Disable asynchronous execution if using gating Result nodes.

mark_async_capable_plan(), which is called from create_append_plan() to
determine whether subplans are async-capable, failed to take into
account that the given subplan created from a given subpath might
include a gating Result node if the subpath is a SubqueryScanPath or
ForeignPath, causing a segmentation fault there when the subplan created
from a SubqueryScanPath includes the Result node, or causing
ExecAsyncRequest() to throw an error about an unrecognized node type
when the subplan created from a ForeignPath includes the Result node,
because in the latter case the Result node was unintentionally
considered as async-capable, but we don't currently support executing
Result nodes asynchronously.  Fix by modifying mark_async_capable_plan()
to disable asynchronous execution in such cases.  Also, adjust code in
the ProjectionPath case in mark_async_capable_plan(), for consistency
with other cases, and adjust/improve comments there.

is_async_capable_path() added in commit 27e1f1456, which was rewritten
to mark_async_capable_plan() in a later commit, has the same issue,
causing the error at execution mentioned above, so back-patch to v14
where the aforesaid commit went in.

Per report from Justin Pryzby.

Etsuro Fujita, reviewed by Zhihong Yu and Justin Pryzby.

Discussion: https://postgr.es/m/20220408124338.GK24419%40telsasoft.com

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 8bcc18eca61909be7e6ea0ecfbf226b42fada444..fa9674d1efa89383a63e65dcf9ae0ce4be8b20b2 100644 (file)
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -10424,6 +10424,32 @@ DROP TABLE local_tbl;
 DROP INDEX base_tbl1_idx;
 DROP INDEX base_tbl2_idx;
 DROP INDEX async_p3_idx;
+-- Disable async execution if we use gating Result nodes for pseudoconstant
+-- quals
+EXPLAIN (VERBOSE, COSTS OFF)
+SELECT * FROM async_pt WHERE CURRENT_USER = SESSION_USER;
+                           QUERY PLAN                           
+----------------------------------------------------------------
+ Append
+   ->  Result
+         Output: async_pt_1.a, async_pt_1.b, async_pt_1.c
+         One-Time Filter: (CURRENT_USER = SESSION_USER)
+         ->  Foreign Scan on public.async_p1 async_pt_1
+               Output: async_pt_1.a, async_pt_1.b, async_pt_1.c
+               Remote SQL: SELECT a, b, c FROM public.base_tbl1
+   ->  Result
+         Output: async_pt_2.a, async_pt_2.b, async_pt_2.c
+         One-Time Filter: (CURRENT_USER = SESSION_USER)
+         ->  Foreign Scan on public.async_p2 async_pt_2
+               Output: async_pt_2.a, async_pt_2.b, async_pt_2.c
+               Remote SQL: SELECT a, b, c FROM public.base_tbl2
+   ->  Result
+         Output: async_pt_3.a, async_pt_3.b, async_pt_3.c
+         One-Time Filter: (CURRENT_USER = SESSION_USER)
+         ->  Seq Scan on public.async_p3 async_pt_3
+               Output: async_pt_3.a, async_pt_3.b, async_pt_3.c
+(18 rows)
+
 -- Test that pending requests are processed properly
 SET enable_mergejoin TO false;
 SET enable_hashjoin TO false;

diff --git a/contrib/postgres_fdw/sql/postgres_fdw.sql b/contrib/postgres_fdw/sql/postgres_fdw.sql
index 855c7ea70edbbc7c17fc94b5f45121a783ee43fb..89de85c03e3353190ffdf934a639bc8b80a054c2 100644 (file)
--- a/contrib/postgres_fdw/sql/postgres_fdw.sql
+++ b/contrib/postgres_fdw/sql/postgres_fdw.sql
@@ -3317,6 +3317,11 @@ DROP INDEX base_tbl1_idx;
 DROP INDEX base_tbl2_idx;
 DROP INDEX async_p3_idx;
 
+-- Disable async execution if we use gating Result nodes for pseudoconstant
+-- quals
+EXPLAIN (VERBOSE, COSTS OFF)
+SELECT * FROM async_pt WHERE CURRENT_USER = SESSION_USER;
+
 -- Test that pending requests are processed properly
 SET enable_mergejoin TO false;
 SET enable_hashjoin TO false;

diff --git a/src/backend/optimizer/plan/createplan.c b/src/backend/optimizer/plan/createplan.c
index a2101fb3fcb6c2047a6369602ca319ea3e362348..0ed858f305a151d0383beca58c5e609e4b48ef63 100644 (file)
--- a/src/backend/optimizer/plan/createplan.c
+++ b/src/backend/optimizer/plan/createplan.c
@@ -82,7 +82,7 @@ static List *get_gating_quals(PlannerInfo *root, List *quals);
 static Plan *create_gating_plan(PlannerInfo *root, Path *path, Plan *plan,
                                List *gating_quals);
 static Plan *create_join_plan(PlannerInfo *root, JoinPath *best_path);
-static bool is_async_capable_path(Path *path);
+static bool is_async_capable_plan(Plan *plan, Path *path);
 static Plan *create_append_plan(PlannerInfo *root, AppendPath *best_path,
                                int flags);
 static Plan *create_merge_append_plan(PlannerInfo *root, MergeAppendPath *best_path,
@@ -1109,11 +1109,11 @@ create_join_plan(PlannerInfo *root, JoinPath *best_path)
 }
 
 /*
- * is_async_capable_path
- *     Check whether a given Path node is async-capable.
+ * is_async_capable_plan
+ *     Check whether the Plan node created from a Path node is async-capable.
  */
 static bool
-is_async_capable_path(Path *path)
+is_async_capable_plan(Plan *plan, Path *path)
 {
    switch (nodeTag(path))
    {
@@ -1121,6 +1121,13 @@ is_async_capable_path(Path *path)
            {
                FdwRoutine *fdwroutine = path->parent->fdwroutine;
 
+               /*
+                * If the generated plan node includes a gating Result node,
+                * we can't execute it asynchronously.
+                */
+               if (IsA(plan, Result))
+                   return false;
+
                Assert(fdwroutine != NULL);
                if (fdwroutine->IsForeignPathAsyncCapable != NULL &&
                    fdwroutine->IsForeignPathAsyncCapable((ForeignPath *) path))
@@ -1295,8 +1302,8 @@ create_append_plan(PlannerInfo *root, AppendPath *best_path, int flags)
 
        subplans = lappend(subplans, subplan);
 
-       /* Check to see if subplan can be executed asynchronously */
-       if (consider_async && is_async_capable_path(subpath))
+       /* If needed, check to see if subplan can be executed asynchronously */
+       if (consider_async && is_async_capable_plan(subplan, subpath))
        {
            subplan->async_capable = true;
            ++nasyncplans;