Django没有重用与CONN_MAX_AGE = 60的MySQL连接

Question

I am using Django 1.9.2 in development ( DEBUG=True ) with MySQL 5.6.23. Below is my database settings

DATABASES = {
    'default': {
        'ENGINE': 'django.db.backends.mysql',
        'NAME': 'dbname',
        'USER': "django",
        'PASSWORD': 'password',
        'HOST': 'localhost',
        'PORT': '3306',
        'CONN_MAX_AGE': 60,
    }
}

I am querying MySQL to get the number of active connections with the command below:

show status where `variable_name` = 'Threads_connected';

It yield result like this

+-------------------+-------+
| Variable_name     | Value |
+-------------------+-------+
| Threads_connected | 10    |
+-------------------+-------+
1 row in set (0,00 sec)

Every time I make a new request to Django, the number of connected threads increase until I get (1040, 'Too many connections') when the number Threads_connected=151 . Furthermore, connections are not closed after 60s.

This behavior does not seem to happen in production ( DEBUG=False ).

Answer 1

You are running Django in development mode, so the CONN_MAX_AGE is not effective because each request is served by a different thread. From the docs :

The development server creates a new thread for each request it handles, negating the effect of persistent connections. Don't enable them during development

About the connection not being closed after 60 seconds: timed out connections are closed on the next request, so just make a new request to django after more than 60 seconds, it should detect the obsolete connection and close it.