US Patent 7953710 Multi-master database synchronization without loss of convergence

Tombstones can be removed from a data store without data corruption. Tombstones placed into a forgotten knowledge list can be compared against each other and/or items in a tombstone table, and deleted when tombstones representing subsequently deleted items are extant. Also, creation database version information can be kept along with database items, and databases can record database version information when they synchronize. If a synchronizing database discovers an item that it does not have, but the creation database version information associated with the item reflects that the synchronizing database “should” have the item, then it can be inferred that the item was subsequently deleted, and item resurrection can be prevented.