Re: Tables and indexes on different disks

From: Connor McDonald <hamcdc_at_yahoo.co.uk>
Date: Tue, 13 Mar 2001 09:31:53 -0800
Message-ID: <F001.002CB189.20010313092723@fatcity.com>

That argument is incorrect, but then again, so is the argument that they must be separated.

(IMHO) What really matters is having a good grasp of what I/O is happening on your db and spreading the I/O accordingly.

For example, for nested loop type of access, the table/index separation will probably give a gain. For a sort merge, then separating the tables involved is more important (since the indexes in this case may not be used at all).

Then throw in index fast full scans, hash joins, parallel slaves et al and things get all the more complicated.

I think the *intentions* behind all the tuning doco we all typically see is valid - namely, try to control and balance your I/O.

Cheers
Connor

• Michal Zaschke <zaschke_at_suas.cz> wrote: > Hi all,
  >
  > I've read an interesting section in Oracle Docu
  > (Tuning I/O):
  >
  > ---
  > Separating Tables and Indexes
  >
  > It is not necessary to separate a frequently used
  > table from its index.
  > During the course of a transaction, the index is
  > read first, and then
  > the table is read. Because these I/Os occur
  > sequentially, the table and
  > index can be stored on the same disk without
  > contention.
  > ---
  >
  > Why do you then recommend to separate tables and
  > indexes to different
  > disks?
  >
  > Thanks
  > Mike
  > --
  > Please see the official ORACLE-L FAQ:
  > http://www.orafaq.com
  > --
  > Author: Michal Zaschke
  > INET: zaschke_at_suas.cz
  >
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Connor McDonald
http://www.oracledba.co.uk

"Some days you're the pigeon, some days you're the statue"

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Received on Tue Mar 13 2001 - 11:31:53 CST