Re: Followup comment for bug report 'postmaster ignores SIGPIPE' [was: Bug#255208: Would help with client aborts, too.]

On Mon, Mar 27, 2006 at 09:50:38AM -0500, Tom Lane wrote:
> "Jim C. Nasby" <jnasby@pervasive.com> writes:
> > On Sun, Mar 26, 2006 at 08:34:46PM -0500, Tom Lane wrote:
> >> The question is whether doing either one is really a material
> >> improvement, seeing that neither is going to provoke an abort
> >> until/unless the backend actually tries to write something to the client.
>
> > Is there a server equivalent to PQstatus? If there were one, couldn't
> > the server periodically ping the client?
>
> No, and do you really want the server stopping its processing of the
> query just to go see if the client is still alive?  This would slow
> things down and introduce a whole new failure mode, ie, client doesn't
> answer ping fast enough so its session gets aborted.

I guess it depends on how things are setup. Something like the following
probably wouldn't pose a tremendous amount of overhead...

set alarm 10 seconds;
bool ping_sent;
on alarm:
    if ping_sent then
        call to see if a ping reply is waiting for us (would this just
        sit in the network buffer, or would we actually get interrupted)
        if no ping then
            if timeout exceeded then
                abort backend;
            endif
        else
            set ping_sent = false;
        endif
    else
        ping_client();
        set ping_set = true;
    endif

Of course, the proof would be in doing some performance testing...
--
Jim C. Nasby, Sr. Engineering Consultant      jnasby@pervasive.com
Pervasive Software      http://pervasive.com    work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf       cell: 512-569-9461