Redis: Performance comparison with SQL!!!

[sreeram.r...@outlook.com]

Hi All,

In our application, we're working to implement Redis as caching data-store and SQL for database.

1. Our application is domain-driven model.

2. Previously we were caching domain objects using app. server's In-memory (application servers was not distributed then).

3. Now we're implementing distributed architecture for our app. servers, so we're using Redis(1 master & 2 slaves) for centralized caching for all app. servers.

How we've implemented Redis,

1. I'm using StackExchange.Redis as our .Net client.

2. When a domain object has to be cached, I'm serializing(NetSerialization) entire domain object as RedisValue and caching the same.

Now when I do Load testing(50,000 iterations) for Redis comparing with SQL fetching the same domain object,

Avg. Time to retrieve from SQL   : 12.00949734 milliseconds

Avg. Time to retrieve from Redis : 9.418295734 milliseconds

Questions:

1. Difference of just 3 milliseconds between SQL & Redis, is it normal?! 

2. Is my requirement suitable Use case for Redis ?

[Marc Gravell]

There are a lot of variables here that make it very hard to generalise, for example:

- how big is the data (and keys)?
- is the time being dominated by serialization/deserialization? (if so, I can recommend a few other serializers :p)
- what does the test code look like? is it actually optimal?
- is the server load representative? (a single-threaded test loop over an otherwise silent database is good for repeatable numbers, but doesn't actually tell you much about real load)

Personally, assuming my servers are local to each-other, and the payloads aren't big: I'd expect lower numbers than that - based on my real world usage.

Do you have a test rig I can look at?

Marc

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[Marc Gravell]

Oh, and yes: that scenario is one of the things that is usually pretty expensive for SQL server and cheap for redis.

Finally, you haven't indicated your redis config - is it configured for persistence, for example? (Usually not required in a cache server)