Re: High mbrc in aux_stats$

On 03/10/2006 06:44:25 PM, Allen, Brandon wrote:
> Anybody seen this before?
> 
>
> Notice the MBRC figure of 97 even though I have 
> db_file_multiblock_read_count=16.  I searched Metalink for bugs and known 
> issues but no luck.  I guess the next step is to peform a 10046 trace and 
> check the p3 value for all the 'db file scattered reads', but I figured I'd 
> check to see if any of you have already seen this before I go to that trouble.
> 
> Thanks,
> Brandon



Brandon, this setting IS trouble. Oracle will use DB_MULTIBLOCK_READ_COUNT 
batches but CBO
will set the price for full table scan as if it was possible to read 97 blocks 
at once. Price
of full table scan will be very low, lower then the price of a second hand Kia 
at your local 
Kia sales event, which means that you will have a lot of them. CBO will not 
consider index
path as a viable path, which is great if the only things you're running are 
reports from a DW
or a data mart. If, on the other hand, the database in question is an OLTP 
database, then I,
as a foreigner who speaks poor English, cannot describe the situation without 
using the f-word.
I doubt that Steve Adams would have enough undersanding to allow me that 
liberty.

-- 
Mladen Gogala
http://www.mgogala.com

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

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