Re: [HACKERS] log_destination=file

On 31 August 2017 at 13:49, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Magnus Hagander <magnus@hagander.net> writes:
>> On Thu, Aug 31, 2017 at 2:34 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Yes, it's pretty important, because of assorted stuff not-under-our-
> control that doesn't know about ereport and will just print to stderr
> anyway.  Some examples: dynamic linker can't-resolve-symbol failure
> messages, glibc malloc corruption error messages, just about any external
> module in plperl or plpython.  I don't find this to be negotiable.

So what happens now with these messages? My understanding is that
they're missing from the CSV logs and are simply inserted into the
text logs without any log_line_prefix? The logging collector doesn't
recognize these messages and reformat them for the CSV logs does it?

I'm actually asking because I'm more concerned with JSON logs or
msgpack logs. Currently these are supported with an emit_log_hook but
they can't capture these non-ereport logs either.

Also the CSV and emit_log_hook based logs don't have any convenient
way to turn them on and off and control the location and filename of
the logs. It would be nice if we could have something like

log_destinations='stderr=text,syslog=json,postgresql-%Y-%m-%d_%H%M%S.csv=csv'

>> Are you actually asking for a benchmark of if logging gets slower?
>
> Yes.

Personally I don't think it's "performance" so much as operational
issues that are more concerning. For all we know there are people out
there who tried to use the logging collector and found it didn't work
well on some system -- perhaps it interacted with systemd or something
else on the system -- and they switched back to just using stderr. I
don't know how to flush these users out though if there are any. Just
making this change early in a release cycle is the best we can do.