title: List variables set by set_config, in postgres
body: <p>We've converted a ton of Oracle PL/SQL packages into PostgreSQL PL/pgSQL. We didn't know much about Postgres at the time, so relied on internet's help a lot. Because PL/pgSQL lacks a "better way" of implementing session-level variables, we ended up translating PL/SQL package global variables as PostgreSQL configuration variables using <code>set_config()</code> function, more than we should've. They are now scattered all over the code.</p>
  
  <p>Is there a way to query all variables and variables set by <code>set_config()</code> function?</p>
  
  <p>Judging by their behavior in transaction, my assumption is that they are stored in some system-generated (possibly temp) table. If so, I'd like to know its name, and whether it's possible to query it.</p>