From: Greg Smith <greg@2ndquadrant.com>
To: Benjamin Krajmalnik <kraj@servoyant.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: Need some help analyzing some benchmarks
Date: Sun, 06 Feb 2011 20:36:55 -0500
Message-ID: <4D4F4CB7.50003@2ndquadrant.com> (raw)
In-Reply-To: <F4E6A2751A2823418A21D4A160B689887B0E77@fletch.stackdump.local>
References: <F4E6A2751A2823418A21D4A160B689887B0E77@fletch.stackdump.local>
Benjamin Krajmalnik wrote:
>
> My data partition is 12 drives in RAID 1+0 (2.7TB) running UFS2.
> Vfs.read_max has been set to 32, and no other tuning has been done...
>
> Not having anything to compare it to, I do not know if these are
> decent numbers or not -- they are definitely slower than a similar
> setup which was posted recently using XFS on Linux, but I have not
> found anything in FreeBSD using UFS2 to compare it to. What strikes
> me in particular is that the write performance is higher than the read
> performance -- I would have intuitively expected it to be the other
> way around.
>
Generally write speed higher than read means that volume read-ahead
still isn't high enough for the OS to keep the disk completely busy.
Try increasing read_max further; I haven't done many such tests on
FreeBSD, but as far as I know settings of 128 and 256 are generally
where read performance peaks on that OS. You should see sequential read
speed go up as you increase that parameter, eventually levelling off.
When you reach that point you've found the right setting.
--
Greg Smith 2ndQuadrant US greg@2ndQuadrant.com Baltimore, MD
PostgreSQL Training, Services, and 24x7 Support www.2ndQuadrant.us
"PostgreSQL 9.0 High Performance": http://www.2ndQuadrant.com/books
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To: pgsql-performance@postgresql.org
Cc: greg@2ndquadrant.com, kraj@servoyant.com
Subject: Re: Need some help analyzing some benchmarks
In-Reply-To: <4D4F4CB7.50003@2ndquadrant.com>
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