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Fix usage of the parse tree for estimate_num_groups() in set operations

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recurse_set_operations() uses the parse tree for the group number estimation,
because of the "varno 0" hack.  At the same time 2489d76c49 made root->parse
and corresponding parent_root->simple_rte_array[]->subquery distinct copies
of the parse tree, while d3d55ce571 introduced self-join removal replacing
relid of removed relation only in one of the copies.

The present commit fixes this bug by making recurse_set_operations() call
estimate_num_groups() with the copy of the parse tree processed by self-join
removal.

In future, we may think about maintaining just one copy of the parse tree
and/or keeping removed relids as aliases.

Reported-by: Zuming Jiang
Bug: #18170
Discussion: https://postgr.es/m/flat/18170-f1d17bf9a0d58b24%40postgresql.org
Author: Richard Guo, Alexander Korotkov
Reviewed-by: Andrei Lepikhov
This commit is contained in:
Alexander Korotkov
2023-11-04 03:30:18 +02:00
parent a237a07d53
commit ec63622c03
3 changed files with 29 additions and 2 deletions
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7
src/backend/optimizer/prep/prepunion.c
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@@ -324,7 +324,7 @@ recurse_set_operations(Node *setOp, PlannerInfo *root,
* anyway; otherwise do statistical estimation.
*
* XXX you don't really want to know about this: we do the estimation
* using the subquery's original targetlist expressions, not the
* using the subroot->parse's original targetlist expressions, not the
* subroot->processed_tlist which might seem more appropriate. The
* reason is that if the subquery is itself a setop, it may return a
* processed_tlist containing "varno 0" Vars generated by
@@ -332,6 +332,9 @@ recurse_set_operations(Node *setOp, PlannerInfo *root,
* mightily. We ought to get rid of the "varno 0" hack, but that
* requires a redesign of the parsetree representation of setops, so
* that there can be an RTE corresponding to each setop's output.
* Note, we use this not subquery's targetlist but subroot->parse's
* targetlist, because it was revised by self-join removal. subquery's
* targetlist might contain the references to the removed relids.
*/
if (pNumGroups)
{
@@ -341,7 +344,7 @@ recurse_set_operations(Node *setOp, PlannerInfo *root,
*pNumGroups = subpath->rows;
else
*pNumGroups = estimate_num_groups(subroot,
get_tlist_exprs(subquery->targetList, false),
get_tlist_exprs(subroot->parse->targetList, false),
subpath->rows,
NULL,
NULL);