I am trying to add cache to a Tornado application, with data in Mongo. I am using Redis as a shared cache store.
Since tornado is an asynchronous framework, I was thinking about using an async client for Redis, that uses tornado's ioloop to fetch data from Redis server. None of the existing solutions are very mature, and I heard the throughput of these clients are not good.
So my question is, if I use a synchronous Redis client like pyredis, will it negatively impact the performance of my app?
I mean, considering the Redis instance lives on the same LAN, the latency for a redis command is very small, does it matter whether it is blocking or not?
It's difficult to say for sure without benchmarking the two approaches side-by-side in your environment, but redis on a fast network may be fast enough that a synchronous driver wins under normal conditions (or maybe not. I'm not personally familiar with the performance of different redis drivers).
The biggest advantage of an asynchronous driver is that it may be able to handle outages of the redis server or the network more gracefully. While redis is having problems, it will be able to do other things that don't depend on redis. Of course, if your entire site depends on redis there may not be much else you can do in this case. This was FriendFeed's philosophy. When we originally wrote Tornado we used synchronous memcache and mysql drivers because those services were under our control and we could count on them being fast, but we used asynchronous HTTP clients for external APIs because they were less predictable.