Re: NOTIFY/LISTEN in Postgresql

Thx for the feedback I will take a look.

Here some details. Basically what I'd like to achieve:

Internet <-> AppliA <-> PostgreSQL <-> AppliB

1) AppliA receives a request from the internet and calls a Pg/SQL function.
2) The Pg/SQL function informs AppliB that there is some work waiting
(NOTIFY).
3) AppliB does the work and posts the result back to PostgreSQL.

... and now here's the problem -> The initial Pg/SQL function should give
back the result computed by AppliB -> It has to wait somehow and get
informed when the work from AppliB is done.

Thx & cheers,
Peter

2012/10/15 Craig Ringer <ringerc(at)ringerc(dot)id(dot)au>

> On 10/15/2012 08:54 PM, P. Broennimann wrote:
>
>> Hi there
>>
>> 1) Can a Pg/SQL function "listen" for a notification sent from an
>> external instance?
>>
>
> No, it's the other way around. A client can `LISTEN` for a `NOTIFY` sent
> by another client, either directly or via a PL/PgSQL function.
>
> What you want is a NOTIFY callback or NOTIFY trigger, something that
> invokes a function without any client action when a NOTIFY comes in. No
> such feature exists.
>
> I would like my stored function to pause/wait and continue its execution
>> once an external event (NOTIFY event) occurs.
>>
>
> Use an advisory lock, they're ideal for that job:
>
> http://www.postgresql.org/**docs/current/static/explicit-**
> locking.html#ADVISORY-LOCKS<http://www.postgresql.org/docs/current/static/explicit-locking.html#ADVISORY-LOCKS>
>
> 2) In Pg/SQL I can implement a loop (until something happens) to
>> pause/wait. This costs CPU time -> Is there another solution?
>>
>
> Depends on what you're waiting for. Details?
>
> Again, an advisory lock may be a candidate.
>
> --
> Craig Ringer
>