What's a good Flask/Python/WSGI analog to the PHP Apache shared memory stores like apc_store/apc_fetch?

Question

I've done a couple of years of large-scale game server development in PHP. A load balancer delegates incoming requests to one server in a cluster. In the name of better performance, we began caching all static data (essentially the game world's model objects) on each of the instances in that cluster, directly in Apache shared memory, using apc_store and apc_fetch.

For a number of reasons, we're now beginning to develop a similar game framework in Python, using the Flask microframework. At first glance, this instance's memory store is the one piece that doesn't appear to translate directly to Python/Flask. We're presently considering running Memcached locally on each instance (to avoid streaming fairly large model objects over-the-wire from our main Memcached cluster.)

What can we use instead?

Answer 1

I would think that even in this case you might want to consider having a centralized key/value store system rather than a series of independent ones on each server. Unless your load balancer always redirects the same users to the same servers you could run into a case where a user's requests are routed to different servers each time so each node would have to retrieve the game state instead of accessing it from a shared cache.

Also the memory strain that a local key/value store on each system might incur could slow down your game server's other functions. Though that largely depends on the amount of data being cached.

In general the best approach would be to run some benchmarks to see what kind of performance you'd get with a memcached cluster and the types of objects you're storing vs local storage.

Depending on what other features you want from you key/value store you might also want to look into some alternatives like mongodb (http://www.mongodb.org/).

Answer 2

[Five-months later]

Our game framework is done.

In the end, we decided to store the static data in fully initialized sqlalchemy model instances in each web server. When a newly-booted game server is warming up, these instances are first constructed by hitting a shared MySQL db.

Since our Model factories defer to an instance pool, the Model instances need only be constructed once per deployment per server – this is important, because at our scale, MySQL would weep under any sort of ongoing load. We accomplished our goal of not streaming this data over the wire by keeping the item definitions as close to our app code as possible: in the app code itself.

I now realize that my original question was naive, because unlike in the LAMP stack, the Flask server keeps running between requests, the server's memory itself is "shared memory" – there's no need for something like APC to make it so. In fact, anything outside of the request processing scope it self and Flask's threadsafe local store, can be considered "shared memory".