Re: Hyperthreading (was: Two identical systems, radically different performance)

On 10/09/2012 06:30 PM, Craig James wrote:

> ra:8192 walb:1M ra:256 walb:1M ra:256 walb:256kB
> ---------------- ---------------- -----------------
> -c -t Run1 Run2 Run3 Run4 Run5 Run6 Run7 Run8 Run9
> 40 2500 4261 3722 4243 9286 9240 5712 9310 8530 8872
> 50 2000 4138 4399 3865 9213 9351 9578 8011 7651 8362

I think I speak for more than a few people here when I say: wat.

About the only thing I can ask, is: did you make these tests fair? And
by fair, I mean:

echo 3 > /proc/sys/vm/drop_caches
pg_ctl -D /your/pg/dir restart

Between every test to make sure shared buffers and the OS inode cache
was empty before the start of each test? If you're using that bash-style
for-loop you attached earlier, probably not. Still though, I don't think
that would account for this much variance between having read-ahead at
8M as opposed to 256kb.

My head hurts.

--
Shaun Thomas
OptionsHouse | 141 W. Jackson Blvd. | Suite 500 | Chicago IL, 60604
312-444-8534
sthomas(at)optionshouse(dot)com

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