Re: Hyperthreading (was: Two identical systems, radically different performance)
Sent this to Claudio rather than the whole list ... here it is.
Big numbers, little numbers ... I'm just reporting what pgbench tells me and how I got them. I'm good at chemical databases, you guys are the Postgres performance experts.
On Wed, Oct 10, 2012 at 7:44 AM, Claudio Freire <klaussfreire@gmail.com> wrote:
I showed the exact commands I used -- if it's not there, I didn't do it. So the answer is no, I didn't drop caches.
On the other hand, I wanted to know what happened on cold start and after running for a while. Running pgbench once isn't as interesting as running it three times.
On Wed, Oct 10, 2012 at 9:52 AM, Shaun Thomas <sthomas@optionshouse.com> wrote:
> 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
I showed the exact commands I used -- if it's not there, I didn't do it. So the answer is no, I didn't drop caches.
On the other hand, I wanted to know what happened on cold start and after running for a while. Running pgbench once isn't as interesting as running it three times.
Yes, I was thinking the same. Especially if you check the tendency to
perform better in higher-numbered runs. But, as you said, that doesn't
explain that jump to twice the TPS. I was thinking, and I'm not
pgbench expert, could it be that the database grows from run to run,
changing performance characteristics?
> My head hurts.
I'm just confused. No headache yet.
But really interesting numbers in any case. It these results are on
the level, then maybe the kernel's read-ahead algorithm isn't as
fool-proof as we thought? Gotta read the source. BRB
Big numbers, little numbers ... I'm just reporting what pgbench tells me and how I got them. I'm good at chemical databases, you guys are the Postgres performance experts.
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