jetpack_sync_prevent_sending_post_dataFilters whether to prevent sending post data to .com Passing true to the filter will prevent the post data from being sent to the WordPress.com. Instead we pass data that will still enable us to do a checksum against the Jetpacks data but will prevent us from displaying the data on in the API as well as other services.
jetpack_sync_processed_actionsAllows us to keep track of all the actions that have been sent. Allows us to calculate the progress of specific actions.
jetpack_sync_send_dataFires when data is ready to send to the server.Return false or WP_Error to abort the sync (e.g. if there’s an error) The items will be automatically re-sent later
jetpack_sync_before_send_{$item[0]}Modify the data within an action before it is serialized and sent to the server For example, during full sync this expands Post ID’s into full Post objects, so that we don’t have to serialize the whole object into the queue.
jetpack_sync_constantTells the client to sync a constant to the server
jetpack_full_sync_constantsTells the client to sync all constants to the server
jetpack_sync_remote_actionFires when an action is received from a remote Jetpack site
jetpack_sync_remote_actionsFires when an array of actions are received from a remote Jetpack site
jetpack_sync_multi_request_failFires when the server receives two concurrent requests from the same blog
Jetpack Developer Resources 