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@xxxxxxxxxxxxx>
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
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
