Re: Listen / Notify - what to do when the queue is full

On Sun, 2010-02-14 at 17:22 +0100, Joachim Wieland wrote:

> New patch attached, thanks for the review.

Next set of questions

* Will this work during Hot Standby now? The barrier was that it wrote
to a table and so we could not allow that. ISTM this new version can and
should work with Hot Standby. Can you test that and if so, remove the
explicit barrier code and change tests and docs to enable it?

* We also discussed the idea of having a NOTIFY command that would work
from Primary to Standby. All this would need is some code to WAL log the
NOTIFY if not in Hot Standby and for some recovery code to send the
NOTIFY to any listeners on the standby. I would suggest that would be an
option on NOTIFY to WAL log the notification:
e.g. NOTIFY me 'with_payload' FOR STANDBY ALSO;

* Don't really like pg_listening() as a name. Perhaps pg_listening_to()
or pg_listening_on() or pg_listening_for() or pg_listening_channels() or
pg_listen_channels()

* I think it's confusing that pg_notify is both a data structure and a
function. Suggest changing one of those to avoid issues in
understanding. "Use pg_notify" might be confused by a DBA.

-- Simon Riggs           www.2ndQuadrant.com