Improve some comments.

src/include/nodes/relation.h

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2002, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $Id: relation.h,v 1.69 2002/11/24 21:52:15 tgl Exp $
+ * $Id: relation.h,v 1.70 2002/11/27 20:52:04 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -171,7 +171,7 @@ typedef struct RelOptInfo
 	RelOptKind	reloptkind;
 
 	/* all relations included in this RelOptInfo */
-	Relids		relids;			/* integer list of base relids (RT
+	Relids		relids;			/* integer list of base relids (rangetable
 								 * indexes) */
 
 	/* size estimates generated by planner */
@@ -304,6 +304,11 @@ typedef struct PathKeyItem
 /*
  * Type "Path" is used as-is for sequential-scan paths.  For other
  * path types it is the first component of a larger struct.
+ *
+ * Note: "pathtype" is the NodeTag of the Plan node we could build from this
+ * Path.  It is partially redundant with the Path's NodeTag, but allows us
+ * to use the same Path type for multiple Plan types where there is no need
+ * to distinguish the Plan type during path processing.
  */
 
 typedef struct Path
@@ -319,7 +324,6 @@ typedef struct Path
 								 * fetched) */
 
 	NodeTag		pathtype;		/* tag identifying scan/join method */
-	/* XXX why is pathtype separate from the NodeTag? */
 
 	List	   *pathkeys;		/* sort ordering of path's output */
 	/* pathkeys is a List of Lists of PathKeyItem nodes; see above */
@@ -373,7 +377,7 @@ typedef struct IndexPath
 typedef struct TidPath
 {
 	Path		path;
-	List	   *tideval;
+	List	   *tideval;			/* qual(s) involving CTID = something */
 	Relids		unjoined_relids;	/* some rels not yet part of my Path */
 } TidPath;