Revise make_partition_pruneinfo to not use its partitioned_rels input.

It turns out that the calculation of [Merge]AppendPath.partitioned_rels
in allpaths.c is faulty and sometimes omits relevant non-leaf partitions,
allowing an assertion added by commit a929e17e5a to trigger.  Rather
than fix that, it seems better to get rid of those fields altogether.
We don't really need the info until create_plan time, and calculating
it once for the selected plan should be cheaper than calculating it
for each append path we consider.

As a first step, teach make_partition_pruneinfo to collect the relevant
partitioned tables for itself.  It's not hard to do so by traversing
from child tables up to parents using the AppendRelInfo links.

While here, make some minor stylistic improvements; mainly, don't use
the "Relids" alias for bitmapsets that are not identities of any
relation considered by the planner.  Try to document the logic better,
too.

No backpatch, as there does not seem to be a live problem before
a929e17e5a.  Also no new regression test; the code where the bug
was will be gone at the end of this patch series, so it seems a
bit pointless to memorialize the issue.

Tom Lane and David Rowley, per reports from Andreas Seltenreich
and Jaime Casanova.

Discussion: https://postgr.es/m/87sg8tqhsl.fsf@aurora.ydns.eu
Discussion: https://postgr.es/m/CAJKUy5gCXDSmFs2c=R+VGgn7FiYcLCsEFEuDNNLGfoha=pBE_g@mail.gmail.com

src/backend/partitioning/partprune.c

@@ -138,10 +138,12 @@ typedef struct PruneStepResult
 } PruneStepResult;
 
 
+static List *add_part_relids(List *allpartrelids, Bitmapset *partrelids);
 static List *make_partitionedrel_pruneinfo(PlannerInfo *root,
 										   RelOptInfo *parentrel,
+										   List *prunequal,
+										   Bitmapset *partrelids,
 										   int *relid_subplan_map,
-										   Relids partrelids, List *prunequal,
 										   Bitmapset **matchedsubplans);
 static void gen_partprune_steps(RelOptInfo *rel, List *clauses,
 								PartClauseTarget target,
@@ -213,67 +215,105 @@ static void partkey_datum_from_expr(PartitionPruneContext *context,
  *
  * 'parentrel' is the RelOptInfo for an appendrel, and 'subpaths' is the list
  * of scan paths for its child rels.
- *
- * 'partitioned_rels' is a List containing Lists of relids of partitioned
- * tables (a/k/a non-leaf partitions) that are parents of some of the child
- * rels.  Here we attempt to populate the PartitionPruneInfo by adding a
- * 'prune_infos' item for each sublist in the 'partitioned_rels' list.
- * However, some of the sets of partitioned relations may not require any
- * run-time pruning.  In these cases we'll simply not include a 'prune_infos'
- * item for that set and instead we'll add all the subplans which belong to
- * that set into the PartitionPruneInfo's 'other_subplans' field.  Callers
- * will likely never want to prune subplans which are mentioned in this field.
- *
- * 'prunequal' is a list of potential pruning quals.
+ * 'prunequal' is a list of potential pruning quals (i.e., restriction
+ * clauses that are applicable to the appendrel).
  */
 PartitionPruneInfo *
 make_partition_pruneinfo(PlannerInfo *root, RelOptInfo *parentrel,
-						 List *subpaths, List *partitioned_rels,
+						 List *subpaths, List *unused_partitioned_rels,
 						 List *prunequal)
 {
 	PartitionPruneInfo *pruneinfo;
 	Bitmapset  *allmatchedsubplans = NULL;
+	List	   *allpartrelids;
+	List	   *prunerelinfos;
 	int		   *relid_subplan_map;
 	ListCell   *lc;
-	List	   *prunerelinfos;
 	int			i;
 
 	/*
-	 * Construct a temporary array to map from planner relids to subplan
-	 * indexes.  For convenience, we use 1-based indexes here, so that zero
-	 * can represent an un-filled array entry.
+	 * Scan the subpaths to see which ones are scans of partition child
+	 * relations, and identify their parent partitioned rels.  (Note: we must
+	 * restrict the parent partitioned rels to be parentrel or children of
+	 * parentrel, otherwise we couldn't translate prunequal to match.)
+	 *
+	 * Also construct a temporary array to map from partition-child-relation
+	 * relid to the index in 'subpaths' of the scan plan for that partition.
+	 * (Use of "subplan" rather than "subpath" is a bit of a misnomer, but
+	 * we'll let it stand.)  For convenience, we use 1-based indexes here, so
+	 * that zero can represent an un-filled array entry.
 	 */
+	allpartrelids = NIL;
 	relid_subplan_map = palloc0(sizeof(int) * root->simple_rel_array_size);
 
-	/*
-	 * relid_subplan_map maps relid of a leaf partition to the index in
-	 * 'subpaths' of the scan plan for that partition.
-	 */
 	i = 1;
 	foreach(lc, subpaths)
 	{
 		Path	   *path = (Path *) lfirst(lc);
 		RelOptInfo *pathrel = path->parent;
 
-		Assert(IS_SIMPLE_REL(pathrel));
-		Assert(pathrel->relid < root->simple_rel_array_size);
-		/* No duplicates please */
-		Assert(relid_subplan_map[pathrel->relid] == 0);
+		/* We don't consider partitioned joins here */
+		if (pathrel->reloptkind == RELOPT_OTHER_MEMBER_REL)
+		{
+			RelOptInfo *prel = pathrel;
+			Bitmapset  *partrelids = NULL;
 
-		relid_subplan_map[pathrel->relid] = i++;
+			/*
+			 * Traverse up to the pathrel's topmost partitioned parent,
+			 * collecting parent relids as we go; but stop if we reach
+			 * parentrel.  (Normally, a pathrel's topmost partitioned parent
+			 * is either parentrel or a UNION ALL appendrel child of
+			 * parentrel.  But when handling partitionwise joins of
+			 * multi-level partitioning trees, we can see an append path whose
+			 * parentrel is an intermediate partitioned table.)
+			 */
+			do
+			{
+				AppendRelInfo *appinfo;
+
+				Assert(prel->relid < root->simple_rel_array_size);
+				appinfo = root->append_rel_array[prel->relid];
+				prel = find_base_rel(root, appinfo->parent_relid);
+				if (!IS_PARTITIONED_REL(prel))
+					break;		/* reached a non-partitioned parent */
+				/* accept this level as an interesting parent */
+				partrelids = bms_add_member(partrelids, prel->relid);
+				if (prel == parentrel)
+					break;		/* don't traverse above parentrel */
+			} while (prel->reloptkind == RELOPT_OTHER_MEMBER_REL);
+
+			if (partrelids)
+			{
+				/*
+				 * Found some relevant parent partitions, which may or may not
+				 * overlap with partition trees we already found.  Add new
+				 * information to the allpartrelids list.
+				 */
+				allpartrelids = add_part_relids(allpartrelids, partrelids);
+				/* Also record the subplan in relid_subplan_map[] */
+				/* No duplicates please */
+				Assert(relid_subplan_map[pathrel->relid] == 0);
+				relid_subplan_map[pathrel->relid] = i;
+			}
+		}
+		i++;
 	}
 
-	/* We now build a PartitionedRelPruneInfo for each partitioned rel. */
+	/*
+	 * We now build a PartitionedRelPruneInfo for each topmost partitioned rel
+	 * (omitting any that turn out not to have useful pruning quals).
+	 */
 	prunerelinfos = NIL;
-	foreach(lc, partitioned_rels)
+	foreach(lc, allpartrelids)
 	{
-		Relids		partrelids = (Relids) lfirst(lc);
+		Bitmapset  *partrelids = (Bitmapset *) lfirst(lc);
 		List	   *pinfolist;
 		Bitmapset  *matchedsubplans = NULL;
 
 		pinfolist = make_partitionedrel_pruneinfo(root, parentrel,
+												  prunequal,
+												  partrelids,
 												  relid_subplan_map,
-												  partrelids, prunequal,
 												  &matchedsubplans);
 
 		/* When pruning is possible, record the matched subplans */
@@ -299,7 +339,7 @@ make_partition_pruneinfo(PlannerInfo *root, RelOptInfo *parentrel,
 	pruneinfo->prune_infos = prunerelinfos;
 
 	/*
-	 * Some subplans may not belong to any of the listed partitioned rels.
+	 * Some subplans may not belong to any of the identified partitioned rels.
 	 * This can happen for UNION ALL queries which include a non-partitioned
 	 * table, or when some of the hierarchies aren't run-time prunable.  Build
 	 * a bitmapset of the indexes of all such subplans, so that the executor
@@ -321,28 +361,86 @@ make_partition_pruneinfo(PlannerInfo *root, RelOptInfo *parentrel,
 	return pruneinfo;
 }
 
+/*
+ * add_part_relids
+ *		Add new info to a list of Bitmapsets of partitioned relids.
+ *
+ * Within 'allpartrelids', there is one Bitmapset for each topmost parent
+ * partitioned rel.  Each Bitmapset contains the RT indexes of the topmost
+ * parent as well as its relevant non-leaf child partitions.  Since (by
+ * construction of the rangetable list) parent partitions must have lower
+ * RT indexes than their children, we can distinguish the topmost parent
+ * as being the lowest set bit in the Bitmapset.
+ *
+ * 'partrelids' contains the RT indexes of a parent partitioned rel, and
+ * possibly some non-leaf children, that are newly identified as parents of
+ * some subpath rel passed to make_partition_pruneinfo().  These are added
+ * to an appropriate member of 'allpartrelids'.
+ *
+ * Note that the list contains only RT indexes of partitioned tables that
+ * are parents of some scan-level relation appearing in the 'subpaths' that
+ * make_partition_pruneinfo() is dealing with.  Also, "topmost" parents are
+ * not allowed to be higher than the 'parentrel' associated with the append
+ * path.  In this way, we avoid expending cycles on partitioned rels that
+ * can't contribute useful pruning information for the problem at hand.
+ * (It is possible for 'parentrel' to be a child partitioned table, and it
+ * is also possible for scan-level relations to be child partitioned tables
+ * rather than leaf partitions.  Hence we must construct this relation set
+ * with reference to the particular append path we're dealing with, rather
+ * than looking at the full partitioning structure represented in the
+ * RelOptInfos.)
+ */
+static List *
+add_part_relids(List *allpartrelids, Bitmapset *partrelids)
+{
+	Index		targetpart;
+	ListCell   *lc;
+
+	/* We can easily get the lowest set bit this way: */
+	targetpart = bms_next_member(partrelids, -1);
+	Assert(targetpart > 0);
+
+	/* Look for a matching topmost parent */
+	foreach(lc, allpartrelids)
+	{
+		Bitmapset  *currpartrelids = (Bitmapset *) lfirst(lc);
+		Index		currtarget = bms_next_member(currpartrelids, -1);
+
+		if (targetpart == currtarget)
+		{
+			/* Found a match, so add any new RT indexes to this hierarchy */
+			currpartrelids = bms_add_members(currpartrelids, partrelids);
+			lfirst(lc) = currpartrelids;
+			return allpartrelids;
+		}
+	}
+	/* No match, so add the new partition hierarchy to the list */
+	return lappend(allpartrelids, partrelids);
+}
+
 /*
  * make_partitionedrel_pruneinfo
- *		Build a List of PartitionedRelPruneInfos, one for each partitioned
- *		rel.  These can be used in the executor to allow additional partition
- *		pruning to take place.
- *
- * Here we generate partition pruning steps for 'prunequal' and also build a
- * data structure which allows mapping of partition indexes into 'subpaths'
- * indexes.
- *
- * If no non-Const expressions are being compared to the partition key in any
- * of the 'partitioned_rels', then we return NIL to indicate no run-time
- * pruning should be performed.  Run-time pruning would be useless since the
- * pruning done during planning will have pruned everything that can be.
- *
- * On non-NIL return, 'matchedsubplans' is set to the subplan indexes which
- * were matched to this partition hierarchy.
+ *		Build a List of PartitionedRelPruneInfos, one for each interesting
+ *		partitioned rel in a partitioning hierarchy.  These can be used in the
+ *		executor to allow additional partition pruning to take place.
+ *
+ * parentrel: rel associated with the appendpath being considered
+ * prunequal: potential pruning quals, represented for parentrel
+ * partrelids: Set of RT indexes identifying relevant partitioned tables
+ *   within a single partitioning hierarchy
+ * relid_subplan_map[]: maps child relation relids to subplan indexes
+ * matchedsubplans: on success, receives the set of subplan indexes which
+ *   were matched to this partition hierarchy
+ *
+ * If we cannot find any useful run-time pruning steps, return NIL.
+ * However, on success, each rel identified in partrelids will have
+ * an element in the result list, even if some of them are useless.
  */
 static List *
 make_partitionedrel_pruneinfo(PlannerInfo *root, RelOptInfo *parentrel,
+							  List *prunequal,
+							  Bitmapset *partrelids,
 							  int *relid_subplan_map,
-							  Relids partrelids, List *prunequal,
 							  Bitmapset **matchedsubplans)
 {
 	RelOptInfo *targetpart = NULL;
@@ -2421,11 +2519,12 @@ get_steps_using_prefix_recurse(GeneratePruningStepsContext *context,
 		 */
 		Assert(list_length(step_exprs) == cur_keyno ||
 			   !bms_is_empty(step_nullkeys));
+
 		/*
 		 * Note also that for hash partitioning, each partition key should
 		 * have either equality clauses or an IS NULL clause, so if a
-		 * partition key doesn't have an expression, it would be specified
-		 * in step_nullkeys.
+		 * partition key doesn't have an expression, it would be specified in
+		 * step_nullkeys.
 		 */
 		Assert(context->rel->part_scheme->strategy
 			   != PARTITION_STRATEGY_HASH ||