Re: [HACKERS] WIP: Separate log file for extension

Masahiko Sawada <sawada.mshk@gmail.com> wrote:

> On Fri, Aug 25, 2017 at 4:12 PM, Antonin Houska <ah@cybertec.at> wrote:
> > Attached is a draft patch to allow extension to write log messages to a
> > separate file.
>
> Does it allow postgres core code to write log messages to multiple log
> files as well? I can imagine a use case where we want to write log
> messages to separate log files by error level or purpose (server log
> and SQL log etc).

At low level it should work as long as several log streams are reserved for
the core code. However, as every single stream needs multiple variables, I
have no idea how to configure those additional streams w/o adding many new GUC
variables to the core.

Also the discussion what should (not) be logged separate would probably be
difficult.

Specifically to log SQL statements to a separate file, I think (but not
verified) that you can write an extension that reserves a stream for itself
and also uses emit_log_hook to recognize SQL statements among the logged
messages. If the hook adjusts the syslogger_stream field of ErrorData
accordingly, the message should end up in the separate file.

--
Antonin Houska
Cybertec Schönig & Schönig GmbH
Gröhrmühlgasse 26
A-2700 Wiener Neustadt
Web: http://www.postgresql-support.de, http://www.cybertec.at