Re: How to calculate the exact cost of a physical read

From: Andrew Mobbs <andrewm_at_chiark.greenend.org.uk>
Date: 09 Aug 2001 15:59:34 +0100 (BST)
Message-ID: <cDi*vLk3o@news.chiark.greenend.org.uk>

Garry Robinson <garry_robinson_at_slc.co.uk> wrote:
>Does anyone know how to calculate the average duration of a physical
>block read from disk?
>Can V$SYSTEM_EVENT.AVERAGE_WAIT_TIME for db_file_sequential_read event
>be relied on to represent the average time taken to transfer a random
>block from disk to the buffer cache?

IME, sort of. There's a corellation between the Oracle data and the system data, but the numbers don't always match exactly.

For details of disk performance, you're probably better off using the system monitoring tools. I always collect both data. You don't say what platform you're using, but "sar" on many versions of UNIX will give fairly good data, "iostat" on Solaris is a bit more detailed. On NT/W2k there's the performance monitor GUI. Any other platform, you're on your own but such tools probably exist.

-- 
Andrew Mobbs - http://www.chiark.greenend.org.uk/~andrewm/

Received on Thu Aug 09 2001 - 09:59:34 CDT