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Home -> Community -> Mailing Lists -> Oracle-L -> RE: Why "Separating Data and Indexes improves performance" is a myth?
duh - of course. =20
-----Original Message-----
From: oracle-l-bounce_at_freelists.org
[mailto:oracle-l-bounce_at_freelists.org]On Behalf Of Nelson, Allan
Sent: Friday, April 23, 2004 2:48 PM
To: oracle-l_at_freelists.org
Subject: RE: Why "Separating Data and Indexes improves performance" is a
myth?
You should also separate rollback segments and temp space as they have markedly different use patterns as opposed to data and index segments. Rollback segments tend to be written from beginning to end and over again and temp also tends to be sequential type i/o
Allan
-----Original Message-----
=3D46rom: oracle-l-bounce_at_freelists.org
[mailto:oracle-l-bounce_at_freelists.org] On Behalf Of
Paula_Stankus_at_doh.state.fl.us
Sent: Friday, April 23, 2004 1:40 PM
To: oracle-l_at_freelists.org
Subject: RE: Why "Separating Data and Indexes improves performance" is a
myth=3D3F
So in laying out disks for a new database - perhaps the only thing worth
=3D3D
separate out is the redo based on I/O contention - right=3D3F =3D3D20
-----Original Message-----
=3D46rom: oracle-l-bounce_at_freelists.org
[mailto:oracle-l-bounce_at_freelists.org]On Behalf Of Stankus, Paula G
Sent: Friday, April 23, 2004 2:38 PM
To: oracle-l_at_freelists.org
Subject: RE: Why "Separating Data and Indexes improves performance" is a
myth=3D3F
Daniel,
Clear explanation. =3D3D3D20
And if 42 sessions are likely reading the same block at the same time =
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=3D3D3D
then wouldn't it be better to have more disks for the RAID stripe - then
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=3D3D3D
to sacrifice those disks for the indexes=3D3F
-----Original Message-----
=3D46rom: oracle-l-bounce_at_freelists.org
[mailto:oracle-l-bounce_at_freelists.org]On Behalf Of Daniel Fink
Sent: Friday, April 23, 2004 1:15 PM
To: oracle-l_at_freelists.org
Subject: Re: Why "Separating Data and Indexes improves performance" is a
myth=3D3F
In a test using a range scan on a non-unique index, I found the =3D3D3D
=3D66ollowing
sequence. The index is a normal b-tree, so the process may be different
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=3D3D3D
=3D66or
bitmaps, IOTs, etc.
So, the data and index is not physically accessed at the same time.
However, at the time session 1 is performing step 2, session 2 may be
performing step 1, so the data and index may be read at the same time, =
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=3D3D3D
but by
different sessions. Of course, you could also have 42 sessions each =
=3D3D3D
reading
the same data block at the same time.
Daniel Fink
Wolfgang Breitling wrote:
> The myth is that "they are both accessed at the same time". They are =
=3D3D
=3D3D3D
not.
> At least not by the same session processing a single sql statement. > > At 10:13 AM 4/23/2004, you wrote: > >Hi > >Does any one kwnows please, > >Why "Separating Data and Indexes improves performance" is a myth=3D3F > > > >If they are both accesed at the same time, it will improve =3D3D3Dperformance or
> >not, > >I don't understand exactly what is this myth about=3D3F > > > >http://www.niall.litchfield.dial.pipex.com/OracleMyths.zip > > > >Thanks > > > > > >Juan Carlos Reyes Pacheco > >OCP > >Database 9.2 Standard Edition > > > > > >---------------------------------------------------------------- > >Please see the official ORACLE-L FAQ: http://www.orafaq.com > >---------------------------------------------------------------- > >To unsubscribe send email to: oracle-l-request_at_freelists.org > >put 'unsubscribe' in the subject line. > >-- > >Archives are at http://www.freelists.org/archives/oracle-l/ > >FAQ is at http://www.freelists.org/help/fom-serve/cache/1.html > >----------------------------------------------------------------- > > regards > > Wolfgang Breitling > Centrex Consulting Corporation > www.centrexcc.com > > ---------------------------------------------------------------- > Please see the official ORACLE-L FAQ: http://www.orafaq.com > ---------------------------------------------------------------- > To unsubscribe send email to: oracle-l-request_at_freelists.org > put 'unsubscribe' in the subject line. > -- > Archives are at http://www.freelists.org/archives/oracle-l/ > FAQ is at http://www.freelists.org/help/fom-serve/cache/1.html > ----------------------------------------------------------------- ----------------------------------------------------------------Please see the official ORACLE-L FAQ: http://www.orafaq.com
-- Archives are at http://www.freelists.org/archives/oracle-l/Received on Fri Apr 23 2004 - 13:53:08 CDT
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