Activity feed on NO-SQL storage

HI...i have been thinking about a notifications system...which send users an alert when data has arrived for some subscription their made or a friend has made some activity (facebook style).

The thing is i would like to storage it using a no-sql database (mongodb, cassandra) bu开发者_JAVA技巧t i cant still figure out how to know when data has changed...should i handle that myself? or the no-sql databse?...like registering a callback??...or just making a query every n seconds?

Thanks in advance!

MongoDB has a tailable cursor that you might find useful for this use case.

You also may want to check out Redis pubsub queues. http://redis.io/topics/pubsub