rlm_sql_null: No connections available and at max connection limit

[Alan DeKok]

On Jun 3, 2021, at 4:17 PM, Artis Caune <artis.caune at gmail.com> wrote:
> We use rlm_sql_null for accounting and auth logs which allow us to respond
> quickly and defer inserts from regional nodes when db or link is down.
> 
> Config is simple:
> 
> accounting {
>    ...
>    sql_accounting
> }
> 
> sql sql_accounting {
>        driver = "rlm_sql_null"
>        accounting {
>                logfile = "${sql_write_dir}/accounting.sql"
>                query = "INSERT INTO accounting ..."
>        }
> }
> 
> We get around 10-15 auth requests per sec and I don't see any errors for
> post-auth log.
> But we get around 180-200 acct requests per sec and I'm getting those
> errors for rlm_sql_null module:
> rlm_sql (sql_accounting): Cannot open new connection, already at max
> rlm_sql (sql_accounting): No connections available and at max connection
> limit

  Yeah, the main SQL module doesn't know that the "rlm_sql_null" driver doesn't connect to a real database.  It's the one downside of the abstractions we use.

> README.rst says we can leave the pool definition or delete it for _null
> module.
> 
> Wondering if there are some tweaks for the null module or it's a bug as
> there should be no max connection limit on this module ?

  Just configure a "pool" section, and set the maximum connection limit to a high value.  It will be fine.

> Also noticed that null module tries to connect to radius table but no
> db_name is configured:
> rlm_sql (sql_accounting): Driver rlm_sql_null (module rlm_sql_null) loaded
> and linked
> rlm_sql (sql_accounting): Attempting to connect to database "radius"
> 
> Why is it trying to connect to something if it should just append to
> logfile ?

  That's just an information message.  It doesn't mean anything for the rlm_sql_null driver.  It can be ignored.

  It's another side effect of the main SQL module not knowing that there's any difference between PostgreSQL, MySQL, Oracle, or NULL.

  Alan DeKok.