Oracle-L: RE: BAARF

From: Cary Millsap <cary.millsap_at_hotsos.com>
Date: Mon, 29 Sep 2003 07:09:55 -0800
Message-ID: <F001.005D15ED.20030929070955@fatcity.com>

Thomas,

It *is* a good idea to separate index data from heap data into different tablespaces. But the reason isn't solely to eliminate I/O competition. Even if I/O competition isn't an issue for you (and the OFA Standard doesn't say that it will be), then it's *still* a good idea to separate your index data from your heap data, for reasons including:

Index segments have different backup and recovery requirements than their corresponding heap segments. For example, as Peter mentioned, if you have an index block corruption event, then it's convenient to just offline, kill, and rebuild an index tablespace. If the indexes and data are mixed up in a single tablespace, this is not an option. Another example: If you construct your backup schedule to make media recovery time a constant, then you probably don't need to back up your indexes on the same schedule as you back up your heaps. But unless they're in different tablespaces, this isn't an option either.
Index segments are usually smaller than their corresponding heap segments. Using separate tablespaces allows you to use a smaller extent size to conserve disk storage capacity.

I don't think I ever wrote that you need to put indexes and their corresponding tables/clusters on separate disks, but you do need to be *able* to do that if your I/O rates indicate that you should.

For the original OFA Standard definition, please see section 3 of the document called "The OFA Standard--Oracle for Open Systems," and section 5 of "Configuring Oracle Server for VLDB," both available for free at www.hotsos.com.

Cary Millsap
Hotsos Enterprises, Ltd.
http://www.hotsos.com

Upcoming events:

- Performance Diagnosis 101: 10/28 Phoenix, 11/19 Sydney
- Hotsos Symposium 2004: March 7-10 Dallas
- Visit www.hotsos.com for schedule details...

-----Original Message-----
Thomas Day
Sent: Monday, September 29, 2003 9:05 AM To: Multiple recipients of list ORACLE-L

My struggle is not with the directory layout OFA.

It is with the "mythical" OFA that every DBA that I have talked to knows all about. Where ORACLE says that if you are a good and competent DBA you
will separate your table data and your index data into two separate tablespaces so that one disk head can be reading index entries while another disk head is reading the table data. You've never run into that?

                      Tim Gorman <tim

                      @sagelogix.com>          To:      Multiple
recipients of list ORACLE-L <ORACLE-L_at_fatcity.com>                    
                      Sent by:                 cc:

                      ml-errors                Subject: Re: BAARF

 

 

                      09/28/2003 09:44

                      PM

                      Please respond

                      to ORACLE-L

Thomas,

Please pardon me, but you are off-target in your criticisms of OFA.

It has never advocated separating tables from indexes for performance purposes. Ironically, your email starts to touch on the real reason for separating them (i.e. different types of I/O, different recovery requirements, etc). Tables and indexes do belong in different tablespaces,
but not for reasons of performance.

Cary first designed and implemented OFA in the early 90s and formalized it
into a paper in 1995. Quite frankly, it is a brilliant set of rules of how
Oracle-based systems should be structured, and a breath of fresh air from
the simplistic way that Oracle installers laid things out at the time. It
took several years for Oracle Development to see the light and become OFA-compliant, and not a moment too soon either. Just imagine if everything
were still installed into a single directory tree under ORACLE_HOME? All
of things you mention here have nothing to do with OFA.

Please read the paper.

Hope this helps...

-Tim

P.S. By the way, multiple block sizes are not intended for performance

optimization; they merely enable transportable tablespaces between

databases with different block sizes.

on 9/25/03 11:04 AM, Thomas Day at tday6_at_csc.com wrote:

>
> I would love to have a definitive site that I could send all RAID-F
> advocates to where it would be laid out clearly, unambiguously, and
> definitively what storage types should be used for what purpose.
>
> Redo logs on RAID 0 with Oracle duplexing (y/n)?
> Rollback (or undo) ditto?
> Write intensive tablespaces on RAID 1+0 (or should that be 0+1)?
> Read intensive tablespaces on RAID ? (I guess 5 is OK since it's
cheaper
> than 1+0 and you won't have the write penalty)
>
> While we're at it could we blow up the OFA myth? Since you're
tablespaces
> are on datafiles that are on logical volumns that are on physical
devices
> which may contain one or many actual disks, does it really make sense
to
> worry (from a performance standpoint) about separating tables and
indexes
> into different tablespaces?
>
> We have killed the "everything in one extent" myth haven't we?
Everybody's
> comfortable with tables that have 100's of extents?
>
> And while we're at it, could we include the Oracle 9 multiple
blocksizes
> and how to use them. The best that I've seen is indexes in big
blocks,
> tables in small blocks --- uh, oh, time to separate tables and
indexes.
>
> Maybe we will never get rid of the OFA myth.
>
> Just venting.
>
> Tired of arguing in front of management with Oracle certified DBAs
that
> RAID 5 is not good, OFA is unnecessary, and uniform extents is the
only
way
> to go. Looking for a big stick to catch their attention with.
>

--
Please see the official ORACLE-L FAQ: http://www.orafaq.net
--
Author: Tim Gorman
  INET: tim_at_sagelogix.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).





-- 
Please see the official ORACLE-L FAQ: http://www.orafaq.net
-- 
Author: Thomas Day
  INET: tday6_at_csc.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).


-- 
Please see the official ORACLE-L FAQ: http://www.orafaq.net
-- 
Author: Cary Millsap
  INET: cary.millsap_at_hotsos.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 Mon Sep 29 2003 - 10:09:55 CDT