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Re: Low Budget Performance, Part 2

From: eric soroos <eric-psql(at)soroos(dot)net>
To: <pgsql-performance(at)postgresql(dot)org>
Subject: Re: Low Budget Performance, Part 2
Date: 2002-11-28 18:32:46
Message-ID: 30995191.1173642930@[] (view raw, whole thread or download thread mbox)
Lists: pgsql-performance
> > 
> > For 1-10 clients, IDE gets 25-30 tps, SCSI 40-50  (more with more clients, 
> > roughly linear).
> > 
> > The CPU was hardly working in these runs (~50% on scsi, ~20% on ide), vs nearly 
> > 100% on the previous run. 
> Going back to the OP, you think the CPU load is so high when using SCSI
> because of underperforming APPLE drivers?

I think it's a combination of one significant digit for cpu load and more transactions on the scsi system. I'm concluding that since the processor wasn't redlined, the bottleneck is somewhere else. Given the heavily transactional nature of these tests, it's reasonable to assume that the bottleneck is the disk. 

10 tps= 600 transactions per minute, so for the scsi drive, I'm seeing 3k transactions / 10k revolutions, for a 30% 'saturation'.  For the ide, I'm seeing 1800/7200 = 25% 'saturation'. 

The rotational speed difference is 40% (10k/7.2k), and the TPS difference is about 60% (50/30 or 40/25)

So, my analysis here is that 2/3 of the difference in transaction speed can be attributed to rotational speed. It appears that the scsi architecture is also somewhat more efficient as well, allowing for a further 20% increase (over baseline) in tps.

A test with a 7.2k rpm scsi drive would be instructive, as it would remove the rotational difference from the equation. As the budget for this is $0, donations will be accepted.


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