Thread: Please clarify docs on user-defined settings for SET and RESET

The following documentation comment has been logged on the website:

Page: https://www.postgresql.org/docs/17/sql-set.html
Description:

Hello,

I'm reading through and playing with the SET and RESET docs and I'm somewhat
unclear about the behavior of arbitrary user settings that *don't* have a
session default.

For example a user defined setting is not available:

> psql -h localhost -U postgres
psql (14.17)
Type "help" for help.

postgres=# select current_setting('foo.bar');
ERROR:  unrecognized configuration parameter "foo.bar"
postgres=# select current_setting('foo.bar', true);
 current_setting 
-----------------
 
(1 row)

postgres=# select current_setting('foo.bar', true) is null;
 ?column? 
----------
 t
(1 row)

And then I set it:

postgres=# set foo.bar = 'foo!bar';
SET
postgres=# select current_setting('foo.bar');
 current_setting 
-----------------
 foo!bar
(1 row)

And then I reset it to… what?

postgres=# reset foo.bar;
RESET
postgres=# select current_setting('foo.bar');
 current_setting 
-----------------
 
(1 row)

postgres=# select current_setting('foo.bar') = '';
 ?column? 
----------
 t
(1 row)

It seems that the assumed/implied default value for settings that did not
exist for a session is the empty string? It would be useful to document that
behavior explicitly.

We can take this further:

> psql -h localhost -U postgres
psql (14.17)
Type "help" for help.

postgres=# select current_setting('foo.bar', true) is null;
 ?column? 
----------
 t
(1 row)

postgres=# select current_setting('foo.bar', true) = '';
 ?column? 
----------
 
(1 row)

postgres=# reset foo.bar;  -- Same as: SET foo.bar TO DEFAULT
RESET
postgres=# select current_setting('foo.bar', true) is null;
 ?column? 
----------
 f
(1 row)

postgres=# select current_setting('foo.bar', true) = '';
 ?column? 
----------
 t
(1 row)

Note how the value & type of the user setting changes, somewhat unexpectedly
(to me).

Furthermore, it seems impossible to actually *remove* such a user defined
settings completely, correct? That too, I miss stated explicitly in the
documentation.

Much thanks!
Jens

It seems that the assumed/implied default value for settings that did not
exist for a session is the empty string? It would be useful to document that
behavior explicitly.

Furthermore, it seems impossible to actually *remove* such a user defined
settings completely, correct? That too, I miss stated explicitly in the
documentation.