Redis 2.4.X is getting slower

We are using pairwise-api in the setup describe in https://github.com/allourideas/pairwise-api/wiki/Installing. If traffic goes up, the system is getting slower and slower. Most probably, it's because of redis because restarting redis makes the system getting faster again.
Did you observe this behaviour too? Do you (@lukebaker) have any advice how to takle this issue?