Re: debugging server connection issue

On 03/29/2016 01:28 PM, Stephen Constable wrote:
> My apologies, I'm not sure what part of the networking stack the
> messages are coming from. It also states:
> """
> could not connect to server: Cannot assign requested address
> Is the server running on host "<hostname>" and accepting
> TCP/IP connections on port <port>?
> """

Alright I lied, the above is a Postgres error message. I am just not
used to seeing 'Cannot assign requested address'. Turns out it is in
interfaces/libpq/win32.c.

So your client is running on Windows?

> This error is only printed under a 32-job load, never a single job load.
>
> The processes are indeed connecting over a local network.
>
> I have only enabled the logging of connections and disconnections since
> I figured that would be the most telling :) perhaps that was not the
> best idea. but, FYI, I see over 5000 such notices in a single minute.
> I will reconfigure the logging to be more verbose.
>
> Thanks,
> Steve
>
> On Tue, Mar 29, 2016 at 4:21 PM Adrian Klaver <adrian(dot)klaver(at)aklaver(dot)com
> <mailto:adrian(dot)klaver(at)aklaver(dot)com>> wrote:
>
> On 03/29/2016 01:10 PM, Stephen Constable wrote:
> > Hi All,
> >
> > I'm a new-ish sysadmin working on porting legacy scientific code
> from a
> > local server/client to new supercomputer environment. My work is
> mostly
> > done, except that my postgres database doesn't seem to be able to
> keep
> > up with the new environment. The application is written in-house
> in a
> > mixture of FORTAN 77 and C, and uses postgres BLOBS as its main data
> > store. This application in particular only reads from the
> database, it
> > never writes, which *should* make it easy to scale.
> >
> > My main problem is that this client application is unable to
> connect to
> > the database under a modest load (32 simultaneous jobs). The client
> > error logs print out messages like "could not connect to server:
> Cannot
> > assign requested address" and "Cannot connect to database
> [runlog]!!!"
> > (an important database of ours). The "cannot assign requested
> address"
>
> Well those do not look like Postgres error messages to me, so the first
> thing would be to determine what part of the stack is generating them.
>
> Is the client software connecting to the database over a network?
>
> Are you using connection pooling?
>
> > message makes me think it's a configuration issue. The logs are
> flooded
> > with hundreds of connection and disconnection notices per
> second. This
>
> Might want to turn off logging connections/disconnections:
>
> http://www.postgresql.org/docs/9.4/interactive/runtime-config-logging.html#RUNTIME-CONFIG-LOGGING-WHAT
>
> log_connections (boolean)
>
> log_disconnections (boolean)
>
> > same code and configuration runs fine on our mid-2000's Solaris
> 10 box
> > with postgres 8.4 (albeit very slowly) but totally fails with these
> > connection errors on a modern Dell system running CentOS 7 or
> FreeBSD 10
> > (I tested both) with postgres 9.4.
> >
> > While the database is under load (and jobs are actively failing),
> select
> > count(*) from pg_stat_activity returns 30-34 ish connections, show
> > max_connections returns 100, and show superuser_reserved_connections
> > shows 3. My only other hint is that right after a fresh install of
> > CentOS 7 my job success rate was around 50%, and now it has
> approached
> > approximately 5%, so something is changing over time.
> >
> > Does anyone have any advice or experience with similar issues?
>
> What else does the Postgres log show besides the
> connections/disconnections, that might be of interest?
>
> What does the system log show?
>
> >
> > Thanks,
> > Steve
> >
>
>
> --
> Adrian Klaver
> adrian(dot)klaver(at)aklaver(dot)com <mailto:adrian(dot)klaver(at)aklaver(dot)com>
>

--
Adrian Klaver
adrian(dot)klaver(at)aklaver(dot)com