properly decide when Grouping Sets do not require redistribution

When adding a GroupingSetsPath, an explicit redistribution is not
needed when either (distribution=NULL) or for replicated tables.
This resolves the crash in 'groupingsets' regression set, due to
triggering this assert in make_remotesubplan():

    Assert(!equal(resultDistribution, execDistribution))

diff --git a/src/backend/optimizer/plan/planner.c b/src/backend/optimizer/plan/planner.c
index 4f98eba64471cc935da880e4bbd2bc20b8bbc25b..1bb2bcb1ce49728953a50ed194d48b07874220be 100644 (file)
--- a/src/backend/optimizer/plan/planner.c
+++ b/src/backend/optimizer/plan/planner.c
@@ -162,6 +162,8 @@ static bool equal_distributions(PlannerInfo *root, Distribution *dst1,
                                        Distribution *dst2);
 static bool grouping_distribution_match(PlannerInfo *root, Query *parse,
                                          Path *path, List *clauses);
+static bool groupingsets_distribution_match(PlannerInfo *root, Query *parse,
+                                         Path *path);
 static Path *adjust_path_distribution(PlannerInfo *root, Query *parse,
                                          Path *path);
 static bool can_push_down_grouping(PlannerInfo *root, Query *parse, Path *path);
@@ -6131,6 +6133,23 @@ grouping_distribution_match(PlannerInfo *root, Query *parse, Path *path,
        return matches_key;
 }
 
+static bool
+groupingsets_distribution_match(PlannerInfo *root, Query *parse, Path *path)
+{
+       Distribution *distribution = path->distribution;
+
+       /*
+        * With no explicit data distribution or replicated tables, we can simply
+        * push down the whole grouping sets to the remote node, without any sort
+        * of redistribution. So consider this to be a match.
+        */
+       if ((distribution == NULL) ||
+               IsLocatorReplicated(distribution->distributionType))
+               return true;
+
+       return false;
+}
+
 /*
  * equal_distributions
  *     Check that two distributions are equal.
@@ -6284,11 +6303,10 @@ static bool
 can_push_down_grouping(PlannerInfo *root, Query *parse, Path *path)
 {
        /* only called when constructing grouping paths */
-       Assert(parse->groupingSets || parse->hasAggs || parse->groupClause);
+       Assert(parse->hasAggs || parse->groupClause);
 
-       /* push-down of grouping sets is not supported yet */
        if (parse->groupingSets)
-               return false;
+               return groupingsets_distribution_match(root, parse, path);
 
        return grouping_distribution_match(root, parse, path, parse->groupClause);
 }