In article <6lab0r$38q$1_at_news.interlog.com>, aau_at_interlog.com (aa) wrote:
> I have the following excepts both from Oracle seemingly in direct
> conflict
> with each other. Could someone please shed some light on it???
>
>
> From on-line Oracle 7 Server Documentation/Server Tuning/Tuning IO/How
> to
> solve IO problems/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.
>
This is ok if you can be assured that the data and index are reading from
the same disk cylinder. If not then take the advice below.
>
> From Advanced Oracle Tuning and Admin by Oracle Press, answer to test
> question at back of book:
>
> Data and indexes should be placed on different physical disks when
> possible.
> This is because typical Oracle access to an indexed table requires one
> or
> more read of the index file to determine the location of the data block
> containing the row to be accessed, follwed by a read of the appropriate
> data file block. If both of these files are on the same disk, the disk
> head
> must move from one physical area to another, and this is a relatively
> slow
> operation. I f the files are on different disks this head contention
> willl
> be reduced or eliminated. Further efficiencies may be gained by
> spreading
> both index and data tablespaces over multiple disks...
>
>
>
>
>
>
>
Luke
Received on Sat Jun 06 1998 - 10:03:27 CDT
