Date: Wed, 19 Apr 2006 00:13:47 -0500
From: "Jim C. Nasby" <jnasby@pervasive.com>
To: Terje Elde <terje@elde.net>
Cc: pgsql-performance@postgresql.org
Subject: Re: Blocks read for index scans
Message-ID: <20060419051346.GQ49405@pervasive.com>
References: <85979594-1CCA-43C5-A8F2-08685CF41ACE@pervasive.com>
	<443F3BB3.30404@elde.net> <20060418200641.GG49405@pervasive.com>
	<4445A1DF.6000705@elde.net>
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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@pervasive.com
Pervasive Software      http://pervasive.com    work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf       cell: 512-569-9461