Is Tornado really non-blocking?

Question

Tornado advertises itself as \"a relatively simple, non-blocking web server framework\" and was designed to solve the C10k problem. However, looking at thei

Answer 1

Yes; this is not a fully non-blocking web server at all.

A non-blocking webserver doesn't block, using non-blocking APIs for file I/O, database access, and so on, to ensure that one request that has to wait for something to finish doesn't prevent other requests from being processed. This applies to everything that might block the server, including database access.

There's nothing as silly as "causality violation" in having non-blocking database access; it makes perfect sense to run a non-blocking query related to one request, and to process other requests while that's still running. In practice, this will usually mean making multiple connections to the database backend.

Note that if you're trying to run ten thousand concurrent requests, be careful: most database backends can't cope with this. If you have more than a few dozen database requests to run in parallel, you probably want something like a connection pooler, to allow the web server to make lots of database connections without swamping the backend. This will cause requests to block, waiting in a queue to get database access, but doing it this way means it's not blocking the whole server--just the requests that need the database.