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
Date: Wed, 19 Apr 2006 00:13:47 -0500
Message-ID: <20060419051346.GQ49405@pervasive.com> (raw)
In-Reply-To: <4445A1DF.6000705@elde.net>
References: <85979594-1CCA-43C5-A8F2-08685CF41ACE@pervasive.com>
<443F3BB3.30404@elde.net>
<20060418200641.GG49405@pervasive.com>
<4445A1DF.6000705@elde.net>
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
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To: pgsql-performance@postgresql.org
Cc: jnasby@pervasive.com, terje@elde.net
Subject: Re: Blocks read for index scans
In-Reply-To: <20060419051346.GQ49405@pervasive.com>
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