Re: Databse File layout on only 4 drives Ideas?

From: OctoPrime <OctoPrime_at_NOSPAMWhiteHouse.gov>
Date: Wed, 29 Jan 2003 14:14:23 -0500
Message-ID: <pan.2003.01.29.19.14.19.564155.379@NOSPAMWhiteHouse.gov>

On Tue, 28 Jan 2003 01:16:12 -0500, Howard J. Rogers wrote:

> "Joel Garry" <joel-garry_at_home.com> wrote in message
> news:91884734.0301271412.19f50e14_at_posting.google.com...

>> Mark Townsend <markbtownsend_at_attbi.com> wrote in message

> news:<BA5775D0.6EBA%markbtownsend_at_attbi.com>...

>> > in article AepY9.54719$L47.8070994_at_read2.cgocable.net, David Platt at
>> > david-platt_at_cogeco.ca wrote on 1/24/03 9:26 PM:
>> >
>> > > I am quite curious as to why a couple of you have written off the
>> > > idea

> of

>> > > splitting data and index across drives.  This is a practise that I

> have

>> > > followed for a while and I am wondering why it is being written off
>> > > so quickly
>> >
>> >
>> > First check the following -
>> > http://otn.oracle.com/deploy/availability/pdf/oow2000_same.pdf
>>
>> Which says: "Any access hot-spot that is smaller than a megabyte should
>> fit comfortably in the database buffer cache.  Therefore it will not
>> create a hot-spot on disk."
>>
>> I've always had a problem with this statement.  Wouldn't a db buffer
>> cache hot-spot like this be a "dirty write" attractor, often flushing
>> and making a hot-spot on the disk?

>
> No, because there's no relationship between the adjacent-ness of blocks
> on disk and what DBWR decides to flush.
>
> (Which, I hate to mention it, explains why indexes and tables don't
> necessarily have to be separated. They might be read together (or close
> in time together, anyway), but that doesn't mean they will be *written*
> similarly).
>
> I didn't read the original link, however, so I may have taken your
> comments out of context.
>
> HJR
  In the old days tables and indexes needed to be separated so the index and the table could be read at the same time. These days with RAID and striping it's not that big of a deal because you will have sveral rw heads working in concert which gives you performance above that of two disk, one with tables and one with indexes.

Prime Received on Wed Jan 29 2003 - 13:14:23 CST