This is a very old question but the problem is still present in 12.0 so, here's a workaround. You just have to hit Odoo with a scheduled task in the background. If you're using Linux, you're in luck as this is fairly easy with crontab. Here's a rule:

* * * * * wget -O - http://addresss:port/web?db=database_name_here >/dev/null 2>&1

This will access the login screen for the given database every one minute, so this should wake Odoo up. Also, no error or message will be returned so it's safe. I'm not sure if this has to be done for each database or just one per server though.

Taken from: https://stackoverflow.com/questions/13259530/using-cron-jobs-to-visit-url

Hello, I found the solution for this, you need to set the db_name conf in your configuration file.

db_name = 'your_database'

After doing this the database init when you run the server process.

Hope this help!