Tornado multiple processes: create multiple MySQL connections

Question

I'm running a Tornado HTTPS server across multiple processes using the first method described here http://www.tornadoweb.org/en/stable/guide/running.html (server.start(n))

The server is connected to a local MySQL instance and I would like to have a independent MySQL connection per Tornado process.

However, right now I only have one MySQL connection according to the output of SHOW PROCESSLIST. I guess this happens because I establish the connection before calling server.start(n) and IOLoop.current().start() right?

What I don't really understand is whether the processes created after calling server.start(n) share some data (for instance, global variables within the same module) or are totally independent.

Should I establish the connection after calling server.start(n) ? Or after calling IOLoop.current().start() ? If I do so, will I have one MySQL connection per Tornado process?

Thanks

Answer 1

Each child process gets a copy of the variables that existed in the parent process when start(n) was called. For things like connections, this will usually cause problems. When using multi-process mode, it's important to do as little as possible before starting the child processes, so don't create the mysql connections until after start(n) (but before IOLoop.start(); IOLoop.start() doesn't return until the server is stopped).