Milan Babuškov Milan Babuškov - 2 months ago 15
Node.js Question

Using MemoryStore in production

Today I ran my Node.js application in "production" mode for the first time and got this warning:

Warning: connection.session() MemoryStore is not
designed for a production environment, as it will leak
memory, and obviously only work within a single process.


I only need to run a single process, but what should I use instead? I want my sessions to reside in RAM for fast access. I also want to be able to discard all the sessions by simply shutting down the Node app.

It seems an overkill to install Redis, MongoDB or another database just for this simple task. I also don't understand why is MemoryStore included in Node when it should not really be used?

Answer

Ok, after talking to Connect developers, I got more information. There are two things considered memory leaks here:

  1. problem with JSON parsing which is already fixed in recent versions
  2. the fact that there is no cleanup of expired sessions if the users never access them (i.e. the only cleanup is on-access)

The solution seems to be rather simple, at least this is what I plan to do: use setInterval to periodically clean up the expired sessions. MemoryStore provides all() to get the list, and we can use get() to force reading and thus expire them. Pseudo-code:

function sessionCleanup() {
    sessionStore.all(function(err, sessions) {
        for (var i = 0; i < sessions.length; i++) {
            sessionStore.get(sessions[i], function() {} );
        }
    });
}

Now just call sessionCleanup periodically via setInterval() and you have automatic garbage collection for expired sessions. No more memory leaks.