Re: jsonlog logging only some messages?

On Mon, Feb 26, 2018 at 05:38:56PM +0000, Greg Stark wrote:
> I tried loading the jsonlog module from
> https://github.com/michaelpq/pg_plugins into Postgres 9.6.
>
> However it seems it resulted in logs only for session log messages but
> not any background worker log messages. We have log_checkpoints set
> but there were no log messages in the json log about checkpoints. Nor
> were there any from autovacuum.

Hm. I have just loaded jsonlog on a 9.6 and 10 instance where
log_checkpoints is enabled with this background worker which logs a
simple string every 10s:
https://github.com/michaelpq/pg_plugins/tree/master/hello_world

Both checkpoint logs and the logs of the bgworker are showing up for me.

> Also I have log_destination set to stderr,cvslog and as I understand
> it the jsonlog module effectively overrides the "stderr" output which
> goes to the file named *.log (which I find super confusing,
> incidentally). But I was expecting to get the csv file as well. We
> didn't, we only got the *.log file with the (partial) json logs. Is
> there something I'm missing here or is this unexpected?

Yeah, that's unfortunately expected... jsonlog enforces
edata->output_to_server to false, which has the advantage of disabling
extra log outputs, but also has the advantage of preventing duplicate
entries into stderr. One way that I can see to solve things would be to
patch the backend and get output_to_server replaced by a filter which
allows a plugin to choose what are the extra output types allowed. In
this case you don't want stderr later on, but would still want csvlog to
happen, instead of having an all-or-nothing switch. I haven't tested,
but it could be possible to have as well jsonlog enforce Log_destination
to only use csvlog after it generates its entry so as stderr is not
duplicated by csvlog gets though. Not sure how you would reset the
parameter though, so you may perhaps want to invoke an extra plugin
which outputs to csvlog as jsonlog cascades through things.
--
Michael