Re: WIP: Separate log file for extension

From: Antonin Houska <ah(at)cybertec(dot)at>
To: Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com>
Cc: PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: WIP: Separate log file for extension
Date: 2017-08-30 12:08:34
Message-ID: 10280.1504094914@localhost
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Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:

> On Fri, Aug 25, 2017 at 4:12 PM, Antonin Houska <ah(at)cybertec(dot)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

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

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