CometD is a scalable HTTP-based event routing bus that uses an AJAX push technology pattern known as Comet. It implements the Bayeux protocol. Long polling, also called Comet programming, allows emulation of an information push from a server to a client.

What is CometD client?

CometD ships a JavaScript client library, a Java client library and a Java server library. This allows you to write applications in the browser with fine-grained logic and control on the server.

What is Salesforce streaming API perform long polling?

The Salesforce implementation uses long polling connections to the server that will be able to notify the client on changes. This differs from traditional polling in that it keeps an incoming request open until an event is fired and then sends the response.