update pathkey description.

src/backend/optimizer/path/pathkeys.c

@@ -7,7 +7,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/optimizer/path/pathkeys.c,v 1.2 1999/02/20 16:28:20 momjian Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/optimizer/path/pathkeys.c,v 1.3 1999/02/20 16:32:35 momjian Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -38,7 +38,7 @@ static List *new_matching_subkeys(Var *subkey, List *considered_subkeys,
 /*
  *	Explanation of Path.pathkeys
  *
- *	This structure is a List of List of Var nodes that represent the sort
+ *	Path.pathkeys is a List of List of Var nodes that represent the sort
  *	order of the result generated by the Path.
  *
  *	In single/base relation RelOptInfo's, the Path's represent various ways
@@ -49,8 +49,8 @@ static List *new_matching_subkeys(Var *subkey, List *considered_subkeys,
  *
  *	Multi-relation RelOptInfo Path's are more complicated.  Mergejoins are
  *	only performed with equajoins("=").  Because of this, the multi-relation
- *	path actually has more than one ordering.  For example, a mergejoin Path
- *	of "tab1.col1 = tab2.col1" would generate a pathkeys of
+ *	path actually has more than one primary Var key.  For example, a
+ *	mergejoin Path of "tab1.col1 = tab2.col1" would generate a pathkeys of
  *	{ {tab1.col1, tab2.col1} }.  This allows future joins to use either Var
  *	as a pre-sorted key to prevent Mergejoins from having to re-sort the Path.
  *	They are equal, so they are both primary sort keys.  This is why pathkeys