Disallow replacing joins with scans in problematic cases.

Commit e7cb7ee14, which introduced the infrastructure for FDWs and
custom scan providers to replace joins with scans, failed to add support
handling of pseudoconstant quals assigned to replaced joins in
createplan.c, leading to an incorrect plan without a gating Result node
when postgres_fdw replaced a join with such a qual.

To fix, we could add the support by 1) modifying the ForeignPath and
CustomPath structs to store the list of RestrictInfo nodes to apply to
the join, as in JoinPaths, if they represent foreign and custom scans
replacing a join with a scan, and by 2) modifying create_scan_plan() in
createplan.c to use that list in that case, instead of the
baserestrictinfo list, to get pseudoconstant quals assigned to the join;
but #1 would cause an ABI break.  So fix by modifying the infrastructure
to just disallow replacing joins with such quals.

Back-patch to all supported branches.

Reported by Nishant Sharma.  Patch by me, reviewed by Nishant Sharma and
Richard Guo.

Discussion: https://postgr.es/m/CADrsxdbcN1vejBaf8a%2BQhrZY5PXL-04mCd4GDu6qm6FigDZd6Q%40mail.gmail.com

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index f16f1447ee23593945aa0e2ebd7dc95a639306af..f06437800e200d5a5faa244c399bc3b4c9ae4e22 100644 (file)
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -2197,6 +2197,32 @@ SELECT t1."C 1" FROM "S 1"."T 1" t1, LATERAL (SELECT DISTINCT t2.c1, t3.c1 FROM
    1
 (10 rows)
 
+-- join with pseudoconstant quals, not pushed down.
+EXPLAIN (VERBOSE, COSTS OFF)
+SELECT t1.c1, t2.c1 FROM ft1 t1 JOIN ft2 t2 ON (t1.c1 = t2.c1 AND CURRENT_USER = SESSION_USER) ORDER BY t1.c3, t1.c1 OFFSET 100 LIMIT 10;
+                                  QUERY PLAN                                   
+-------------------------------------------------------------------------------
+ Limit
+   Output: t1.c1, t2.c1, t1.c3
+   ->  Sort
+         Output: t1.c1, t2.c1, t1.c3
+         Sort Key: t1.c3, t1.c1
+         ->  Result
+               Output: t1.c1, t2.c1, t1.c3
+               One-Time Filter: (CURRENT_USER = SESSION_USER)
+               ->  Hash Join
+                     Output: t1.c1, t1.c3, t2.c1
+                     Hash Cond: (t2.c1 = t1.c1)
+                     ->  Foreign Scan on public.ft2 t2
+                           Output: t2.c1
+                           Remote SQL: SELECT "C 1" FROM "S 1"."T 1"
+                     ->  Hash
+                           Output: t1.c1, t1.c3
+                           ->  Foreign Scan on public.ft1 t1
+                                 Output: t1.c1, t1.c3
+                                 Remote SQL: SELECT "C 1", c3 FROM "S 1"."T 1"
+(19 rows)
+
 -- non-Var items in targetlist of the nullable rel of a join preventing
 -- push-down in some cases
 -- unable to push {ft1, ft2}

diff --git a/contrib/postgres_fdw/sql/postgres_fdw.sql b/contrib/postgres_fdw/sql/postgres_fdw.sql
index 5cd1d4b3903210d8d8ec1aa479982d2bd2705fd0..210e79b37e81687be9dbcf44b3d3d8550dff1410 100644 (file)
--- a/contrib/postgres_fdw/sql/postgres_fdw.sql
+++ b/contrib/postgres_fdw/sql/postgres_fdw.sql
@@ -595,6 +595,9 @@ SELECT t1c1, avg(t1c1 + t2c1) FROM (SELECT t1.c1, t2.c1 FROM ft1 t1 JOIN ft2 t2
 EXPLAIN (VERBOSE, COSTS OFF)
 SELECT t1."C 1" FROM "S 1"."T 1" t1, LATERAL (SELECT DISTINCT t2.c1, t3.c1 FROM ft1 t2, ft2 t3 WHERE t2.c1 = t3.c1 AND t2.c2 = t1.c2) q ORDER BY t1."C 1" OFFSET 10 LIMIT 10;
 SELECT t1."C 1" FROM "S 1"."T 1" t1, LATERAL (SELECT DISTINCT t2.c1, t3.c1 FROM ft1 t2, ft2 t3 WHERE t2.c1 = t3.c1 AND t2.c2 = t1.c2) q ORDER BY t1."C 1" OFFSET 10 LIMIT 10;
+-- join with pseudoconstant quals, not pushed down.
+EXPLAIN (VERBOSE, COSTS OFF)
+SELECT t1.c1, t2.c1 FROM ft1 t1 JOIN ft2 t2 ON (t1.c1 = t2.c1 AND CURRENT_USER = SESSION_USER) ORDER BY t1.c3, t1.c1 OFFSET 100 LIMIT 10;
 
 -- non-Var items in targetlist of the nullable rel of a join preventing
 -- push-down in some cases

diff --git a/src/backend/optimizer/path/joinpath.c b/src/backend/optimizer/path/joinpath.c
index 44aa913da2221f16aae39c1716e9ae9e51322bc0..97d4955b8c613f54df7ab7dc6b22fcec7d1da183 100644 (file)
--- a/src/backend/optimizer/path/joinpath.c
+++ b/src/backend/optimizer/path/joinpath.c
@@ -24,6 +24,7 @@
 #include "optimizer/pathnode.h"
 #include "optimizer/paths.h"
 #include "optimizer/planmain.h"
+#include "optimizer/restrictinfo.h"
 #include "utils/typcache.h"
 
 /* Hook for plugins to get control in add_paths_to_joinrel() */
@@ -130,6 +131,7 @@ add_paths_to_joinrel(PlannerInfo *root,
 {
    JoinPathExtraData extra;
    bool        mergejoin_allowed = true;
+   bool        consider_join_pushdown = false;
    ListCell   *lc;
    Relids      joinrelids;
 
@@ -318,13 +320,25 @@ add_paths_to_joinrel(PlannerInfo *root,
        hash_inner_and_outer(root, joinrel, outerrel, innerrel,
                             jointype, &extra);
 
+   /*
+    * createplan.c does not currently support handling of pseudoconstant
+    * clauses assigned to joins pushed down by extensions; check if the
+    * restrictlist has such clauses, and if so, disallow pushing down joins.
+    */
+   if ((joinrel->fdwroutine &&
+        joinrel->fdwroutine->GetForeignJoinPaths) ||
+       set_join_pathlist_hook)
+       consider_join_pushdown = !has_pseudoconstant_clauses(root,
+                                                            restrictlist);
+
    /*
     * 5. If inner and outer relations are foreign tables (or joins) belonging
     * to the same server and assigned to the same user to check access
     * permissions as, give the FDW a chance to push down joins.
     */
    if (joinrel->fdwroutine &&
-       joinrel->fdwroutine->GetForeignJoinPaths)
+       joinrel->fdwroutine->GetForeignJoinPaths &&
+       consider_join_pushdown)
        joinrel->fdwroutine->GetForeignJoinPaths(root, joinrel,
                                                 outerrel, innerrel,
                                                 jointype, &extra);
@@ -332,7 +346,8 @@ add_paths_to_joinrel(PlannerInfo *root,
    /*
     * 6. Finally, give extensions a chance to manipulate the path list.
     */
-   if (set_join_pathlist_hook)
+   if (set_join_pathlist_hook &&
+       consider_join_pushdown)
        set_join_pathlist_hook(root, joinrel, outerrel, innerrel,
                               jointype, &extra);
 }

diff --git a/src/backend/optimizer/util/restrictinfo.c b/src/backend/optimizer/util/restrictinfo.c
index aa9fb3a9fa5e863fb0c0f4ffe307ba82642fa004..2fd29ed30a1dcc2ec8d934e070235bce1fc7ecaa 100644 (file)
--- a/src/backend/optimizer/util/restrictinfo.c
+++ b/src/backend/optimizer/util/restrictinfo.c
@@ -495,6 +495,35 @@ extract_actual_join_clauses(List *restrictinfo_list,
    }
 }
 
+/*
+ * has_pseudoconstant_clauses
+ *
+ * Returns true if 'restrictinfo_list' includes pseudoconstant clauses.
+ *
+ * This is used when we determine whether to allow extensions to consider
+ * pushing down joins in add_paths_to_joinrel().
+ */
+bool
+has_pseudoconstant_clauses(PlannerInfo *root,
+                          List *restrictinfo_list)
+{
+   ListCell   *l;
+
+   /* No need to look if we know there are no pseudoconstants */
+   if (!root->hasPseudoConstantQuals)
+       return false;
+
+   /* See if there are pseudoconstants in the RestrictInfo list */
+   foreach(l, restrictinfo_list)
+   {
+       RestrictInfo *rinfo = lfirst_node(RestrictInfo, l);
+
+       if (rinfo->pseudoconstant)
+           return true;
+   }
+   return false;
+}
+
 
 /*
  * join_clause_is_movable_to

diff --git a/src/include/optimizer/restrictinfo.h b/src/include/optimizer/restrictinfo.h
index 0165ffde37be5d92f039f3d3c5744eb0b04469e9..4ff1d6f1d78f0bf3c0d4f513323c9b8ac6c0a682 100644 (file)
--- a/src/include/optimizer/restrictinfo.h
+++ b/src/include/optimizer/restrictinfo.h
@@ -41,6 +41,8 @@ extern void extract_actual_join_clauses(List *restrictinfo_list,
                                        Relids joinrelids,
                                        List **joinquals,
                                        List **otherquals);
+extern bool has_pseudoconstant_clauses(PlannerInfo *root,
+                                      List *restrictinfo_list);
 extern bool join_clause_is_movable_to(RestrictInfo *rinfo, RelOptInfo *baserel);
 extern bool join_clause_is_movable_into(RestrictInfo *rinfo,
                                        Relids currentrelids,