Re: Ubuntu 12.04 / 3.2 Kernel Bad for PostgreSQL Performance

On 05/12/2012 18:28, Shaun Thomas wrote:
> Hey guys,
>
> This isn't a question, but a kind of summary over a ton of investigation
> I've been doing since a recent "upgrade". Anyone else out there with
> "big iron" might want to confirm this, but it seems pretty reproducible.
> This seems to affect the latest 3.2 mainline and by extension, any
> platform using it. My tests are restricted to Ubuntu 12.04, but it may
> apply elsewhere.
>
Very interesting results, I've been trying to benchmark my box but
getting what I would call poor performance given the setup, but I am
running 3.2 on ubuntu 12.04. Could I ask what hardware (offline if you
wish) was used for the results below?
> Comparing the latest official 3.2 kernel to the latest official 3.4
> kernel (both Ubuntu), there are some rather striking differences. I'll
> start with some pgbench tests.
>
> * This test is 800 read-only clients, with 2 controlling threads on a
> 55GB database (scaling factor of 3600) for 3 minutes.
>   * With 3.4:
>     * Max TPS was 68933.
>     * CPU was between 50 and 55% idle.
>     * Load average was between 10 and 15.
>   * With 3.2:
>     * Max TPS was 17583. A total loss of 75% performance.
>     * CPU was between 12 and 25% idle.
>     * Load average was between 10 and 60---effectively random.
>   * Next, we checked minimal write tests. This time, with only two
> clients. All other metrics are the same.
>     * With 3.4:
>       * Max TPS was 4548.
>       * CPU was between 88 and 92% idle.
>       * Load average was between 1.7 and 2.5.
>     * With 3.2:
>       * Max TPS was 4639.
>       * CPU was between 88 and 92% idle.
>       * Load average was between 3 and 4.
>
TIme to see what a 3.4 kernel does to my setup I think?

Thanks

John