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Home -> Community -> Mailing Lists -> Oracle-L -> RE: How do I get the Physical Reads
Jai - I'm no expert in this area, but maybe I can help a little, and maybe
that will help you refine your question for the people that are truly expert
in this area. You are correct that Physical Reads is the number of blocks
Oracle requested from the O.S. That is as far as Oracle can see. To go
further, you must look to the O.S. side. The information available there is
first of all O.S. dependent, and you didn't specify your O.S. Next, it is
dependent on your I/O system configuration. For one thing, unless you are
using raw devices, the O.S. may do a little caching and buffering itself.
Then your I.O. system may have a cache of its own. Depending on your O.S.,
there will be a command (such as iostat in most Unix varieties) to track I/O
usage. I haven't found a block-for-block match between Oracle's statistics and O.S. statistics. But I have usually been able to get some correlations going. When Oracle says it is performing a lot of I/O, the O.S. also shows alot of I/O.
Oracle may not be the only application that is running on the system. If Oracle says it is doing relatively little I/O, and your disk system is smoking from all the activity, you might want to check that out.
But the really important thing to consider is the fact that for most systems, you have more than one I/O device. Hopefully you have several. There are other parts of report.txt that show the I/O to each file. That can help you balance the I/O load between devices, which is your real objective.
And finally, I would recommend that you investigate STATSPACK. Utlestat only works well with Server Manager (svrmgr) because of the way it formats report.txt, and once you upgrade to 9i you don't have Server Manager anymore.
Dennis Williams
DBA, 40%OCP
Lifetouch, Inc.
dwilliams_at_lifetouch.com
-----Original Message-----
Sent: Wednesday, January 01, 2003 3:24 AM
To: Multiple recipients of list ORACLE-L
Hi all,
>From the Report.txt that I analysed, I found that the Physical Reads
is 350215. I understand that this value denotes the number of
I/O requests given by Oracle to the OS to obtain the Data Blocks that
it requires. This is infact a Buffer Cache Miss in that case.
I would like to know how I can find out the actual Disk I/O that has occured for READ from Oracle. Wouldn't it be the same as the value indicated by Physical Reads in Report.txt , if the File System Block Size is the same as the DB Block Size.
Best Regards
Jai
-- Please see the official ORACLE-L FAQ: http://www.orafaq.net -- Author: DENNIS WILLIAMS INET: DWILLIAMS_at_LIFETOUCH.COM Fat City Network Services -- 858-538-5051 http://www.fatcity.com San Diego, California -- Mailing list and web hosting services --------------------------------------------------------------------- To REMOVE yourself from this mailing list, send an E-Mail message to: ListGuru_at_fatcity.com (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB ORACLE-L (or the name of mailing list you want to be removed from). You may also send the HELP command for other information (like subscribing).Received on Wed Jan 01 2003 - 08:53:51 CST
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