For some version-control systems, making Bulidbot aware of new changes can be a challenge. If the pre-supplied classes in see Change Sources are not sufficient, then you will need to write your own.
There are three approaches, one of which is not even a change source. The first option is to write a change source that exposes some service to which the version control system can "push" changes. This can be more complicated, since it requires implementing a new service, but delivers changes to Buildbot immediately on commit.
The second option is often preferable to the first: implement a notification service in an external process (perhaps one that is started directly by the version control system, or by an email server) and delivers changes to Buildbot via see PBChangeSource. This section does not describe this particular approach, since it requires no customization within the buildmaster process.
The third option is to write a change source which polls for changes - repeatedly connecting to an external service to check for new changes. This works well in many cases, but can produce a high load on the version control system if polling is too frequent, and can take too long to notice changes if the polling is not frequent enough.