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Re: Hardware/OS recommendations for large databases (

From: Alan Stange <stange(at)rentec(dot)com>
To: Luke Lonergan <llonergan(at)greenplum(dot)com>
Cc: Dave Cramer <pg(at)fastcrypt(dot)com>, Greg Stark <gsstark(at)mit(dot)edu>, Joshua Marsh <icub3d(at)gmail(dot)com>, pgsql-performance(at)postgresql(dot)org
Subject: Re: Hardware/OS recommendations for large databases (
Date: 2005-11-18 17:31:33
Message-ID: 437E0FF5.5090203@rentec.com (view raw or flat)
Thread:
Lists: pgsql-performance
Luke Lonergan wrote:
> Alan,
>
> On 11/18/05 8:13 AM, "Alan Stange" <stange(at)rentec(dot)com> wrote:
>
>     I told you in my initial post that I was observing numbers in
>     excess of
>     what you claiming, but you seemed to think I didn't know how to
>     measure
>     an IO rate.
>
> Prove me wrong, post your data.
>
>     I should note too that our system uses about 20% of a single cpu when
>     performing a table scan at >100MB/s of IO. I think you claimed the
>     system would be cpu bound at this low IO rate.
>
>
> See above.
Here's the output from one iteration of iostat -k 60 while the box is 
doing a select count(1) on a 238GB table.

avg-cpu:  %user   %nice    %sys %iowait   %idle
           0.99    0.00   17.97   32.40   48.64

Device:            tps    kB_read/s    kB_wrtn/s    kB_read    kB_wrtn
sdd             345.95    130732.53         0.00    7843952          0

We're reading 130MB/s for a full minute.  About 20% of a single cpu was 
being used.   The remainder being idle.

We've done nothing fancy and achieved results you claim shouldn't be 
possible.  This is a system that was re-installed yesterday, no tuning 
was done to the file systems, kernel or storage array.

What am I doing wrong?

9 years ago I co-designed a petabyte data store with a goal of 1GB/s IO 
(for a DOE lab).   And now I don't know what I'm doing,

Cheers,

-- Alan

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