Re: Some Improvement

>> But I don't see the "Backwards index scan" you mentioned.
> Then we're not there yet.

> I hesitate to suggest that you throw "SET enable_sort TO off" and then
> "SET enable_sort TO on" around your query, because it's so ugly,
> but that might be the best short-term answer.

No, actually that's no short-term answer at all.  It turns out that the
"bogus" cost estimate was perfectly correct, because what the planner
was actually generating was a plan for a backwards index scan over the
whole table, with restrictions applied after the fact :-(.  Forcing it
to use that plan won't help.

I have corrected this silly oversight.  Attached is the patch needed to
make backwards index scans work properly in 7.0.*.
        regards, tom lane

*** src/backend/optimizer/path/indxpath.c.orig    Sun Apr 16 00:41:01 2000
--- src/backend/optimizer/path/indxpath.c    Thu Jul 13 01:49:51 2000
***************
*** 196,202 ****              useful_for_ordering(root, rel, index, ForwardScanDirection))
add_path(rel,(Path *)                          create_index_path(root, rel, index,
 
!                                            NIL,                                            ForwardScanDirection));
    } 
 
--- 196,202 ----              useful_for_ordering(root, rel, index, ForwardScanDirection))
add_path(rel,(Path *)                          create_index_path(root, rel, index,
 
!                                            restrictclauses,
ForwardScanDirection));        } 
 
***************
*** 208,214 ****         if (useful_for_ordering(root, rel, index, BackwardScanDirection))             add_path(rel,
(Path*)                      create_index_path(root, rel, index,
 
!                                        NIL,                                        BackwardScanDirection));
/*
--- 208,214 ----         if (useful_for_ordering(root, rel, index, BackwardScanDirection))             add_path(rel,
(Path*)                      create_index_path(root, rel, index,
 
!                                        restrictclauses,
BackwardScanDirection));         /*