Re: LISTEN/NOTIFY benchmarks?

On Tue, Apr 29, 2003 at 10:10:47AM +0300, Hannu Krosing wrote:
> prashanth@jibenetworks.com kirjutas T, 29.04.2003 kell 04:14:

> > - each client registered for thousands of LISTENs
> > 
> >     From a look at backend/commands/async.c, it would seem that each
> >     listening backend would get a signal for *every* LISTEN it
> >     registered for, resulting in thousands of signals to the same
> >     listening backend, instead of only one.
> 
> But as the signals are usually generated async, you have no way to know
> if a particular backend has already received a signal.
> 
> Or do you mean some mechanism that remembers "signals sent" in some
> shared structure that the receiving backend can then clear when it
> actually receives the signal ?

No, I meant that a listening backend process would be sent multiple
signals from a notifying process, *in the inner loop* of
backend/commands/async.c:AtCommit_Notify().

If the listening backend had registered tens of thousands of LISTENs,
it would be sent an equivalent number of signals during a single run
of AtCommit_Notify().  I'm not sure what the cost of this is, since
I'm not sure how signal delivery works, but the tens of thousands of
system calls cannot be very cheap.

--prashanth