diff --git a/src/backend/optimizer/path/allpaths.c b/src/backend/optimizer/path/allpaths.c
index e6728f39fe4..c8335868133 100644
--- a/src/backend/optimizer/path/allpaths.c
+++ b/src/backend/optimizer/path/allpaths.c
@@ -8,13 +8,15 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/optimizer/path/allpaths.c,v 1.170 2008/04/01 00:48:33 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/optimizer/path/allpaths.c,v 1.171 2008/06/27 03:56:55 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
 
 #include "postgres.h"
 
+#include <math.h>
+
 #ifdef OPTIMIZER_DEBUG
 #include "nodes/print.h"
 #endif
@@ -263,6 +265,10 @@ set_append_rel_pathlist(PlannerInfo *root, RelOptInfo *rel,
 {
 	int			parentRTindex = rti;
 	List	   *subpaths = NIL;
+	double		parent_rows;
+	double		parent_size;
+	double	   *parent_attrsizes;
+	int			nattrs;
 	ListCell   *l;
 
 	/*
@@ -277,10 +283,23 @@ set_append_rel_pathlist(PlannerInfo *root, RelOptInfo *rel,
 				 errmsg("SELECT FOR UPDATE/SHARE is not supported for inheritance queries")));
 
 	/*
-	 * Initialize to compute size estimates for whole append relation
+	 * Initialize to compute size estimates for whole append relation.
+	 *
+	 * We handle width estimates by weighting the widths of different
+	 * child rels proportionally to their number of rows.  This is sensible
+	 * because the use of width estimates is mainly to compute the total
+	 * relation "footprint" if we have to sort or hash it.  To do this,
+	 * we sum the total equivalent size (in "double" arithmetic) and then
+	 * divide by the total rowcount estimate.  This is done separately for
+	 * the total rel width and each attribute.
+	 *
+	 * Note: if you consider changing this logic, beware that child rels could
+	 * have zero rows and/or width, if they were excluded by constraints.
 	 */
-	rel->rows = 0;
-	rel->width = 0;
+	parent_rows = 0;
+	parent_size = 0;
+	nattrs = rel->max_attr - rel->min_attr + 1;
+	parent_attrsizes = (double *) palloc0(nattrs * sizeof(double));
 
 	/*
 	 * Generate access paths for each member relation, and pick the cheapest
@@ -379,38 +398,53 @@ set_append_rel_pathlist(PlannerInfo *root, RelOptInfo *rel,
 			subpaths = lappend(subpaths, childpath);
 
 		/*
-		 * Propagate size information from the child back to the parent. For
-		 * simplicity, we use the largest widths from any child as the parent
-		 * estimates.  (If you want to change this, beware of child
-		 * attr_widths[] entries that haven't been set and are still 0.)
+		 * Accumulate size information from each child.
 		 */
-		rel->rows += childrel->rows;
-		if (childrel->width > rel->width)
-			rel->width = childrel->width;
-
-		forboth(parentvars, rel->reltargetlist,
-				childvars, childrel->reltargetlist)
+		if (childrel->rows > 0)
 		{
-			Var		   *parentvar = (Var *) lfirst(parentvars);
-			Var		   *childvar = (Var *) lfirst(childvars);
+			parent_rows += childrel->rows;
+			parent_size += childrel->width * childrel->rows;
 
-			if (IsA(parentvar, Var) &&
-				IsA(childvar, Var))
+			forboth(parentvars, rel->reltargetlist,
+					childvars, childrel->reltargetlist)
 			{
-				int			pndx = parentvar->varattno - rel->min_attr;
-				int			cndx = childvar->varattno - childrel->min_attr;
+				Var		   *parentvar = (Var *) lfirst(parentvars);
+				Var		   *childvar = (Var *) lfirst(childvars);
 
-				if (childrel->attr_widths[cndx] > rel->attr_widths[pndx])
-					rel->attr_widths[pndx] = childrel->attr_widths[cndx];
+				if (IsA(parentvar, Var) &&
+					IsA(childvar, Var))
+				{
+					int			pndx = parentvar->varattno - rel->min_attr;
+					int			cndx = childvar->varattno - childrel->min_attr;
+
+					parent_attrsizes[pndx] += childrel->attr_widths[cndx] * childrel->rows;
+				}
 			}
 		}
 	}
 
+	/*
+	 * Save the finished size estimates.
+	 */
+	rel->rows = parent_rows;
+	if (parent_rows > 0)
+	{
+		int		i;
+
+		rel->width = rint(parent_size / parent_rows);
+		for (i = 0; i < nattrs; i++)
+			rel->attr_widths[i] = rint(parent_attrsizes[i] / parent_rows);
+	}
+	else
+		rel->width = 0;			/* attr_widths should be zero already */
+
 	/*
 	 * Set "raw tuples" count equal to "rows" for the appendrel; needed
 	 * because some places assume rel->tuples is valid for any baserel.
 	 */
-	rel->tuples = rel->rows;
+	rel->tuples = parent_rows;
+
+	pfree(parent_attrsizes);
 
 	/*
 	 * Finally, build Append path and install it as the only access path for
diff --git a/src/backend/optimizer/plan/createplan.c b/src/backend/optimizer/plan/createplan.c
index 109a0145475..0884cda6070 100644
--- a/src/backend/optimizer/plan/createplan.c
+++ b/src/backend/optimizer/plan/createplan.c
@@ -10,13 +10,14 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/optimizer/plan/createplan.c,v 1.240 2008/04/17 21:22:14 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/optimizer/plan/createplan.c,v 1.241 2008/06/27 03:56:55 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
 #include "postgres.h"
 
 #include <limits.h>
+#include <math.h>
 
 #include "access/skey.h"
 #include "nodes/makefuncs.h"
@@ -2312,6 +2313,7 @@ make_append(List *appendplans, bool isTarget, List *tlist)
 {
 	Append	   *node = makeNode(Append);
 	Plan	   *plan = &node->plan;
+	double		total_size;
 	ListCell   *subnode;
 
 	/*
@@ -2322,7 +2324,7 @@ make_append(List *appendplans, bool isTarget, List *tlist)
 	plan->startup_cost = 0;
 	plan->total_cost = 0;
 	plan->plan_rows = 0;
-	plan->plan_width = 0;
+	total_size = 0;
 	foreach(subnode, appendplans)
 	{
 		Plan	   *subplan = (Plan *) lfirst(subnode);
@@ -2331,9 +2333,12 @@ make_append(List *appendplans, bool isTarget, List *tlist)
 			plan->startup_cost = subplan->startup_cost;
 		plan->total_cost += subplan->total_cost;
 		plan->plan_rows += subplan->plan_rows;
-		if (plan->plan_width < subplan->plan_width)
-			plan->plan_width = subplan->plan_width;
+		total_size += subplan->plan_width * subplan->plan_rows;
 	}
+	if (plan->plan_rows > 0)
+		plan->plan_width = rint(total_size / plan->plan_rows);
+	else
+		plan->plan_width = 0;
 
 	plan->targetlist = tlist;
 	plan->qual = NIL;