db buffer cache advisory clarification

Can anyone let me know why the advisory is saying i can so drastically
reduce my PIO's by reducing my db_cache_size? I have looked around the web
and have never seen an explanation for this.  I also looked on metalink to
see if it was a know bug.

This was from a lvl 5 statspack 15 minute snap on 9.2.0.3 on Sun Solaris.
The instance has been up for over 8 months.  The results are the same no
matter when I snap.

Buffer Pool Advisory for DB: MERLIN  Instance: MERLIN  End Snap: 15
-> Only rows with estimated physical reads >0 are displayed
-> ordered by Block Size, Buffers For Estimate

        Size for  Size      Buffers for  Est Physical          Estimated
P   Estimate (M) Factr         Estimate   Read Factor     Physical Reads
--- ------------ ----- ---------------- ------------- ------------------
D             16    .3            1,985          0.06         54,232,173
D             32    .5            3,970          0.03         28,255,991
D             48    .8            5,955          0.01          7,094,145
D             64   1.0            7,940          1.00        937,436,311
D             80   1.3            9,925          0.99        924,356,448
D             96   1.5           11,910          0.97        912,150,561
...
D            272   4.3           33,745          0.85        792,237,723
D            288   4.5           35,730          0.84        783,014,854
D            304   4.8           37,715          0.82        769,676,998
D            320   5.0           39,700          0.79        738,539,663
          -------------------------------------------------------------

Regards,
Steve Anderson

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