
*/
void
add_setop_child_rel_equivalences(PlannerInfo *root, RelOptInfo *child_rel,
List *child_tlist, List *setop_pathkeys)
{
ListCell *lc;
ListCell *lc2 = list_head(setop_pathkeys);
foreach(lc, child_tlist)
{
TargetEntry *tle = lfirst_node(TargetEntry, lc);
EquivalenceMember *parent_em;
PathKey *pk;
if (tle->resjunk)
continue;
if (lc2 == NULL)
elog(ERROR, "too few pathkeys for set operation");
pk = lfirst_node(PathKey, lc2);
parent_em = linitial(pk->pk_eclass->ec_members);
/*
* We can safely pass the parent member as the first member in the
* ec_members list as this is added first in generate_union_paths,
* likewise, the JoinDomain can be that of the initial member of the
* Pathkey's EquivalenceClass.
*/
add_eq_member(pk->pk_eclass,
tle->expr,
child_rel->relids,
parent_em->em_jdomain,
parent_em,
exprType((Node *) tle->expr));
lc2 = lnext(setop_pathkeys, lc2);
}
/*
* transformSetOperationStmt() ensures that the targetlist never contains
* any resjunk columns, so all eclasses that exist in 'root' must have
* received a new member in the loop above. Add them to the child_rel's
* eclass_indexes.
*/
child_rel->eclass_indexes = bms_add_range(child_rel->eclass_indexes, 0,
list_length(root->eq_classes) - 1);
}
/*
* generate_implied_equalities_for_column