Re: db buffer cache advisory clarification

Steve:

I am seeing it other way around. PIO is getting reduced with increased estimate size. Below detail from a production statspack report. We recycle the DB during weekend..

Jay

Buffer Pool Advisory for DB: WDSP Instance: WDSP End Snap: 4040 -> 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             32    .1            3,970         33.20      1,601,419,883
D             64    .2            7,940         23.86      1,150,897,477
D             96    .3           11,910         15.87        765,448,716
D            128    .4           15,880          1.61         77,887,469
D            160    .5           19,850          1.33         63,917,781
D            192    .5           23,820          1.20         58,065,691
D            224    .6           27,790          1.13         54,488,453
D            256    .7           31,760          1.08         52,177,905
D            288    .8           35,730          1.05         50,519,436
D            320    .9           39,700          1.02         49,257,170
D            352   1.0           43,670          1.00         48,240,061
D            384   1.1           47,640          0.98         47,376,752
D            416   1.2           51,610          0.97         46,571,856
D            448   1.3           55,580          0.95         45,897,062
D            480   1.4           59,550          0.94         45,287,072
D            512   1.5           63,520          0.93         44,733,134
D            544   1.5           67,490          0.92         44,206,534
D            576   1.6           71,460          0.91         43,725,760
D            608   1.7           75,430          0.90         43,284,321
D            640   1.8           79,400          0.89         42,853,995
          -------------------------------------------------------------

On 3/28/06, Stephen Anderson <st.anderson_at_gmail.com> wrote:
>
> 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
>

--
http://www.freelists.org/webpage/oracle-l