Re: Get more from indices.

Oops! I found a bug in this patch. The previous v8 patch missed
the case that build_index_pathkeys() could build a partial
pathkeys from the index tlist.

This causes the situation follows,

=======
=# \d cu11
Table "public.cu11"
Column | Type | Modifiers
--------+---------+-----------
a | integer | not null
b | integer | not null
c | integer |
d | text |
Indexes:
"cu11_a_b_idx" UNIQUE, btree (a, b)

s=# explain (costs off) select * from cu11 order by a, c ,d;
QUERY PLAN
---------------------------------------
Index Scan using cu11_a_b_idx on cu11
(1 row)
=======

Where the simple ORDER BY a, c, d on the table with index on
columns (a, b) results simple index scan which cannot perform the
order.

The attached v9 patche is fixed by adding a check for the case
into index_pathkeys_are_extensible(), and rebase to current HEAD.

regards,

--
Kyotaro Horiguchi
NTT Open Source Software Center