How Rails handles database connection in the background?

I am trying show controller specific pages in my rails app when the database connection goes away. I do this by catching the Mysql::Error in the rescue_action method and rendering appropriate pages. When the mysql service alone is stopped , i get the Mysql::Error exception really quickly and i could render the pages without any delay.

But when the server itself is shut down, rails takes 3 mins to throw the Mysql::Error and after 5-6 request the whole website becomes unresponsive.

I tried to figure out, which method in rails framework takes such a long time , when the mysql server is shut down. It was a method connection.real_connect (in the active record mysql_adapter file),which took 3 mins to return with an exception.

so i decided to timeout out this method using systemTimer gem. This monkey patch worked perfectly, when i start the website with database connection and immediately shutdown the database server.

But when i start the website with database, and access the website for sometime and then shut down the database server, it doest work at all. and the whole website becomes unresponsive as before. I wonder what is the difference between the two scenarios.

I think i need to know more in detail about how rails handle database connection . how it reacts when the database connection goes off. so that i could identify exact places where i can put monkey patches and make it work for my spefic requirement. I havent seen any relevant article explaining this.

Any help will be very useful for me



I've not tried this, but you can add connect_timeout as one of the specified options (along with port, host, etc) for the MySQL connection in the database.yml file. That value is passed to the real_connect call to establish the connection to MySQL.

Furthermore, since you are experiencing a delay after the initial connection is made and the DB is shutdown, you may need to use the read_timeout config option.

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