RE: Cary/Others RE: should you seperate indexes from tables in

From: Pete Sharman <peter.sharman_at_oracle.com>
Date: Thu, 17 Jul 2003 08:01:27 +1000
Message-Id: <25937.338143@fatcity.com>

Following on from Cary's response, both internal and external testing has shown the performance improvements of storing objects in tablespaces with different block sizes to be so miniscule as to be not worth the effort (or putting it another way, there are lots of better ways to spend your performance tuning time than worrying about this).

Multiple block sizes in a single database have one purpose in life and one purpose alone - to allow transporting tablespaces between your OLTP system and a staging database before summarization of the data as it's moved into a data warehouse.

Pete

"Controlling developers is like herding cats." Kevin Loney, Oracle DBA Handbook

"Oh no, it's not. It's much harder than that!" Bruce Pihlamae, long term Oracle DBA.

-----Original Message-----
From: ml-errors_at_fatcity.com [mailto:ml-errors_at_fatcity.com] On Behalf Of Tracy Rahmlow
Sent: Wednesday, July 16, 2003 8:14 AM
To: Multiple recipients of list ORACLE-L Subject: Cary/Others RE: should you seperate indexes from tables in

Based on Cary's paper regarding when to use an index, would there not be value
in having index tablespaces with a smaller block size vs tables using a larger
block size?

AM PST Please respond to ORACLE-L_at_fatcity.com

Sent by: ml-errors_at_fatcity.com

To: "Multiple recipients of list ORACLE-L" <ORACLE-L_at_fatcity.com> cc:

The thing that occurred to me a few years ago (as a result of a test designed by Craig Shallahamer) is that "what disks do" gets very, very complicated when you add users. On any system busy enough to have a performance problem, the odds are usually slim that a disk is just "sitting
there" waiting for your next I/O call. On a busy system, someone else's I/O
call is almost always going to intercede between two of *your* I/O calls.

As has been said many times, many ways...

DO separate tables and indexes into different tablespaces. There are lots of reasons you should do this.
DON'T necessarily feel that you have to put the index and data tablespaces on different devices. One decision criterion is performance: don't ever put two files on the same device if the sum of their I/O-per-second rates exceeds the I/O-per-second capacity of the device. Another decision criterion is availability: don't ever put more data on a device than you can recover in your acceptable downtime window. The list goes on...

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

Upcoming events:

- Hotsos Clinic 101 in Washington, Denver, Sydney
- Hotsos Symposium 2004, March 7-10 Dallas
- Visit www.hotsos.com for schedule details...

-----Original Message-----
Daniel Fink
Sent: Tuesday, July 15, 2003 11:24 AM
To: Multiple recipients of list ORACLE-L

I may be way off base here, so any gurus please correct me with a gentle slap to the back of the head...

Index and table access is not as simple as index entry..table row..index entry..table row..etc. I just ran a quick test (which may not be represntative and is using the primary key which can be understood as the
row number in physical order of the data blocks) and I found (using the sequence of wait events) that there was substantial access to the index datafiles initially, followed by substantial access to the data datafiles.
Then another single access to index, multiple access to data, single access to index, multiple access to data. It seems to me that this pattern
is read several index blocks, then access several data blocks, read several
index blocks, access several data blocks. This may be due to the sequential
nature of the pk in the data blocks. It seems that the most efficient algorithm is to read enough index blocks to set up a list of data blocks to
read, then go get them. Since you have the index block pinned, don't waste
any resource in releasing the pin to pin the data blocks, then repin the index block.

The other issue is that indexes can be accessed using multiblock reads (index fast full scan) and tables can be indexed using single block reads
(table access by rowid).

Garry Gillies wrote:
>
> It's hot here. I wish I was at the beach and I feel like a rant.
>
> "oracle actually accesses indexes and tables serially"
>
> Is it just me or is this blindingly obvious?
> You cannot access the table data until you have completed accessing
the
> index data
> because the index data contains the location of the table data.
>
> During an indexed query on a single table the index will be accessed,
then
> the table,
> then the index,then the table, then the index,then the table then
the
> index,then the table.
> If the index and the table are on the same disk then a lot of time
will be
> taken up by
> head seek movement.
> If they are on the different disks then the "index" heads can locate
their
> data and stay
> there - and the "data" heads can locate their data and stay there.
> Less head movement, less wasted time.
>
> That is the argument for what it is worth. Real life is of course
vastly
> more complex than
> this and we are swimming in very muddy waters, which is why there is
so
> much
> argument on the subject (raid salesmen - spit).
>
> Thanks for the vent
>
> Garry Gillies

--
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).






American Express made the following
 annotations on 07/15/2003 02:15:07 PM
------------------------------------------------------------------------
------
************************************************************************
******

     "This message and any attachments are solely for the intended
recipient and may contain confidential or privileged information. If you
are not the intended recipient, any disclosure, copying, use, or
distribution of the information included in this message and any
attachments is prohibited.  If you have received this communication in
error, please notify us by reply e-mail and immediately and permanently
delete this message and any attachments.  Thank you."

************************************************************************
******


========================================================================
======

-- 
Please see the official ORACLE-L FAQ: http://www.orafaq.net
-- 
Author: Tracy Rahmlow
  INET: tracy.rahmlow_at_aexp.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

Received on Wed Jul 16 2003 - 17:01:27 CDT