To: Florian Weimer <fweimer@bfk.de>
cc: pgsql-sql@postgresql.org
Subject: Re: Transaction-specific global variable 
In-reply-to: <82zkqdscuc.fsf@mid.bfk.de> 
References: <82zkqdscuc.fsf@mid.bfk.de>
Comments: In-reply-to Florian Weimer <fweimer@bfk.de>
	message dated "Thu, 03 Feb 2011 09:10:19 +0000"
Date: Thu, 03 Feb 2011 11:31:46 -0500
Message-ID: <23728.1296750706@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>

Florian Weimer <fweimer@bfk.de> writes:
> hstore greatly simplifies creating triggers for logging table changes,
> which is great.  However, when creating a log record, I would like to
> include information about the party who made this change.  We
> generally do not allow direct database access for application code, so
> the PostgreSQL user does not provide sufficient information on its
> own.  Instead, I'd like to create a transaction-specific variable
> which stores context information to be included in the log table.  I
> suppose I could create a stored procedures in C which provides this
> functionality, but I wonder if there is already something similar I
> could reuse.  For instance, I could reuse the application_name
> configuration variable, but this seems a bit gross.

You could abuse the custom-GUC-variable mechanism: just set
custom_variable_classes and then define some variable that doesn't
actually have any underlying loadable module.

			regards, tom lane