Re: zLinux Load Testing Experience

On Wed, May 1, 2013 at 8:01 AM, Andrew Hastie <andrew@ahastie.net> wrote:

On 30/04/13 20:46, Merlin Moncure wrote:

On Tue, Apr 30, 2013 at 12:26 PM, Jeff Janes <jeff.janes@gmail.com> wrote:

On Tue, Apr 30, 2013 at 8:28 AM, Andrew Hastie <andrew@ahastie.net>
wrote:

I'm currently working on a project porting an application from RedHat
Linux on Intel onto IBM zLinux. Our application requires PostgreSQL at
version 9.n, so the PostgreSQL binaries have been built using the
standard
build tools from source. Everything appears run correctly. However as
part
of performance testing, our IBM and Linux SysProgs have been "poking
around"
using strace and have reported the following (which they think is an
error
condition) when hooking up to the postmaster processes:-

read(3, 0x3ffff875ee0, 16) = -1 EAGAIN (Resource temporarily
unavailable)
poll([{fd=3, events=POLLIN}, {fd=6, events=POLLIN}], 2, 200) = 0
(Timeout)
read(3, 0x3ffff875ee0, 16) = -1 EAGAIN (Resource temporarily
unavailable)
poll([{fd=3, events=POLLIN}, {fd=6, events=POLLIN}], 2, 10000) = 0
(Timeout)
... repeated many times

That does not look like the postmaster process.  It looks like probably
the
background writer process.

It is normal, and doesn't explain high CPU utilization.

yeah: we're probably a couple of steps in front of deep system
profiling.   Helpful things to provide to help diagnose would be:

*) 'explain analyze' of the queries that are eating cpu
*) more details about the hardware -- how many cpu, etc.
*) better definition of 'perceived high CPU utilisation'
*) some correlating performance tests, expecially cpu bound pgbench
tests (pgbench -S)

merlin

I'm not sure how much experience the community has on tuning PostgreSQL
running on RedHat which in turn is hosted on an IBM mainframe under VM
(using zLinux). So I'm happy to start posting further details and benchmark
results and see where we go. Should I be moving this thread over into the
pg-performance list, or is pg-general the right place?

certainly performance.   and yes, zLinux is less well traveled.  Did
you compile postgres from source?  Did you confirm that there is a
native spinlocks implementation and it is being used?

merlin

Did you compile postgres from source? - Yes (I need PG v9.n as v8.n shipped with RedHat Ent6 does not have several v9 specific features we need).

Did you confirm that there is a native spinlocks implementation and it is being used? - I believe so as no errors or warnings logged during the build. Is there a simple way to check whether spin-locks are running native?

I've started looking at several articles covering pgbench and running some initial tests, so I plan to start a new thread on pg-performance in the next day or so.

Thanks for the advice so far  - Appreciated :-)

Andrew