Re: postgresql + apache under heavy load

Alex Madon wrote:

> Hello,
> I am testing a web application (using the DBX PHP function to call a
> Postgresql backend).
> I have 375Mb RAM on my test home box.
> I ran ab (apache benchmark) to test the behaviour of the application
> under heavy load.
> When increasing the number of requests, all my memory is filled, and
> the Linux server begins to cache and remains frozen.
>
> ab -n 100 -c 10 http://localsite/testscript
> behaves OK.
>
> If I increases to
> ab -n 1000 -c 100 http://localsite/testscript
> I get this memory problem.

We would need a lot more information. What version of Linux? What
version of the Kernel? What is your shmmax settting?
What is your sort_mem setting? Did you use top to see where the hang up?
Are there any messages in /var/log/messages?

Sincerely,

Joshua D. Drake

>
> If I eliminate the connection to the (UNIX) socket of Postgresql, the
> script behaves well even under very high load (and of course with much
> less time spent per request).
>
> I tried to change some parameters in postgresql.conf
> max_connections = 32
> to max_connections = 8
>
> and
>
> shared_buffers = 64
> to shared_buffers = 16
>
> without success.
>
> I tried to use pmap on httpd and postmaster Process ID but don't get
> much help.
>
> Does anybody have some idea to help to debug/understand/solve this
> issue? Any feedback is appreciated.
> To me, it would not be a problem if the box is very slow under heavy
> load (DoS like), but I really dislike having my box out of service
> after such a DoS attack.
> I am looking for a way to limit the memory used by postgres.
>
> Thanks
> Alex
>
>
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