Large number of physical IOs for a simple query

oracle 10.2.0.3
redhat 4.5
table size 160 GB
partition by day
I do:
select count(*)
from mytable
where rownum < 2;
does 122,000 physical reads
I run a 10046 trace and look at tkprof all of my wait time is on the physical reads. It takes 30 seconds to return.
I look at the raw trace file. None of the individual reads seem to take that long. Its just that there are so many of them.
I then take the same query and restrict it by
day field (partitioned field) < a value I dont have in my table
by my assumption this should only scan the first partition. This query has run for 15 minutes and is not returning.
Nothing else is running. The individual physical IO calls are not slow
No problems with any other tables.
This is on a SAN using ASM.

I wonder if the problem is similar to the one in this thread:
http://groups.google.com/group/comp.databases.oracle.server/browse_thread/thread/79d0a3d85381dc64/ed3ab1dbeeaa1cb2
Posts 26-29 arrived at the conclusion that in that particular case the index either needed to be rebuilt or coalesced. The plan showed "INDEX FULL SCAN (MIN/MAX)", which should have only required a very small number of IOs (likely less than 5), but actually required 118,525 logical IOs with 118,248 single block reads from disk.
Charles Hooper
IT Manager/Oracle DBA
K&M Machine-Fabricating, Inc.

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Dear Yogesh,
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log file sync                                   1        0.00          0.00
SQL*Net message to client                       1        0.00          0.00
SQL*Net message from client                     1        0.00          0.00
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Intent
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* Fast invocation even with a large number of pages (which can be the case
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Principle
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Application Server
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I dont know the upper limit, but I think 80 is too much. I have never used more than 15-20. For Nav attributes, a seperate tables are created which causes the Performance issue as result in new join at query run time. Just ask your business guy, if these can be reduced.One way could be to model these attributes as seperate characteristics. It will certainly help.
Thanks...
Shambhu

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