I am playing around with building a chat application using PHP and CodeIgniter.
For this, I am implementing a cache \'buffer\' with memcached to hold the most recent
Have you looked into HTML5 socket connections? With a socket server, you do not need to store anything. The server receives a message from one subscriber, and immediately sends it back out to the correct subscribers. I have not done this myself using HTML5, but I know the functionality now exists. I have done this before using Flash which also supports socket conenctions.