Synchronization of subsets of data including support for varying set membership

Abstract

An efficient way and general mechanism is provided to represent and exchange knowledge and/or partial knowledge across nodes when synchronizing between any two nodes including custom or move filters where set membership can change over time at a device as data items come in and out of filter scope. A first node sends a second node its knowledge and/or partial knowledge, including objects and versions of those objects. The second node compares its knowledge and/or partial knowledge with the knowledge and/or partial knowledge of the first node, and then sends the first node any latest versions of objects of which the first node is unaware. In addition, the second node sends its knowledge and/or partial knowledge to the first node. The first node then performs a similar object-by-object version comparison to determine any conflicts due to independent evolution of objects and any changes that can be sent to the second node in order to bring the objects of the second node up to date with the knowledge and/or partial knowledge of the first node. Replicas can track filters to efficiently support synchronizing with filtered replicas. Filter forgotten knowledge is also used to represent how recently a replica can guarantee to know which items have been in the filter. Ghosts can be used to represent items that have been in the filter recently but have currently moved out. Filter forgotten knowledge concept allows both new filters to be tracked when they are introduced into the community, as well as periodically cleaning up of tombstones and ghosts.