RE: db file sequential read - again

From: <oracle-l-bounce_at_freelists.org>
Date: Tue, 13 Mar 2007 19:59:52 -0400
Message-ID: <AA29A27627F842409E1D18FB19CDCF270B954395@AABO-EXCHANGE02.bos.il.pqe>

Dave,

You're absolutely right! Good point. I come from a very OLTP-centric view of the world....

Here's a modified version of the query which will account for physical reads direct:
column owner format a20
column statistic_name format a15
select * from(

  select vss1.owner,
         vss1.object_name,
         vss1.statistic_name,
         vss1.value-vss2.value value,
         ds.bytes/1048576 "SEGSIZE (MB)",
         ds.buffer_pool
    from v$segment_statistics vss1,
         v$segment_statistics vss2,
         dba_segments ds
   where vss1.statistic_name ='physical reads'
     and vss2.statistic_name = 'physical reads direct'
     and ds.segment_type = vss1.object_type
     and ds.segment_name = vss1.object_name
     and ds.owner=vss1.owner
     and ds.segment_type = vss2.object_type
     and ds.segment_name = vss2.object_name
     and ds.owner=vss2.owner
     and ds.buffer_pool = 'DEFAULT'

order by (vss1.value-vss2.value) desc
)
where rownum <=20
/

Note that, while I was tinkering, I made a few other changes too:

• It no longer needs the threshold value, 5,000,000, or whatever. It will automatically return the top 20 segments w/ the most non-direct physical I/O.
• The order of the output is reversed, worst is on top.
• Segment size is displayed in MB.
• Added some reasonable column formatting, for a wide terminal (at least 132 columns)

-Mark

--
Mark J. Bobak
Senior Oracle Architect
ProQuest/CSA

"There are 10 types of people in the world:  Those who understand
binary, and those who don't."

-----Original Message-----
From: Herring Dave - dherri [mailto:Dave.Herring_at_acxiom.com] 
Sent: Tuesday, March 13, 2007 6:14 PM
To: Bobak, Mark; jherrick_at_igs.net; Wolfgang Breitling
Cc: oracle-l_at_freelists.org
Subject: RE: db file sequential read - again

Aren't 'physical reads direct' included in 'physical reads'?  If so, I
think you'd want to subtract out that value since direct reads won't be
affected by any pool definition.  Maybe that's not a big deal for most
folks, but with a DW and consequently lots of parallelism, direct reads
are the most frequent physical read, so non-direct physical reads are
important to spot for us.



> The query I came up with is:

>   select vss.owner,

>          vss.object_name,

>          vss.statistic_name,

>          vss.value,

>          ds.bytes segsize,

>          ds.buffer_pool

>     from v$segment_statistics vss,

>          dba_segments ds

>    where vss.statistic_name ='physical reads'

>      and vss.value > 5000000 ---You may need to play with this

threshold


> value for your environment

>      and ds.segment_type = vss.object_type

>      and ds.segment_name = vss.object_name

>      and ds.owner=vss.owner

>      and ds.buffer_pool = 'DEFAULT'

> order by value

> /


Dave

___________________________________

David C. Herring, DBA  |   A c x i o m  Delivery Center Organization

630-944-4762 office | 630-430-5988 wireless | 630-944-4989 fax
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Received on Tue Mar 13 2007 - 18:59:52 CDT