CONN_MAX_AGE and others not being picked up from settings file

[Karl Kuehn]

In trying to solve some performance issues I am observing (probably our code) I tried to use the CONN_MAX_AGE setting documented here:
​https://docs.djangoproject.com/en/2.0/ref/settings/#conn-max-age

I have a pgbouncer instance setup, so it was easy to observe connections going to the database, and I found that regardless of that setting the connections were being dropped at the end of every request, regardless of what value I set (even invalid ones have no effect).

Using git grep CONN_MAX_AGE | grep '\.py:' I found that this value is never being read from the settings file, and only defaulted in django/db/utils.py:ConnectionHandler.ensure_defaults(). This is true both on current (as of this writing) master and version 1.11.1 (what we are currently using). It may well go farther back than that, but I have not checked.

I also checked ATOMIC_REQUESTS, and AUTOCOMMIT and they show the same pattern. Other values there are more complicated, and I did not check.

[Karl Kuehn]

I have created a pull request with one way of fixing this: ​https://github.com/django/django/pull/9625

[Tim Graham]

As Simon said on the pull request, "These settings should be defined per-DATABASES entry and not as top level settings."