Re: A simple extension immitating pg_notify - Mailing list pgsql-general
I understand that:
1) you like to use postgres as a "bus" to transfer messages between connected clients;
2) only one database server is concerned (no redundancy at all);1) you like to use postgres as a "bus" to transfer messages between connected clients;
3) it is the client code (perl, php ...) that send the notification (ie, notifications are not sent by triggers for example)
May be you could dedicate one of your database to do this; all clients could listen messages on this database and some client code would decode the payload and does its job.
Sylvain
2016-07-24 15:55 GMT+02:00 Melvin Davidson <melvin6925@gmail.com>:
On Sun, Jul 24, 2016 at 9:35 AM, Adrian Klaver <adrian.klaver@aklaver.com> wrote:On 07/24/2016 03:31 AM, Mehran Ziadloo wrote:I'm sorry, you are right. Let me rephrase that.
What I meant was that the notifications are received by the client
connections
as if it was generated within their corresponding database (let's name the
database with a client connection listening to it; DB_C), then a
notification
generated by a NOTIFY command within DB_X like this:
pg_notify_db('DB_C', some_channel, 'payload');
can be heard by the client. Of course, the client needs to know which
database
has sent the notification but I think we can skip that part since we can
easily
include database name in the notification's payload if necessary.
That was one of the two solutions. The other one is like this:
pg_notify_all(some_channel, 'payload');
And this one sends the notification to all of the client connections,
regardless of which database they are connected/listening to.
I hope it makes sense now.
As to how to start writing an extension:
https://www.postgresql.org/docs/9.5/static/extend-extensions.html
As to how NOTIFY/LISTEN works:
https://git.postgresql.org/gitweb/?p=postgresql.git;a=blob;f=src/backend/commands/async.c;h=beef574076c257db0a868b39a946565185f6c53e;hb=ba37ac217791dfdf2b327c4b75e7083b6b03a2f5
--
Adrian Klaver
adrian.klaver@aklaver.com
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http://www.postgresql.org/mailpref/pgsql-generalI am not so sure another extension is needed. Would it not make more sense just to use the dblink extension?
https://www.postgresql.org/docs/9.5/static/contrib-dblink-function.htmlJust make a table that contains the names of the other databases and connection info.Then the same trigger that calls the function for NOTIFY or pg_notify(text, text) could just aseasily call a function with dblink that determines which database needs the notify and raises it there.
--Melvin Davidson
I reserve the right to fantasize. Whether or not you
wish to share my fantasy is entirely up to you.
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