Web feed RSS and Atom: both inefficient?

Question

As far as I understand, both web-feeds RSS and Atom request, starting at the client side, content from the server, and they do that at periodic intervals of time. It doesn't matter whether there is new content or not, the client checks for updates.

Wouldn't it be more efficient the other way round? Let the server announce new updates. In this scenario, it would have to keep track of the clients, and when each got what update. It would also have to send a message to each one. But still, it looks more efficient if client-server were not communicating when there are no new news.

Is there a reason why web-feeds are the way they are?

Answer 1

This model is not inherent to feeds (RSS or Atom), but to HTTP itself, where a client queries a server to get data. This is at this point, the only way in a pure client -> server model to determine whether there is any new data available or updated.

Now, in the context of server querying other servers, PubsubHubbub solves that with webhooks. Basically, when polling any given resource, a server can also "subscribe" by providing a webhook which will be called upon a change or update in the feed. This way the subscriber does not have to poll the feed over and over again.