Fix bogus handling of JOIN_UNIQUE_OUTER/INNER cases for parallel joins.

consider_parallel_nestloop passed the wrong jointype down to its
subroutines for JOIN_UNIQUE_INNER cases (it should pass JOIN_INNER), and it
thought that it could pass paths other than innerrel->cheapest_total_path
to create_unique_path, which create_unique_path is not on board with.
These bugs would lead to assertion failures or other errors, suggesting
that this code path hasn't been tested much.

hash_inner_and_outer's code for parallel join effectively treated both
JOIN_UNIQUE_OUTER and JOIN_UNIQUE_INNER the same as JOIN_INNER (for
different reasons :-(), leading to incorrect plans that treated a semijoin
as if it were a plain join.

Michael Day submitted a test case demonstrating that hash_inner_and_outer
failed for JOIN_UNIQUE_OUTER, and I found the other cases through code
review.

Report: https://postgr.es/m/D0E8A029-D1AC-42E8-979A-5DE4A77E4413@rcmail.com

diff --git a/src/backend/optimizer/path/joinpath.c b/src/backend/optimizer/path/joinpath.c
index e47189a339d14c456192b0bc6eef4e71072df6e7..96f00fca5bf5cc9315b18d639cd82fe35e5e120c 100644 (file)
--- a/src/backend/optimizer/path/joinpath.c
+++ b/src/backend/optimizer/path/joinpath.c
@@ -1217,8 +1217,12 @@ consider_parallel_nestloop(PlannerInfo *root,
                           JoinType jointype,
                           JoinPathExtraData *extra)
 {
+   JoinType    save_jointype = jointype;
    ListCell   *lc1;
 
+   if (jointype == JOIN_UNIQUE_INNER)
+       jointype = JOIN_INNER;
+
    foreach(lc1, outerrel->partial_pathlist)
    {
        Path       *outerpath = (Path *) lfirst(lc1);
@@ -1244,18 +1248,19 @@ consider_parallel_nestloop(PlannerInfo *root,
                continue;
 
            /*
-            * Like match_unsorted_outer, we only consider a single nestloop
-            * path when the jointype is JOIN_UNIQUE_INNER.  But we have to
-            * scan cheapest_parameterized_paths to find the one we want to
-            * consider, because cheapest_total_path might not be
-            * parallel-safe.
+            * If we're doing JOIN_UNIQUE_INNER, we can only use the inner's
+            * cheapest_total_path, and we have to unique-ify it.  (We might
+            * be able to relax this to allow other safe, unparameterized
+            * inner paths, but right now create_unique_path is not on board
+            * with that.)
             */
-           if (jointype == JOIN_UNIQUE_INNER)
+           if (save_jointype == JOIN_UNIQUE_INNER)
            {
-               if (!bms_is_empty(PATH_REQ_OUTER(innerpath)))
+               if (innerpath != innerrel->cheapest_total_path)
                    continue;
                innerpath = (Path *) create_unique_path(root, innerrel,
-                                                  innerpath, extra->sjinfo);
+                                                       innerpath,
+                                                       extra->sjinfo);
                Assert(innerpath);
            }
 
@@ -1284,6 +1289,7 @@ hash_inner_and_outer(PlannerInfo *root,
                     JoinType jointype,
                     JoinPathExtraData *extra)
 {
+   JoinType    save_jointype = jointype;
    bool        isouterjoin = IS_OUTER_JOIN(jointype);
    List       *hashclauses;
    ListCell   *l;
@@ -1450,9 +1456,9 @@ hash_inner_and_outer(PlannerInfo *root,
         * extended rows.  Also, the resulting path must not be parameterized.
         */
        if (joinrel->consider_parallel &&
-           jointype != JOIN_UNIQUE_OUTER &&
-           jointype != JOIN_FULL &&
-           jointype != JOIN_RIGHT &&
+           save_jointype != JOIN_UNIQUE_OUTER &&
+           save_jointype != JOIN_FULL &&
+           save_jointype != JOIN_RIGHT &&
            outerrel->partial_pathlist != NIL &&
            bms_is_empty(joinrel->lateral_relids))
        {
@@ -1466,11 +1472,12 @@ hash_inner_and_outer(PlannerInfo *root,
             * Normally, given that the joinrel is parallel-safe, the cheapest
             * total inner path will also be parallel-safe, but if not, we'll
             * have to search cheapest_parameterized_paths for the cheapest
-            * unparameterized inner path.
+            * safe, unparameterized inner path.  If doing JOIN_UNIQUE_INNER,
+            * we can't use any alternative inner path.
             */
            if (cheapest_total_inner->parallel_safe)
                cheapest_safe_inner = cheapest_total_inner;
-           else
+           else if (save_jointype != JOIN_UNIQUE_INNER)
            {
                ListCell   *lc;