FWIW we went through a very similar process to that documented here by Github (~3 months ago). It was entirely due to operational reasons and nothing to with shortcomings in Redis itself. MySQL was the master record for 99% of our data while Redis was the master record for the other 1% (as it happens it was also a kind of activity stream). Having the single 'master' reference for our data reduced complexity to a degree that it was worth running a less computationally-efficient setup. We also have nowhere near Github's volume so we did not have to do such significant re-architecting to make unification possible.
Now we still use Redis for reading the activity streams and as LRU cache for all sorts of data, but it is populated like all of our specialised slave-read systems (elasticsearch, etc) by replicating from the MySQL log.
Now we still use Redis for reading the activity streams and as LRU cache for all sorts of data, but it is populated like all of our specialised slave-read systems (elasticsearch, etc) by replicating from the MySQL log.
Hope that helps!