reverse key index -- Sorting expected?

consider the following case:
create table randomload(roll number, name varchar2(20), mark1 number); populate the table with randomdata.
create index roll_desc_idx on randomload(roll desc); or even ascending index...
roll is a unique key monotonically increasing.

so if the maximum value is 1000000 - this value is stored in the left most leaf block in the index btree structure.

Now consider the following situation:
select * from students where student_id in (1,100000, 200000, 300000, 400000);
we can use the above values in any order we want, here is precisely what oracle is doing even before the final query transformation is done, it eliminates the duplicate values and sorts the values in the ascending order. the query after final transformation becomes.. select * from students where student_id =1 or student_id = 100000 or student_id=200000 or student_id = 300000 or student_id = 400000;

this works precisely as expected for all normal indexes and descending indexes, since sorting them in ascending order as oracle can minimize the IO if the values are adjacent to each other. but works horrible for reverse key indexes.... as there is no order to which the oracle scans the leaf blocks.

I mean by default Oracle sorts these values in ascending order regardless of what, for the descending index: there is no issue with the descending indexes as well (but not in all the cases) ... but for reverse key indexes?

trace of index leaf block reads for a descending index...

WAIT #140268739421912: nam='db file sequential read' ela= 90 file#=7
block#=30099 blocks=1 obj#=74642 tim=5089544852
WAIT #140268739421912: nam='db file sequential read' ela= 95 file#=7
block#=29904 blocks=1 obj#=74642 tim=5089545009
WAIT #140268739421912: nam='db file sequential read' ela= 83 file#=7
block#=29667 blocks=1 obj#=74642 tim=5089545184
WAIT #140268739421912: nam='db file sequential read' ela= 101 file#=7
block#=29430 blocks=1 obj#=74642 tim=5089545354
WAIT #140268739421912: nam='db file scattered read' ela= 199 file#=7
block#=29424 blocks=6 obj#=74642 tim=5089545650
WAIT #140268739421912: nam='db file sequential read' ela= 86 file#=7
block#=29192 blocks=1 obj#=74642 tim=5089545807

WAIT #140452225803960: nam='db file sequential read' ela= 215 file#=7
block#=17470 blocks=1 obj#=74643 tim=5897433740
WAIT #140452225803960: nam='db file sequential read' ela= 213 file#=7
block#=16909 blocks=1 obj#=74643 tim=5897434021

WAIT #140452225803960: nam='db file sequential read' ela= 228 file#=7
block#=18162 blocks=1 obj#=74643 tim=5897434785
WAIT #140452225803960: nam='db file sequential read' ela= 221 file#=7
block#=18080 blocks=1 obj#=74643 tim=5897435085
WAIT #140452225803960: nam='SQL*Net message to client' ela= 1 driver

WAIT #140452225803960: nam='db file sequential read' ela= 214 file#=7
block#=19545 blocks=1 obj#=74643 tim=5897435399
WAIT #140452225803960: nam='db file sequential read' ela= 213 file#=7
block#=19383 blocks=1 obj#=74643 tim=5897435681
WAIT #140452225803960: nam='db file sequential read' ela= 209 file#=7
block#=20929 blocks=1 obj#=74643 tim=5897435960
WAIT #140452225803960: nam='db file sequential read' ela= 192 file#=7
block#=20686 blocks=1 obj#=74643 tim=5897436213
WAIT #140452225803960: nam='db file sequential read' ela= 183 file#=7
block#=22313 blocks=1 obj#=74643 tim=5897436471
WAIT #140452225803960: nam='db file sequential read' ela= 202 file#=7
block#=21989 blocks=1 obj#=74643 tim=5897436735
WAIT #140452225803960: nam='db file sequential read' ela= 223 file#=7
block#=23696 blocks=1 obj#=74643 tim=5897437039
WAIT #140452225803960: nam='db file sequential read' ela= 207 file#=7
block#=23292 blocks=1 obj#=74643 tim=5897437320

Is this a bug? from what I look at applying a hash function to eliminate the duplicates and sorting the results especially for reverse key indexes is basically an unnecessary step....

Thanks,
Vishnu

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