Re: Inconsistent file IO times on AWR report

Even if you're using direct io it still could be caching at the storage level. 
What is your disk/lun configuration?

Harel Safra

On 04/05/2010 16:11, Stephens, Chris wrote:
Since blocks from the heaviest hit tablespace are more likely to be in the os-cache, that would account for Oracle thinking blocks read from that tablespace are faster. I guess that assumes you aren't using direct-io. 

Chris
*From:* oracle-l-bounce@xxxxxxxxxxxxx [mailto:oracle-l-bounce@xxxxxxxxxxxxx] *On Behalf Of *Neil Kodner 
*Sent:* Tuesday, May 04, 2010 7:35 AM
*To:* oracle-l-freelists; Neil Kodner
*Subject:* Inconsistent file IO times on AWR report
I'm trying to get to the bottom of some performance issues and one of the things that stumps me is that my AWR reports show wildly inconsistent read times for my tablespaces. The heaviest-hit tablespace consistently shows an average read time of .59ms. The others range from 13 to 25ms in avg read time. I dont find anything obvious when comparing matviews_index and matviews_data to the rest of the tablespaces when looking in dba_tablespaces.
Given that all of the tablespaces are on the same hardware device and mount points, I would expect the average read times to be somewhat similar across the board. Is this an invalid assumption?
The tablespace and file details from awr can be found at http://goo.gl/CTaO 

I'll update the document with additional information as requested.

Thanks,

Neil


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