Re: listen/notify argument (old topic revisited)

On Tue, 2002-07-02 at 23:35, Tom Lane wrote:
> Bruce Momjian <pgman@candle.pha.pa.us> writes:
> > Is disk i/o a real performance
> > penalty for notify, and is performance a huge issue for notify anyway,
> 
> Yes, and yes.  I have used NOTIFY in production applications, and I know
> that performance is an issue.
> 
> >> The queue limit problem is a valid argument, but it's the only valid
> >> complaint IMHO; and it seems a reasonable tradeoff to make for the
> >> other advantages.
> 
> BTW, it occurs to me that as long as we make this an independent message
> buffer used only for NOTIFY (and *not* try to merge it with SI), we
> don't have to put up with overrun-reset behavior.  The overrun reset
> approach is useful for SI because there are only limited times when
> we are prepared to handle SI notification in the backend work cycle.
> However, I think a self-contained NOTIFY mechanism could be much more
> flexible about when it will remove messages from the shared buffer.
> Consider this:
> 
> 1. To send NOTIFY: grab write lock on shared-memory circular buffer.

Are you planning to have one circular buffer per listening backend ?

Would that not be waste of space for large number of backends with long
notify arguments ?

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Hannu