Re: Sequential Scan Read-Ahead

On Thu, 25 Apr 2002, Curt Sampson wrote:

> Here's the ratio table again, with another column comparing the
> aggregate number of requests per second for one process and four
> processes:
>

Just for interest, I ran this again with 20 processes working
simultaneously. I did six runs at each blockread size and summed
the tps for each process to find the aggregate number of reads per
second during the test. I dropped the higest and the lowest ones,
and averaged the rest. Here's the new table:

		1 proc	4 procs	20 procs

    1 block	310	440	260
    2 blocks	262	401	481
    4 blocks	199	346	354
    8 blocks	132	260	250
    16 blocks	 66	113	116

I'm not sure at all why performance gets so much *worse* with a lot of
contention on the 1K reads. This could have something to with NetBSD, or
its buffer cache, or my laptop's crappy little disk drive....

Or maybe I'm just running out of CPU.

cjs
-- 
Curt Sampson  <cjs@cynic.net>   +81 90 7737 2974   http://www.netbsd.org
    Don't you know, in this new Dark Age, we're all light.  --XTC