RE: db file sequential read - again
- To: "Herring Dave - dherri" <Dave.Herring@xxxxxxxxxx>, <jherrick@xxxxxxx>, "Wolfgang Breitling" <breitliw@xxxxxxxxxxxxx>
- Date: Tue, 13 Mar 2007 19:59:52 -0400
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@xxxxxxxxxx]
Sent: Tuesday, March 13, 2007 6:14 PM
To: Bobak, Mark; jherrick@xxxxxxx; Wolfgang Breitling
Cc: oracle-l@xxxxxxxxxxxxx
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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