Hi all, I'm trying to build chat functionality into my Google App Engine web application. The basic idea is that User loads a chat page that employs AJAX calls to poll new chat messages in the channels he/she is following every few seconds, and user can also write to the channels using AJAX.
1. A simple channel entity with a list property containing message strings is OK for channels with a few users and infrequent updates, but once a channel becomes "hot" (likely to happen for the purpose I have in mind), there's suddenly 300 users polling a single channel entity every few seconds, and new lines being added every few seconds. Once the entity contains something like 1000 message strings, this starts to sound a bad idea. 2. Creating a new entity type for message line with timestamp is also possible, but polls would then be of type "give me all messages since timestamp X", and every poll would need a filtered query into message pool, and with a thousand users this would mean something in the ballpark of 200 queries per second. Also, this solution doesn't play well with memcache. Changing timestamp to incremental counter would improve the situation, but I still don't know if it's efficient to cache each chat message as a single object in memcache? 3. The solution I'm now considering would be to "page" a chat channel, so one chat page entity would contain something like 50 messages at most (as a list type property), and when that limit is reached, a new page is created. Each channel object would have a reference to the current page and previous page, so new users joining the channel would have quick access to >50 of the latest messages. Pages would also lend themselves well for memcaching. A poll would then be of type "If have the messages until page 3, message 23 - what's new?". Any ideas or comments on the different options? Am I worrying too much about this? I know this currently is not issue, but my aim is that the data structure should gracefully and efficiently handle something like 2500 simultaneous users, each polling typically one to ten different channels and contributing to one or two. -- You received this message because you are subscribed to the Google Groups "Google App Engine" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/google-appengine?hl=en.
