Re: postgresql 8 abort with signal 10

On 5/3/05, Scott Marlowe <smarlowe@g2switchworks.com> wrote:
> On Tue, 2005-05-03 at 11:36, Alexandre Biancalana wrote:
> > >>You need to find out what's triggering that.  Turning on query logging
> > >>would be a good way of investigating.
> >
> >  Which directives can I use to enable this ?
> > debug_print_parse ? debug_print_rewritten ? debug_print_plan ?
> > debug_pretty_print ?
> >
> >
> > >>Rather large, shared buffers for a machine with only 1 gig of ram.  640
> > >>Meg of RAM means the kernel is basically double buffering everything.
> > >>have you tested with smaller settings and this setting was the best?
> >
> > I had 256 of RAM then I increase to 1GB thinking this could be a
> > problem of out of memory or a buggy memory...... After this "upgrade"
> > I increase the numbers of shared buffers,etc
> >
> > It's important to say that the max memory usage reach to only 80%.
> >
> > What values do you suggest ?
>
> Generally 25% of the memory or 256 Megs, whichever is less. In your
> case, they're the same.  The Reasoning being that the kernel caches,
> while postgresql only really holds onto data as long as it needs it,
> then frees it, so having a really huge buffer space lets postgresql
> flush the kernel cache, then the next access, after postgresql has freed
> the memory that was holding the data, now has to go to disk.
>
> The kernel is generally a lot better at caching than most apps.
>
> So, 32768 is about as big as i'd normally go, and even that may be more
> than you really need.  Note that there's overhead in managing such a
> large buffer as well.  With pgsql 8.x and the new caching algorithms in
> place, such overhead may be lower, and larger buffer settings may be in
> order.  But if testing hasn't shown them to be faster, i'd avoid them
> for now and see if your signal 10 errors start going away.
>
> If they do, then you've likely got a kernel bug in there somewhere.  If
> they don't, I'd suspect bad hardware.
>
> > >>You might want to look in your signal man page on BSD and see what
> > >>signal 10 means.  On solaris it's a bus error.  Not a clue what it is in
> > >>FreeBSD myself though.
> >
> > FreeBSD man page say: 10    SIGBUS
> >
> > The system does not generate core dump file for this error.....
>
>

Hi Michael,

Here is my /etc/sysctl.conf:

kern.corefile="/var/coredumps/%N.%P.core"
kern.sugid_coredump=1

and how I said before, there is no one core file in /var/coredumps....
I should say that this structure to store core files it's ok, in past
I used this a lot....

Thanks Scott I will lower shared_buffers to 32768 and try again, but
how about work_mem, maintenance_work_mem, effective_cache_size ??