Re: Blocks read for index scans

On Wed, Apr 19, 2006 at 04:35:11AM +0200, Terje Elde wrote:
> Jim C. Nasby wrote:
> >>That said, it's the transactions against disk that typically matter. On
> >>FreeBSD, you can get an impression of this using 'systat -vmstat', and
> >>watch the KB/t column for your drives.
> >>
> >
> >On a related note, you know of any way to determine the breakdown
> >between read activity and write activity on FreeBSD? vmstat, systat,
> >iostat all only return aggregate info. :(
> >
>
>
> Can't think of a right way to do this ATM, but for a lab-type setup to
> get an idea, you could set up a gmirror volume, then choose a balancing
> algorithm to only read from one of the disks. The effect should be that
> writes go to both, while reads only go to one. Activity on the
> write-only disk would give you an idea of the write activity, and
> (read/write disk - write-only disk) would give you an idea of the
> reads. I have to admit though, seems like quite a bit of hassle, and
> I'm not sure how good the numbers would be, given that at least some of
> the info (KB/transaction) are totals, it'd require a bit of math to get
> decent numbers. But at least it's something.

Yeah... not gonna happen...

It's completely mind-boggling that FBSD doesn't track writes and reads
seperately.
--
Jim C. Nasby, Sr. Engineering Consultant jnasby(at)pervasive(dot)com
Pervasive Software http://pervasive.com work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf cell: 512-569-9461