I tend to 'clean' mine out every once in a while. Load it up, cmd(ctrl on windows)+a to select it all and copy/paste it into something simple (i use TextEdit on my mac, windows equivalent would be Notepad i suppose?) using rich text to ensure the formatting etc is retained. A four month log came out at about 2mb which i then shared via a dropbox style upload for players to access before clearing out the chat archive on the campaign settings page. Not quite as elegant as keeping it all in-house i grant you, but effective none-the-less.