BUG #14161: reverse index scan cann't use double link?

The following bug has been logged on the website:

Bug reference: 14161
Logged by: Zhou Digoal
Email address: digoal(at)126(dot)com
PostgreSQL version: 9.6beta1
Operating system: CentOS 6.x x64
Description:

HI,
in btree, leaf page has prev and next page. but when i use order by desc,
it's not use the prev page link? it scan from root per leaf page.

9 page hint = meta + root + branch + 6 leaf
19 page hint = meta + 6(root + branch + leaf)

postgres=# explain (analyze,verbose,timing,costs,buffers) select id from
tbl1 order by id limit 1000;
QUERY PLAN

-----------------------------------------------------------------------------------------------------------------------------------------------
Limit (cost=0.43..19.05 rows=1000 width=4) (actual time=0.027..0.714
rows=1000 loops=1)
Output: id
Buffers: shared hit=9
-> Index Only Scan using tbl1_pkey on public.tbl1 (cost=0.43..73252.49
rows=3934871 width=4) (actual time=0.025..0.298 rows=1000 loops=1)
Output: id
Heap Fetches: 0
Buffers: shared hit=9
Planning time: 0.081 ms
Execution time: 0.908 ms
(9 rows)

postgres=# explain (analyze,verbose,timing,costs,buffers) select id from
tbl1 order by id desc limit 1000;
QUERY
PLAN

--------------------------------------------------------------------------------------------------------------------------------------------------------
Limit (cost=0.43..19.05 rows=1000 width=4) (actual time=0.030..0.665
rows=1000 loops=1)
Output: id
Buffers: shared hit=19
-> Index Only Scan Backward using tbl1_pkey on public.tbl1
(cost=0.43..73252.49 rows=3934871 width=4) (actual time=0.029..0.303
rows=1000 loops=1)
Output: id
Heap Fetches: 0
Buffers: shared hit=19
Planning time: 0.106 ms
Execution time: 0.860 ms
(9 rows)

best regards
digoal