Re: Temp (sort) on Raid 5....

Gosh-- who would have thought? I have no preference other than the truth. I will get to work on this SQL when I get back from vacation on Nov 6th.. As usual.. I greatly appreciate everyone's input. Learn something new every day.. or at least every week.. Thanks,
Dc.

On Thu, 26 Oct 2000 08:07:50 -0000, "Jonathan Lewis" <jonathan_at_jlcomp.demon.co.uk> wrote:

>
>Not a lot of people know this, but many RAID-5
>implementations these days can be tuned quite
>nicely for sort/temp.
>
>The biggest complaint made about RAID-5 is the
>double write cost: you write the block and you
>read, recalculate, and rewrite the parity.
>
>But if you do a full stripe write (i.e. the right N-1
>discs), then the subsystem can calculate the
>totally new parity in memory and write the whole
>stripe with just a 1 in N overhead.
>
>So with suitable configuration you can prove that
>RAID-5 is appalling, or RAID-5 if fine - what's your
>preference ?
>
>
>To prove your point - write a piece of SQL that
>does a Cartesian sort-merge on about 10,000
>rows, then groups the intermediate set to about
>10,000 rows - this should be low on disc activity
>other than sorting. Set Sort_area_size to 512K,
>and watch v$session_event for 'direct write' waits.
Received on Fri Oct 27 2000 - 00:34:45 CDT