Re: Where to store some session based info? - Mailing list pgsql-general

On 3/25/26 10:20 AM, Durumdara wrote:
> Hello!
>
> Sometimes we have to use "Current User ID", and "User Name" in the
> Triggers to make a log into a table. These values are based on our User,
> not in the PSQL role.
>
> Now we use a temporary table to do this.
> When the user logged into the application, we created a temporary table
> with the same name (user_info) and structure. This holds the data (id,
> name, machine info, ip address).
>
> In the trigger we try to find this table (in the LOCAL_TEMPORARY schema).
> Then we read the row into a JSON record, and then into PLPGSQL variables.
> Tables can exist with the same name, so this is the safest solution.
> If the User  ID is invalid (none or empty) that means this is a
> background operation, and then we don't need to log the changes.
>
> But maybe there is a better way to somehow store some session based data
> and use it in the triggers.
> Because if these selects are slow, the trigger is also slow. So when I
> start an UPDATE command in a big table, maybe this slows down the whole
> operation.
>
> Note:
> A table with the PID key is not enough, because the PID is a repeated
> value.
> I logged it and in the Windows system there are many of the same values
> (10001, 10004, etc.).
> Ok, I can combine with session creation time. But for this I also need
> to start a select in the pg_stat_activty table.
>
> So maybe you have an easier way to point to a record in a session.
> Important: the PG servers are different, the lesser version is 11, and
> we have only a Database Owner role. We can't configure the server.
>
> What is your opinion? Is there any way to get session based data?
> As I read before, we can't set the session variables onfly.

Maybe SET?:

https://www.postgresql.org/docs/current/sql-set.html

With LOCAL it is scoped to a transaction.

Otherwise it persists for session unless a transaction is rolled back.

As example:

CREATE OR REPLACE FUNCTION public.session_test()
  RETURNS void
  LANGUAGE plpgsql
AS $function$
DECLARE
     _test_var varchar := current_setting('test.session_var', 't');
BEGIN
     RAISE NOTICE 'Variable is %', _test_var;
END;
$function$


No variable set:

test=# select session_test();
NOTICE:  Variable is <NULL>
  session_test
--------------

(1 row)

Variable set:

test=# begin ;
BEGIN
test=*# set local test.session_var = 'test';
SET
test=*# select session_test();
NOTICE:  Variable is test
  session_test
--------------

(1 row)

>
> Best regards
> dd
>
>


--
Adrian Klaver
adrian.klaver@aklaver.com