Tom, I understand all you’ve said. I was hoping for a different answer. C’est la vie.
I think I could justify the effort to ‘script’ psql. I’m not so sure I can justify the effort to write a standalone program. At least I have an answer. Thanks! /s/jr Consultant Concerto GR Mobile: 612.208.6601 Concerto - a composition for orchestra and a soloist > On 28Aug, 2017, at 6:08 PM, Tom Lane <t...@sss.pgh.pa.us> wrote: > > "David G. Johnston" <david.g.johns...@gmail.com> writes: >> On Mon, Aug 28, 2017 at 1:28 PM, Jerry Regan < >> jerry.re...@concertoglobalresources.com> wrote: >>> My concern is how, after LISTENing in psql, I can tell it what to do when >>> the NOTItFY is received. > >> As far as I am aware you cannot. > > Yes, and psql is not designed to do anything of its own accord, > so I think the answer is really "use another program". > >> "Whenever a command is executed, psql also polls for asynchronous >> notification events generated by LISTEN and NOTIFY." > > Exactly. If you don't feed it a command, it just sits there. > >> I suspect the feature request would be something like: >> \set NOTIFY_PROGRAM './process-notify-request.bash' (or an equivalent >> meta-command) >> And psql would invoke said program and pass the content of the notification >> payload to it via stdin. > > Such a program could only execute after the next time you give a command > to psql. You could maybe imagine feeding it a continuous stream of dummy > commands, but that's pretty silly (and rather defeats the point of LISTEN, > which is to *not* eat cycles while waiting). > > This isn't something that could be easily fixed, AFAICS. Even if we > wanted to make psql pay attention to asynchronous data arrival, how > would we get control back from libreadline? And what would happen > if the user had typed a partial line of input? > > You really are much better off creating a program that opens its own > connection to the DB and sits there listening. psql cannot help you > meaningfully with this request, and I can't see a way to make it do > so that wouldn't be a monstrous kluge. > > regards, tom lane
