Introducing Support for Move Operations in Melda CRDT

Abstract

In this paper, we present an extension to Melda (a library which implements a general purpose delta state JSON CRDT) to support move operations. This enhancement relies on minimal changes to the underlying logic of the data structure, has virtually no runtime overhead and zero storage overhead compared to the original version of the library, ensuring simplicity while addressing multiple use cases. Although concurrent reordering of the elements in a list was already supported in the original version of the library, moving objects between different containers lead to undesired outcomes, namely duplicate entries. To address this problem we revisited the original approach and introduced the necessary changes to support for relocating elements within a JSON structure. We detail those changes and provide some examples.