Re: High mbrc in aux_stats$
- From: Mladen Gogala <gogala@xxxxxxxxxxxxx>
- To: Brandon.Allen@xxxxxxxxxxx
- Date: Fri, 10 Mar 2006 19:45:09 -0500
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
--
//www.freelists.org/webpage/oracle-l
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