Re: Is my Oracle Server issuing more IO than it can handle
- From: Harel Safra <harel.safra@xxxxxxxxx>
- To: Cary Millsap <cary.millsap@xxxxxxxxxxxx>
- Date: Wed, 8 Dec 2010 22:32:54 +0200
I queried it from the ASM instance. Delta read time / Delta reads over a few
minutes. I didn't correlate against other metrics but the times seem
reliable.
Harel Safra
Sent from my phone
On Dec 8, 2010 7:46 PM, "Cary Millsap" <cary.millsap@xxxxxxxxxxxx> wrote:
> Is the AVG_WRITE_TIME statistic actually reliable? I think it's probably
> not—at least it wasn't some time in the past, if you were using async I/O.
>
> Cary Millsap
> Method R Corporation
> http://method-r.com
>
>
> On Wed, Dec 8, 2010 at 11:41 AM, Harel Safra <harel.safra@xxxxxxxxx>
wrote:
>
>> On 08/12/2010 17:13, Amaral, Rui wrote:
>>
>> Yes in theory that can be true but it depends on several factors:
>>
>>
>> Why in theory? Please have a look at a snapshot of statistics from one
>> node of our data warehouse cluster running on EMC DMX4 storage:
>> *AVG_WRITE_TIME* *TOTAL_WRITES* *AVG_READ_TIME* *TOTAL_READS* 1.1 40460
>> 26.78 35864
>> Much better write times than read times (the high read time is also
>> contributed from the large IO the database tends to do).
>>
>> 1) assuming write-back caches on the array have not been disabled (which
in my opinion they should be)
>>
>> Why do you think write back cache should be disabled? Proper storage
>> systems have sufficient battery backups built in to flush the whole cache
to
>> disk in case of power failure.
>>
>> Harel Safra
>>
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