1 files changed, 31 insertions, 27 deletions

diff --git a/src/backend/optimizer/path/prune.c b/src/backend/optimizer/path/prune.c
index 5b032491600..33fb67bc573 100644
--- a/src/backend/optimizer/path/prune.c
+++ b/src/backend/optimizer/path/prune.c
@@ -7,7 +7,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/optimizer/path/Attic/prune.c,v 1.42 1999/07/16 04:59:16 momjian Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/optimizer/path/Attic/prune.c,v 1.43 1999/08/16 02:17:52 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -18,17 +18,15 @@
 #include "optimizer/pathnode.h"
 #include "optimizer/paths.h"
 
-
-
-static List *merge_rel_with_same_relids(RelOptInfo *rel, Relids unjoined_relids);
+static List *merge_rel_with_same_relids(RelOptInfo *rel, List *unmerged_rels);
 
 /*
  * merge_rels_with_same_relids
  *	  Removes any redundant relation entries from a list of rel nodes
- *	  'rel_list'.  Obviously, the first relation can't be a duplicate.
+ *	  'rel_list', merging their pathlists into the first non-duplicate
+ *	  relation entry for each value of relids.
  *
  * Returns the resulting list.
- *
  */
 void
 merge_rels_with_same_relids(List *rel_list)
@@ -37,17 +35,21 @@ merge_rels_with_same_relids(List *rel_list)
 
 	/*
 	 * rel_list can shorten while running as duplicate relations are
-	 * deleted
+	 * deleted.  Obviously, the first relation can't be a duplicate,
+	 * so the list head pointer won't change.
 	 */
 	foreach(i, rel_list)
-		lnext(i) = merge_rel_with_same_relids((RelOptInfo *) lfirst(i), lnext(i));
+	{
+		lnext(i) = merge_rel_with_same_relids((RelOptInfo *) lfirst(i),
+											  lnext(i));
+	}
 }
 
 /*
  * merge_rel_with_same_relids
- *	  Prunes those relations from 'unjoined_relids' that are redundant with
+ *	  Prunes those relations from 'unmerged_rels' that are redundant with
  *	  'rel'.  A relation is redundant if it is built up of the same
- *	  relations as 'rel'.  Paths for the redundant relation are merged into
+ *	  relations as 'rel'.  Paths for the redundant relations are merged into
  *	  the pathlist of 'rel'.
  *
  * Returns a list of non-redundant relations, and sets the pathlist field
@@ -55,50 +57,52 @@ merge_rels_with_same_relids(List *rel_list)
  *
  */
 static List *
-merge_rel_with_same_relids(RelOptInfo *rel, Relids unjoined_relids)
+merge_rel_with_same_relids(RelOptInfo *rel, List *unmerged_rels)
 {
-	List	   *i = NIL;
 	List	   *result = NIL;
+	List	   *i;
 
-	foreach(i, unjoined_relids)
+	foreach(i, unmerged_rels)
 	{
-		RelOptInfo *unjoined_rel = (RelOptInfo *) lfirst(i);
-
-		if (same(rel->relids, unjoined_rel->relids))
+		RelOptInfo *unmerged_rel = (RelOptInfo *) lfirst(i);
 
+		if (same(rel->relids, unmerged_rel->relids))
+		{
 			/*
-			 * This are on the same relations, so get the best of their
-			 * pathlists.
+			 * These rels are for the same set of base relations,
+			 * so get the best of their pathlists.  We assume it's
+			 * ok to reassign a path to the other RelOptInfo without
+			 * doing more than changing its parent pointer (cf. pathnode.c).
 			 */
 			rel->pathlist = add_pathlist(rel,
 										 rel->pathlist,
-										 unjoined_rel->pathlist);
+										 unmerged_rel->pathlist);
+		}
 		else
-			result = lappend(result, unjoined_rel);
+			result = lappend(result, unmerged_rel);
 	}
 	return result;
 }
 
 /*
  * rels_set_cheapest
- *	  For each relation entry in 'rel_list' (which corresponds to a join
- *	  relation), set pointers to the cheapest path
+ *	  For each relation entry in 'rel_list' (which should contain only join
+ *	  relations), set pointers to the cheapest path and compute rel size.
  */
 void
 rels_set_cheapest(List *rel_list)
 {
-	List	   *x = NIL;
-	RelOptInfo *rel = (RelOptInfo *) NULL;
-	JoinPath   *cheapest;
+	List	   *x;
 
 	foreach(x, rel_list)
 	{
-		rel = (RelOptInfo *) lfirst(x);
+		RelOptInfo	   *rel = (RelOptInfo *) lfirst(x);
+		JoinPath	   *cheapest;
 
 		cheapest = (JoinPath *) set_cheapest(rel, rel->pathlist);
 		if (IsA_JoinPath(cheapest))
 			rel->size = compute_joinrel_size(cheapest);
 		else
-			elog(ERROR, "non JoinPath called");
+			elog(ERROR, "rels_set_cheapest: non JoinPath found");
 	}
 }