Pass additional data in connection for use by PGSQL Trigger I would like to add some auditing triggers to PG, to log all changes to tables.  I have found an example trigger ( wiki.postgresql.com - 9.1+ audit trigger ), which gets me started. 

What I would like to do is pass along some additional data automatically, such as the user-id or other key, so that the trigger can link the change back to the application user that made it. The basic flow would go like this:


Get a connection for the current request
Run custom SQL to set a context variable (set conn_context = {userid};)
Read / parse that variable inside the trigger
Write the value to a log table along with the other information


When using MS SQL I was able to execute a statement that set the context for the connection by executing SET CONTEXT_INFO ...data....  I am hoping there is a way to do this for PG; I haven't found one yet, but that may just be bad google-fu.
Old question, but still valid, so here is what I ended up using.
On 9.6 and above, to set the values either of the following will work:

select set_config('app.userid', '3', true)
SET LOCAL &quot;app.userid&quot; = 3; (or '3')

To read the value out,

select current_value('app.userid')

I ended up wrapping the lookup for the userid or other field in a function, to handle the type conversion(s) and the fact that it might not be set:
CREATE OR REPLACE FUNCTION app_get_userid() RETURNS INT AS $$
DECLARE userid integer;
BEGIN
    BEGIN
        userid := current_setting('app.userid');
    EXCEPTION
        WHEN OTHERS THEN userid := NULL;
    END;
    return userid;
END;
$$ LANGUAGE plpgsql;