How detailed do you want to get?

If you're using Python or C or something else to use redis as a server, it's probably just as fast as Q/KDB, and some informal benchmarking supports this:

    redis-server &
    redis-benchmark -t set -n 1000000 -c 1 -P 1000000
    0.00% <= 1368 milliseconds

v.

    q)h:neg hopen`:localhost:1234
    q)\t 1000000 h/"a:69"
    1013

However I don't think this necessarily a good way to build your system, because if you're going to do a million of (read something write) every second, and then do a million of (read store), then you might as well write it in KDB and just make it (read something store) and save yourself 40% on your heating bill.

It seems KDB excels at queries, joins, and aggregates on large datasets. I have limited experience with redis, but if that type of code would need to be written in c/python with redis then KDB may have a performance and productivity lift. I would like to see an example like that.

Another benchmark is here: http://kparc.com/q4/readme.txt

Like what?

A program in KDB instead of a program in Python and Redis?

Here's an implementation of a multiuser group chat in KDB:

https://github.com/srpeck/kchat/

and here's one in Python and Redis:

http://programeveryday.com/post/create-a-simple-chat-room-wi...