canceled is set to true if the response is for a cancel watch request or if the start_revision has already been compacted. No further events will be sent to the canceled watcher.
compact_revision is set to the minimum index if a watcher tries to watch at a compacted index.
This happens when creating a watcher at a compacted revision or the watcher cannot catch up with the progress of the key-value store.
The client should treat the watcher as canceled and should not try to create any watcher with the same start_revision again.
created is set to true if the response is for a create watch request. The client should record the watch_id and expect to receive events for the created watcher from the same stream. All events sent to the created watcher will attach with the same watch_id.
framgment is true if large watch response was split over multiple responses.
watch_id is the ID of the watcher that corresponds to the response.
cancel_reason indicates the reason for canceling the watcher.