| From: | Alvaro Herrera <alvherre(at)commandprompt(dot)com> |
|---|---|
| To: | Andrew Dunstan <andrew(at)dunslane(dot)net> |
| Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: Notify enhancement |
| Date: | 2006-12-15 21:26:27 |
| Message-ID: | 20061215212627.GU14237@alvh.no-ip.org |
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| Lists: | pgsql-hackers |
Andrew Dunstan wrote:
> I don't understand how we decide that everybody who needs a given
> event+message has got it, if we don't know who (if anyone) is listening?
> How do we decide that we no longer need the info in the shmem buffer?
Keep a pointer in shared memory for each listener backend, saying how
far it has scanned the ring? There would be a single writing pointer,
so it's trivial to see when the ring is "full".
> Timeout? sinval issues a reset if the buffer becomes full, but we can't
> do that here.
Just have NOTIFY block when the buffer is full, and maybe issue a
warning so that the user knows that he should increase the ring size.
> Are we keeping use of SIGUSR2 in this scheme?
What for? Just protect the write pointer with a lwlock and have
listeners check whether somebody has written something.
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