Re: buffer advisor
- From: Ls Cheng <exriscer@xxxxxxxxx>
- To: Chris Taylor <christopherdtaylor1994@xxxxxxxxx>
- Date: Fri, 5 Sep 2014 09:40:41 +0200
Hi Chris
That is why I am still questioning advisr's effciency and asking if people
has got experiences using it to size buffer cache. If we look at ASMM or
AMM which I suppose they use the advisors internally (or no?) the advisor
doesnt seem useful at all.
I just got a couple of AWR from a customer who is using memory_target, set
to 3GB and AMM set shared pool to 2GB, PGA to 900MB and buffer cache to
64MB (!?#!).
Thanks
On Fri, Sep 5, 2014 at 12:50 AM, Chris Taylor <
christopherdtaylor1994@xxxxxxxxx> wrote:
> Seth,
>
> Really? I have run into a few situations where the advisor undersizes
> the buffer cache significantly in favor of the shared pool because of the
> workload of the application.
> I've got a db right _now_ that has a 128MB buffer cache and a 20GB shared
> pool that AMM resized because of the workload :)
>
> Obviously, the solution to this is to set floor (minimum) values for
> shared_pool_size and db_cache_size but it still amazes me that ASMM/AMM
> will significantly undersize the buffer cache when the workload uses a lot
> of SQL that isn't reuseable.
>
> And I clearly recognize that the workload is suboptimal (lots of SQL with
> literals and a few other things) that favor a large shared pool, and my
> only point is that it isn't uncommon for the automatic memory resizing to
> size the buffer cache to an absurd size :)
>
> Chris
>
>
> On Thu, Sep 4, 2014 at 4:56 PM, Seth Miller <sethmiller.sm@xxxxxxxxx>
> wrote:
>
>> Ls,
>>
>> I have found with very few exceptions that ASMM (SGA_TARGET) is very good
>> at sizing the buffer cache. Have you tried this?
>>
>> Seth Miller
>> On Sep 4, 2014 3:38 PM, "Ls Cheng" <exriscer@xxxxxxxxx> wrote:
>>
>>> Hi all
>>>
>>> Has anyone used buffer cache advisory in 10g or 11g to size a production
>>> buffer cache? If so how good is the advisor recommending the cache size?
>>> Did the recommended cache size meet the ohysical reads reduction goal?
>>>
>>> TIA
>>>
>>>
>>>
>
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