Re: Average physical read times
- From: "John Kanagaraj" <john.kanagaraj@xxxxxxxxx>
- To: andrew.kerber@xxxxxxxxx, daniel.fink@xxxxxxxxxxxxxx, oracle-l <oracle-l@xxxxxxxxxxxxx>
- Date: Wed, 24 Sep 2008 18:26:28 -0700
Hi Dan,
The good prod systems give me 2-3 ms and 10 ms is an outlier. Since
you are on 10g, have a look at the snapshots of file i/o histograms.
You will need 10g statspack - awr does not record this. Look at my
collab 08 paper for more info on how to get this.
One issue I have seen on test systems is the small number of large
disks that, when combined with a small san cache can quickly be
overwhelmed, and the equivalent of latching on the san cache
contributing to this.
Also consider the fact that a cpu-loaded db server could artificially
inflate disk wait times.
John
On 9/24/08, Andrew Kerber <andrew.kerber@xxxxxxxxx> wrote:
> That is rarely above 10ms.
>
> On Wed, Sep 24, 2008 at 12:50 PM, Andrew Kerber
> <andrew.kerber@xxxxxxxxx>wrote:
>
>> I have seen as small as 2 ms, rarely about 10 ms. Did you check and see
>> if
>> the DBFMBRC might be set too high?
>>
>>
>> On Wed, Sep 24, 2008 at 11:17 AM, Daniel Fink
>> <daniel.fink@xxxxxxxxxxxxxx>wrote:
>>
>>> In a recent optimization effort, I found what I think are high physical
>>> read times. For example, a single block read was averaging 11
>>> milliseconds
>>> with a max of over 1 second (tkprof output). For this session, single
>>> block
>>> reads consumed over 80% of the response time, so this is of concern.
>>>
>>> We are running Oracle 10gr1 on AIX with an IBM storage array (shared
>>> amongst many servers). I suspect there is some optimization that can be
>>> done
>>> at the storage array level. If 11 milliseconds is well above average,
>>> this
>>> will help in engaging that team in the process.
>>>
>>> For those of you running statspack. AWR or other monitoring tools, what
>>> are the average single block read times you are encountering on a good
>>> system? If you are running on an IBM storage array, have you found any
>>> specific issues/fixes?
>>>
>>> Regards,
>>> Daniel Fink
>>>
>>> --
>>> Daniel Fink
>>>
>>> OptimalDBA.com - Oracle Performance, Diagnosis, Data Recovery and
>>> Training
>>>
>>> OptimalDBA http://www.optimaldba.com
>>> Oracle Blog http://optimaldba.blogspot.com
>>>
>>> Lost Data? http://www.ora600.be/
>>>
>>> --
>>> //www.freelists.org/webpage/oracle-l
>>>
>>>
>>>
>>
>>
>> --
>> Andrew W. Kerber
>>
>> 'If at first you dont succeed, dont take up skydiving.'
>>
>
>
>
> --
> Andrew W. Kerber
>
> 'If at first you dont succeed, dont take up skydiving.'
>
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