Re: Discussion on a LISTEN-ALL syntax
| От | David G. Johnston |
|---|---|
| Тема | Re: Discussion on a LISTEN-ALL syntax |
| Дата | |
| Msg-id | CAKFQuwYvRZPK=qpbHTpLWWLQU5DRxv16Mm7yZUk3VAkECLnAwA@mail.gmail.com обсуждение исходный текст |
| Ответ на | Re: Discussion on a LISTEN-ALL syntax (Trey Boudreau <trey@treysoft.com>) |
| Список | pgsql-hackers |
On Fri, Dec 20, 2024 at 2:42 PM Trey Boudreau <trey@treysoft.com> wrote:
> On Dec 20, 2024, at 2:58 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Seems reasonable in the abstract, and given the UNLISTEN * precedent
> it's hard to quibble with that syntax choice. I think what actually
> needs discussing are the semantics, specifically how this'd interact
> with other LISTEN/UNLISTEN actions.
My first pass at the documentation looks like this:
<para>
The special wildcard <literal>*</literal> cancels all listener
registrations for the current session and replaces them with a
virtual registration that matches all channels. Further
<command>LISTEN</command> and <command>UNLISTEN <replaceable
class="parameter">channel</replaceable></command> commands will
be ignored until the session sees the <command>UNLISTEN *</command>
command.
</para>
I just sent my thoughts here as well. The choice to "cancel all listener registrations" seems unintuitive and unnecessary - so long as we either document or handle deduplication internally.
As I noted in my email, * is a permit-all policy in a "deny by default" system. Such a system is allowed to have other more targeted "allow" policies existing at the same time. If the permit-all policy gets removed then those individual allow policies immediately become useful again. If you want to remove those targeted allowed policies execute Unlisten * before executing Listen *.
I dislike the non-symmetric meaning of * in the command sequence above but it likely is better than inventing a whole new syntax.
David J.
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