*** a/src/backend/optimizer/README
--- b/src/backend/optimizer/README
***************
*** 756,764 **** to create a plan like
          -> Seq Scan on SmallTable1 A
          NestLoop
              -> Seq Scan on SmallTable2 B
!             NestLoop
!                 -> Index Scan using XYIndex on LargeTable C
!                       Index Condition: C.X = A.AID and C.Y = B.BID
  
  so we should be willing to pass down A.AID through a join even though
  there is no join order constraint forcing the plan to look like this.
--- 756,763 ----
          -> Seq Scan on SmallTable1 A
          NestLoop
              -> Seq Scan on SmallTable2 B
!             -> Index Scan using XYIndex on LargeTable C
!                 Index Condition: C.X = A.AID and C.Y = B.BID
  
  so we should be willing to pass down A.AID through a join even though
  there is no join order constraint forcing the plan to look like this.