Thread: havingQual vs hasHavingQual buglets

I came across a couple of places in the planner that are checking
for nonempty havingQual; but since these bits run after
const-simplification of the HAVING clause, that produces the wrong
answer for a constant-true HAVING clause (which'll be folded to
empty).  Correct code is to check root->hasHavingQual instead.

These mistakes only affect cost estimates, and they're sufficiently
corner cases that it'd be hard even to devise a reliable test case
showing a different plan choice.  So I'm not very excited about this,
and am thinking of committing only to HEAD.

            regards, tom lane

diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index d98709e5e8..8d7500abfb 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -3357,7 +3357,7 @@ estimate_path_cost_size(PlannerInfo *root,
              * Get the retrieved_rows and rows estimates.  If there are HAVING
              * quals, account for their selectivity.
              */
-            if (root->parse->havingQual)
+            if (root->hasHavingQual)
             {
                 /* Factor in the selectivity of the remotely-checked quals */
                 retrieved_rows =
@@ -3405,7 +3405,7 @@ estimate_path_cost_size(PlannerInfo *root,
             run_cost += cpu_tuple_cost * numGroups;

             /* Account for the eval cost of HAVING quals, if any */
-            if (root->parse->havingQual)
+            if (root->hasHavingQual)
             {
                 QualCost    remote_cost;

diff --git a/src/backend/optimizer/path/allpaths.c b/src/backend/optimizer/path/allpaths.c
index 8fc28007f5..4ddaed31a4 100644
--- a/src/backend/optimizer/path/allpaths.c
+++ b/src/backend/optimizer/path/allpaths.c
@@ -2575,7 +2575,7 @@ set_subquery_pathlist(PlannerInfo *root, RelOptInfo *rel,
     if (parse->hasAggs ||
         parse->groupClause ||
         parse->groupingSets ||
-        parse->havingQual ||
+        root->hasHavingQual ||
         parse->distinctClause ||
         parse->sortClause ||
         has_multiple_baserels(root))

On Tue, Oct 18, 2022 at 9:47 AM Richard Guo <guofenglinux@gmail.com> wrote:
> On Tue, Oct 18, 2022 at 5:37 AM Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> I came across a couple of places in the planner that are checking
>> for nonempty havingQual; but since these bits run after
>> const-simplification of the HAVING clause, that produces the wrong
>> answer for a constant-true HAVING clause (which'll be folded to
>> empty).  Correct code is to check root->hasHavingQual instead.

The postgres_fdw bits would be my oversight.  :-(

> +1. root->hasHavingQual is set before we do any expression
> preprocessing. It should be the right one to check with.

+1  HEAD only seems reasonable.

Best regards,
Etsuro Fujita

Etsuro Fujita <etsuro.fujita@gmail.com> writes:
> On Tue, Oct 18, 2022 at 9:47 AM Richard Guo <guofenglinux@gmail.com> wrote:
>> On Tue, Oct 18, 2022 at 5:37 AM Tom Lane <tgl@sss.pgh.pa.us> wrote:
>>> I came across a couple of places in the planner that are checking
>>> for nonempty havingQual; but since these bits run after
>>> const-simplification of the HAVING clause, that produces the wrong
>>> answer for a constant-true HAVING clause (which'll be folded to
>>> empty).  Correct code is to check root->hasHavingQual instead.

> The postgres_fdw bits would be my oversight.  :-(

No worries --- I think the one in set_subquery_pathlist is probably
my fault :-(

> +1  HEAD only seems reasonable.

Pushed that way; thanks for looking.

            regards, tom lane